THE EVOLUTION AND DISINTEGRATION OF MATTER. 

By FRANK WIGGLESWORTH CLARKE. 

INTRODUCTION. 

In any attempt to study the evolution of 

matter it is necessary to begin with its simplest 

known forms, the so-called chemical elements. 

During a great part of the nineteenth century 

many philosophical chemists held a vague 

belief that these elements were not distinct 

entities but manifestations of one primal substance-the protyle, as it is sometimes called. 

Other chemists, more conservative, looked 

askance at all such speculations and held fast to 

what they regarded as established facts. To 

them an element was something distinct from 

other kinds of matter, a substance which could 

neither be decomposed nor transmuted into 

anything else. This belief, however, was based 

entirely upon negative evidence-the inadequacy of our existing resources to produce such 

sweeping changes. Many important facts were 

ignored, and especially the fact that the elements are connected by very intimate relations, 

such as are best shown in the ·periodic law of 

Mendeleef, who, from gaps in his table of atomic 

weights, predicted the existence of three unknown metals, which have since been discovered. For these metals, scandium, gallium, 

and germanium, he foretold not only their 

atomic weights but also their most characteristic physical properties and the sort of compounds that each one would form. His 

prophecies have been verified in every essential 

particular. One obvious conclusion was soon 

drawn from Mendeleef's "law," although he 

was too cautious to admit it, namely, that the 

chemical elements must have had some community of origin. The philosophical speculations as to their nature were fully justified. 

. In 1873 I ventured to publish the suggestion 

that the evolution of planets from nebulae was 

accompanied by an evolution of the chemical 

elemen ts. 1 The validity of the nebular hypoth1Clarke, F. W., E volution and the spectroscope: P op. Sci. Monthly, 

January, 1873. 

esis was assumed, and the progressive chemical complexity of the heavenly bodies gave my 

argument its plausibility. The nebulae are 

chemically simple, the hotter stars more complex, the cooler stars and the Sun still more so, 

and the solid Earth the most complicated of all. 

The evidence for this statement was found in 

the spectroscopic researches of Huggins and 

Secchi, which seemed to me to be conclusive, 

although defective in one respect: instead of 

helium in the nebulae they reported nitrogen, 

for helium was yet to be discovered. This 

defect, however, did not invalidate my conclusions, which were promptly denounced as 

heretical but which have since been accepted as 

quite orthodox. Nearly a year later Lockyer 2 

put forth an analogous suggestion, based upon 

evidence of the same sort but starting from the 

other end. That is, he assumed that in the 

hotter stars the elements were dissociated, and 

his suggestion was received with a good deal of 

favor. As to the origin of the dissociated elements he had nothing to say. That the elements are really decomposable was the substance of his suggestion, which he followed up 

in detail in his later publications. 

With the discovery of radioactivity by Becquerel and of radium by Madame Curie a new 

era in chemistry began. It was at once found 

that at least some of the elements were really 

unstable; and the evolution of helium from 

·radium, discovered by Ramsay and Soddy, 

made the evidence complete. A derivation of 

one element from another had actually been 

observed. 

These discoveries opened a new field of 

research; and it was soon found that the 

elements at the top of the atomic-weight scale, 

namely, uranium and thorium, are spontaneously but slowly decaying, yielding more than 

thirty new substances which differ widely in 

2 Lockyer, J. N., Roy. Soc. Proc., vol. 21, p. 513; paper dated Nov. 20, 

1873. 

51 
· t 

52 SHORTER CON~IBUTIONS TO GENERAL GEOLOGY, 1923. 

stability. To each one a half-life period is 

assigned, some of them measured in thousands 

of years, others in fractions of a second. Amofig 

these substances are two new varieties of leadone derived from uranium, the other from 

thorium-which chemically are not distinguishable from ordinary or normal lead except by 

differences in their atomic weight and their 

specific gravity. The lead from thorium has 

an atomic weight about a unit higher and 

that from uranium about a unit lower than the 

atomic weight of normal lead. To this class 

of facts I shall recur later, as evidence in support of my arguments. That chemical elements 

can decay is the essential fact to be remembered. 

That the chemical elements were formed by 

a process of evolution from the simplest forms 

of matter can hardly be doubted now, but the 

process is not yet ended. They were developed 

at high temperatures; but when a certain stage 

was reached in the cooling mass they began to 

combine with one another to form the new 

class of substances which are known as comp.ounds. These substances obviously represent 

an advanced degree of complexity, with corresponding instability; and with varying conditions both combination and decomposition~ 

such as are reproducible by human agencies, 

constantly occur. By this extension of the 

evolutionary process the solid Ea;rth was built 

up, but in principle the proces~ is the same 

throughout. From the formation of the first 

elements to the chemical changes now taking 

place upon the Earth there is no real interruption. One line of progress has been followed 

until a maximum of natural complexity and 

instability is reached in the organic compounds 

that form the basis of all physical life, whether 

vegetable or animal. The same fundamental 

matter, governed by the same fundamental 

laws, appears from beginning to end of the 

evolutionary process. 

THE EVOLUTION OF THE CHEMICAL ELEMENT&. 

In any attempt to discuss the evolution of 

the chemical elements we have for guidance 

some facts and many analogies. That the 

most complex elements are unstable we have 

already seen, and it is suspected that all the 

others follow the same rule. Potassium and 

rubidium are feebly radioactive, a property 

which is an evidence of instability, and other 

confirmatory evidence will be cited later. 

Stability, however, is a relative term, and a 

substance that is stable under certain conditions becomes unstable under others. The 

prime factors that determine external stability 

are temperature, pressure, and chemical environment. For example, some compounds 

that are stable in anhydrous surroundings are 

decomposed in presence of water. Calcium 

carbonate, under ordinary conditions, is divided 

at high temperatures into carbon dioxide and 

lime, but he~ted in a' steel bomb it not only 

remains undecomposed but may even be 

melted, to form upon cooling a crystalline 

marble. Examp1es like this might be multiplied indefinitely. As a rule stability diminishes with increasing temperature but is 

favored by increased pressure. We may also 

assume that the more symmetrical an atom 

or compound is the more stable it is likely to be. 

Now, to return to our main problem, was 

the evolution of the elements a regular progression, such as might be represented by a 

smooth curve or a straight line; or was it 

irregular and quite independent of their order 

in the scale of atomic weights~ To answer 

this question we must try to imagine what 

happened in the development of the larger 

masses, the nebulae and the stars. On this 

subject there is a plausible hypothesis which 

has been favored by many astronomersnamely, that the nebula at first was relatively 

cool, that the temperature gradually rose to 

that of the hottest stars and then regularly 

declined to that of the end product of the series, 

the solid planet. A gaseous mass, contracting 

under the influence of gravitation, became 

warmer; at its center; where the pressure 

was greatest, the increasing condensation 

·generated still higher degrees of temperature, 

until a luminous nucleus was formed. As 

condensation went on with increasing intensities of pressure, the temperature continued 

to rise until the heat generated by compression 

was less than that lost by radiation into space, 

when cooling began. Although this hypothesis, in its crude form, is not universally a~­

cepted, it nevertheless gives a fair conception 

of that part of the evidence with which we 

are now concerned. The process of evolution 

from cool to hot and then to cool again is 

fairly outlined. The nucleus of the original 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 53 

nebula has its modern representative in the 

Sun. 

In all the foregoing discussion it has been 

tacitly assumed that the nebula from which 

the solar system was developed was similar in 

all essential respects to the planetary nebulae. 

The latter, as shown by their spectra, consist 

mainly of hydrogen, helium, and nebulium, 

with slight traces in some of them of carbon, 

nitrogen, and perhaps other elements. N ebulium is known only from its lines in the spectrum, and its atomic weight has been estimated 

by Fabry and Buisson as 2. 7, placing it between hydrogen and helium. In any further 

study of relations between the atomic weights 

of the elements, nebulium must be taken into 

account, and perhaps also coronium, so called 

from its lines in the spectrum of the 'solar 

corona. From its position in the corona it is 

assumed to be lighter than hydrogen and so 

would seem to be an even more primitive · element. That possibility can not be considered 

here; we must limit ourselves to the conditions actually seen in the nebulae. No assumption is made as to the possible ancestry of the 

nebular elements; they are the visible beginnings. 

Passing from the nebulae · to the stars and 

finally to the planets, the course of evolution 

has been one of uninterrupted gradations. 

There are no sharp lines of demarcation between one class and another. As for the elements their evolution has been admirably summarized by Campbell 3 in his lectures on the evolution of the stars. Without literal quotation 

and accepting the Harvard classification of the 

stars, I may briefly outline Campbell's summary 

as follows: After the gaseous nebulae there are 

first the blue stars of classes A and B. In 

class B, known as the helium stars, the hydrogen and helium lines are conspicuous, and in 

their later stages silicon, oxygen, and nitrogen 

are represented by a few absorption lines. In 

class A the hydrogen lines are the most prominent, and helium has nearly disappe11red. 

Lines of magnesium and calcium are also conspicuous, and those of iron and titanium are 

beginning to appear. 

In the spectra of stars of class F, the bluish-

. yellow stars, the metallic lines increase rapidly 

in prominence; .and in those of the yellow stars 

g Campbell, W. W., Pop. Sci. :Monthly, vol. 87, p. 209, 1915; Sci. 

Monthly, vol. I, pp. 1, 177, 238, 1915. 

of class G they appear in great number. Hydrogen is much less conspicuous. In the spec- · 

tra of the reddish-yellow stars of class K, which 

are weak in violet light, the metallic lines are 

more evident, and still more in those of the 

red stars of class M, in which the spectra also 

show absorption bands attributed to . titanium 

oxide. In the spectra of the very red stars of 

class N the violet end of the spectrum is almost entirely lacking, the metallic absorption 

is very strong, and bands representing carbon 

oxides are conspicuous. 

Such, in brief, was the probable course of 

elemental evolution in the passage from a gaseous nebula to the coolest and oldest stars. It 

is not necessary for my purpose to. go more · 

into detail on this phase of my subject. The 

literature relative to solar and stellar spectra 

is very extensive and is steadily increasing in 

volume. It involves many questions that I 

can not attempt to consider, even if I felt myself competent to do so. That the evolution 

of the elements has actually taken place seems 

to be established, and I must limit myself to · 

some of the chemical problems that are suggested by it. · 

Now, it is easy to see that in the process of 

evolution from nebula to Sun an orderly development of the elements could hardly have been 

possible. With changing pressure, changing 

temperature, and changing environment all . 

the conditions required for a regular progression according to the order of the atomic 

weights were lacking. In the hotter stars only 

the simplest and most stable elements were 

formed, and these in the greatest abundance. 

We have already seen that magnesium, calcium, 

titanium, and iron were among the earliest to 

appear, and that the others, between helium 

(atomic weight 4) and iron, either came later 

or were developed at first in much smaller 

quantities. As cooling went on more and more 

elements were generated, and in the Sun all 

the possible elements are presumably present, 

although only about half of them have been 

actually detected. It is conceivable that 

elements of different degrees of stability may 

have been formed simultaneously, one in that 

part of the cooling mass where the temperature 

and pressure were highest, another farther 

away from the center, under less rigorous conditions. This suggestion, however, is something which can not be proved. If the three 

•• A nunr-l\ 11 1\L' UINtf:. 
' 

54 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, lre3. 

nebular elements were the raw material from 

·which the other elements were built, their 

relative amounts must have been continually 

changing, so that as each new element appeared 

a new environment was established for all that 

followed. · At some time early in the course of 

evolution nebulium seems to have vanished, 

for its lines do not appear in the spectrum of 

any true star. Was it completely absorbed 

in building other elements~ The question is 

easy to ask but very, difficult to answer. 

That the cooling of a star made the formation 

of the less stable elements possible has already 

been assumed. But was the rate of cooling 

uniform, or was it subject to fluctuations~ 

To answe:~ this question we must bear in mind 

the clear distinction between. atoms and molecules, for here the elements as we know them 

differ widely. Some molecules, like those of 

zinc, cadmium, mercury, and the inert gases 

of the helium group, are monatomic. Hydrogen, nitrogen, oxygen, chlorine, bromine, and 

iodine are diatomic. Phosphorus and arsenic 

are tetratomic, and so on. For most of the 

elements we lack the positive information 

which we have for those just named. In ordinary chemical reactions the complex molecules are easily decomposed, and at high 

temperatures also decomposition is possible. 

The molecule of iodine, for example, is dissociated into its atoms at about 1, 700° C., a 

temperature much lower than that of even the 

coolest stars. In the· hotter stars all the 

elements present are probably in the atomic 

state, a considerable fall of temperature must 

take place before even diatomic molecules can 

be formed, and they may be regarded as a very 

primitive order of compounds. In the Sun 

and the cooler stars compounds in the ordinary 

sense of the term begin to appear and certain 

obvious consequences follow. 

Whenever two or more free atoms unite to 

form a chemical compound heat is given out;· 

and in most such unions, as in the formation of 

water from its elements, condensation has also 

its thermal value. I must here emphasize my 

use of the expression "free atoms," for they 

alone exist in the hotter stars. Such unions 

are rarely recognized in laboratory experiments, 

which deal not with direct combinations but 

nearly always with reactions. The heat of a 

reaction, which is usually called the heat of 

formation of a compound, is really the algebraic sum of three or more terms, some of 

which are positive and some negative. A reaction may be endothermic when the minus 

terms are in excess, as in the formation of 

hydriodic acid from its elements. Here the 

decomposition of the hydrogen and iodine 

molecules precedes the union of the momentarily free atoms. 

In the evolution of the elements we have, 

then, first the formation of individual atoms, 

and as cooling goes on their union into diatomic 

and polyatomic molecules becomes possible. 

Heat is given out, and the rate of cooling must 

be somewhat retarded. Whether the retardation is great or small it is impossible to say; 

but some increase of temperature, even if it is 

very slight, may fairly be assumed. In short, 

the rate at which a star cools is in all probability subject to fluctuations, which may influence the development of the more complex and 

less stable elements. When compounds, as we 

understand them, begin to be formed, the heating effect is likely to be relatively larger. The 

cooling of our Sun is almost certainly subject 

to this sort of retardation, and so its existence 

as a heat-giving luminary may be considerably 

prolonged. Heat of chemical origin, with its 

attendant condensations, must be taken into 

account in any serious attempt to discover the 

sources of solar energy. The formation of 

molecular from atomic hydrogen would alone 

give out a. vast amount of heat, about 82,000 

calories per gram-molecule. The supposed 

formation of helium from hydrogen need not be 

considered. The helium of the Sun is probably 

primordial. 

So far we have considered only the astronomical evidence relative to evolution, but that 

evidence is purely qualitative. For quantitative data we must study the so-called atomic 

weights and their relations, chemical and physical, with one another. The atomic weights, it 

must be remembered, are not absolute quantities, for no single atom has ever been directly 

weighed. They are really the expression of 

ratios, one element being assumed as a standard, with which the others can be compared, by 

methods that are so well known that it is not 

necessary to explain them here. These very 

elementary considerations are cited now because they are so familiar that they are often 

unconsciously ignored. If we think of the 

atomic weights as the combining numbers of 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 55 

the elements-that is, the proportions in which 

each one unites with others-it may be easier 

to a void confusion of ideas. 

At least three different standards of atomic 

weight have actually been in use. In the Berzelian system the atomic weight of oxygen was 

taken as 100, but that led to figures solarge for 

most of the elements that they were difficult to 

remember and inconvenient to use. The system was therefore abandoned, and the atomic 

weight of the lightest element, hydrogen, was 

assumed as unity, a much more natural and 

satisfactory plan than that of Berzelius. The 

hydrogen unit, H = 1, was in general acceptance 

until about 30 years ago, and it is still regarded 

favorably by many chemists. The only objection to it, at least until recently, was that very 

few of the atomic weights appeared as whole 

numbers, and the fractional parts were somewhat annoying. There was therefore a tendency among practical chemists to round the 

figures off to the nearest integers, for in many 

kinds of analytical work greater accuracy was 

not required. 

On the hydrogen scale the atomic weight 

of oxygen is 15.876, or nearly 16, a figure 

which is the basis of the system of atomic 

weights now generally used. With 0= 16 a 

considerable number of other atomic weights 

become close approximations to whole numbers and therefore more convenient to handle. 

That is the principal reason why the oxygen 

standard has been so commonly accepted by 

chemists. This reason would be more valid 

if determinations of atomic weight had been 

made by direct comparison with oxygen, 

whereas as a matter of fact comparatively 

few such determinations have been at all satisfactory. With some exceptions, by far the 

larger number of the best modern determinations have been indirect, with silver, chlorine, 

and bromine as intermediaries. This indirection, however, does not imply inaccuracy. The 

actual measurements are tbose of ratios. To 

discuss this subject in detail would take me 

too far from my main theme. 

We ·have already seen that hydrogen and 

helium are the two oldest elements of which we 

have any direct experimental knowledge. They 

also have the lowest atomic weight and are 

therefore the simplest. The astronomical and 

chemical lines of evidence are in complete har-

:mony. N ebulium may be left temporarily out 

of account. Hydrogen and helium, then, are 

the two elements with which to begin any 

detailed study of elemental evolution. The 

atomic weight of hydrogen, 1.0078, is the · 

starting point, with helium next in order. 

From these elements all other forms of matter 

may have been derived. There is much evidence in favor of this suggestion, although anything like absolute proof is lacking and perhaps 

unattainable. 

Of the mechanism of the processes by which 

the elements were built up we have no positive 

knowledge. It is, however, in the highest 

degree probable that they were formed under 

extremely high temperatures and pressures, such 

as we can not hope to reproduce experimentally. 

That the evolution of the elements was accompanied by a progressive condensation is evident; 

and it is also clear that the contraction from 

the primal highly attenuated nebula to the 

solid planet was something enormous-so great 

that we can form no. definite conception of its 

magnitude. 

The two most promising lines of quantitative 

attack upon the problem of elementary evolution are as follows: One begins with a study 

of the numerical relations between the atomic 

weights of the elements, and the other with 

attempts to determine the structure of the 

atoms. I cite these in their historical order, 

. which is not necessarily the one of greatest 

importance. The atomic theory was still in 

its infancy when in 1815 Prout suggested that 

all the atomic weights were whole numbers, 

based upon hydrogen as unity. Hydrogen, 

then, was the primordial element from which 

all others were derived. As most of the early 

detern1inations of atomic weight were rather 

crude and many of them close to integers, 

Prout's hypothesis was quite plausible. As the 

detern1inations became more exact it was 

found that few atomic weights were integral 

and that many of them differed widely from 

whole numbers. Prout's hypothesis was therefore set aside, although it has recently been 

revived upon a different foundation. 

Since the time of Prout numberless attempts 

have been made to trace relationships between 

the atomic weights, but only a few of them 

were of any scientific value. The subject was 

a favorite one for a certain class of speculators, . 

who generally started with preconceived opinions as to what atoms ought to be. Some 
56 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

interesting partial relations were pointed out 

by competent investigators, but the first advance of general significance was the reconstruc-

' tion of the entire scheme of atomic weights by 

Cannizzaro, which brought it into harmony 

with the law of Avogadro. In this new system 

the old chemical equivalent of oxygen, 0 = 8, 

became 0 = 16, the present standard of value. 

Definite relations between the atomic weights 

now began to appear which previously were 

unsuspected, and these found expression in 

the "periodic law" of Mendeleef and the 

Lothar Meyer curve of atomic volumes. In 

both generalizations the starting point was the 

same, and the atomic weights were arranged 

in the order of increasing magnitude, from 

hydrogen up to uranium; or, as we can say 

now, the order of their atomic .numbers, an 

expression . which has become significant only 

within very recent years. 

The periodic law, or periodic classification 

of the elements, is given in the following table. 

The atomic numbers precede the symbols of 

the elements, and the atomic weights are given 

below them. A different placing of the rareearth metals will be considered later. 

P eriodic table of the elements. 

[The upper numerals in the headings indicate natun.l groups; the lower numerals (arabic) indicate valencies. The rare-earth elements are 

inclosed within a thick line.] 

0 I II III IV v VI VII VIII 

0 +1 +2 +3 +4 -3-5 -2-6 -1-7 (a) 

~ 

lH 

1. 008 

2He 3 Li 4 Gl 5B 60 7 N 80 9F 

4.00 6.9 9.1 10.8 12.00 14.01 16.00 19.00 

lONe 11 Na 12Mg 13 Al 14 Si 15 p 18 s 17 Cl 

20.2 23.00 24.32 26.96 28.07 31.04 32.06 35.46 

18A 19 K 20 Cu. 21Sc 22 Ti 23V 24: Cr 25Mn 26 Fe 27 Co 28 Ni 

39.9 39.1 40.07 45.1 48 . 1 51.0 52.0 54.93 55.85 58.97 58.68 

29 Cu 30 Zn 31Ga 32 Ge 33 As 34 Se 35 Br 

63.57 65. 37 70.1 72.5 74.96 79.2 79.92 

36 Kr 37 Rb 38 Sr 39Y 4:0 Zr 41 Cb 42Mo 43- 44 Ru 45 Rh 46 Pd 

82.92 85.45 87.83 89.33 90.6 93.5 96.0 101.7 102.9 106.7 

47 Ag 48 Cd 49In 50 Sn 51 Sb 52 Te 53 I 

107.88 112.40 114.8 118. 7 121.7 127.5 126.92 

54:Xe 55 Cs 56Ba 57 La 58 Ce 

130.2 132.81 137.37 139.'0 140.25 I 

59 Pr 60Nd 61- 62Sm 63 Eu 64Gd 65Th 

140.6 144.3 150.4 152.0 157. 3 159.2 

66 Ds 67 Ho 68 Er 69Tu 70Yb 71 Lu 72~ 73 Ta 74 w 75- 76 Os 77 Ir 78 Pt. 162.5 163.5 167.7 168.5 173.5 175 181.5 184.0 190.9 193.1 195.2 

79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84b 85-

197.2 200.6 204.0 207.2 209.0 

8tJ Rn 87 - - 88 Ra su c 90Th 91 d 92 u 

222. 0 226.0 232.15 238. 2 

I 

a Valencies diverse. b Polonium? c Actinium? d Protoactinium? 

/ 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 57 

The significance of the foregoing table, of 

which there are many variants, is evident at a 

glance. The elements in each vertical column 

are closely allied, forming the natural groups 

with which all chemists are familiar. The alkaline metals, the series calcium, strontium, 

and barium, the carbon group, and the halogens are examples of this regularity. In other 

words, similar elements appear at regular intervals and occupy similar places. If we follow any horizontal line of the table from left 

to right we find a progressive change of valency, 

and in both directions we find a systematic 

variation of properties. Broadly stated, the 

properties of the elements, chemical and physical, are periodic functions of their atomic 

weights; and this is the most general expression of the periodic law. At certain points in 

the table gaps are left, and these are believed 

to co:rrespond to undiscovered elements. For 

·three of the spaces that were vacant when 

Mendeleef announced the law he made specific 

predictions, which, as has already been stated, 

were verified by the discovery of scandium, 

gallium, and germanium. Radium and the 

inert gases, much more recently discovered, all 

fall into their proper places in the table and 

give additional emphasis to its validity. 

Place No. 72 is undoubtedly to be filled by the 

recently discovered element termed hafnium 

or celtium, two names which are at present in 

controversy. The names assigned to Nos. 84, 

89, and 91 are provisional only and may not 

be sustained. The elements corresponding to 

Nos. 43, 61, 75, 85, and 87 are as yet unknown, 

although their properties can be predicted 

with a close approach to certainty. 

The periodic table is also very suggestive as 

regards the chemical relations and modes of 

occurrence of the elements in nature. In the 

first place, the members of the same elementary group have similar properties, form similar compounds, and give similar reactions, and 

because of these conditions they are commonly 

· found in more or less close association. Thus 

the platinum metals are seldom found apart 

from one another; chlorine, bromine, and 

iodine occur under very similar conditions; 

selenium is found in native sulphur; cadmium 

is extracted from ores of zinc; and so on through 

a long list of regularities. The group relations 

govern many of the associations that are 

.actually observed, although they are modified 

by the conditions that influence chemical 

union. Even here, however, regularities are 

still apparent. In combination unlike elements seek one another, and yet there appears 

to be a preference for neighbors of approximately equivalent mass. For example, silicon 

follows aluminum in the scale · of atomic 

weights, and in the crust of the earth silicates 

of aluminum are far the most abundant minerals. An even more striking example is furnished by the series oxygen, sulphur, selenium, 

and tellurium. Oxidized compounds of many 

elements are found in the mineral kingdom, 

but most of them are compounds of metals of 

low atomic weight. Above manganese, sulphides are abundant; but selenium and tellurium are more often united with the heavier 

metals silver, mercury, lead, or bismuth, and 

tellurium with gold. The elements of high 

atomic weight seem to seek one another, a tendency which is indicated in many directions, 

even though it may not be stated in the form . 

of a precise law. The general rule is evident, 

but its full significance is not · so clear. 

One phase of the periodic law, equally sug- · 

gestive with the preceding table, is shown in 

Lothar Meyer's curve of atomic volumes. 

When these volumes are plotted against the 

atomic weights they give a curve that consist_s 

of a series of undulations or waves of considerable amplitude. On these waves similar elements occupy similar positions-the alkaline 

metals at the crests, the heavier metals in the 

depressions, and the other elements in orderly 

arrangement between these extremes. The 

regularities are very striking and continue as 

far as the elements of the rare-earth group 

above cerium, where the waves flatten out, 

until at tantalum the curve becomes normal 

again. Similar curves can be · drawn for other 

physical properties of the elements, with similar results. Richards,4 for example, has superimposed upon the curve of atomic volumes 

curves representing compressibilities, coefficients of cubical expansion, and the reciprocals 

of the melting points. All four curves are 

similar in type and show the same periodicity. 

They are somewhat ragged, but nevertheless 

they tell the same story. The irregularities 

are due partly to defective data and partly to 

the fact that the physical constants were not 

4 Richards, T. W., Am. Chem. Soc. Jour., vol. 37, p.1649, 1915. 
58 SHORTER CONTRIBUTIONS TO Gl ~NERAL GEOLOGY, 1923. 

determined under strict~y . equivalent conditions. The atomic volumes, which are the 

ratios between the atomic weights and the 

specific gravities of the solid elements, are 

especially in need of revision. The specific 

gravities of some elements were determined at 

temperatures relatively near their melting 

points, those of others at temperatures 1,000 

or more degrees below them. It is possible 

that if all could be determined at points near 

the absolute zero, or, as an alternative, at 

points just below the temperature of fusion, a 

smoother curve might be given. 

The curve of atomic volumes, as given in 

Plate XXII, is reproduced, with the author's 

permission, from Professor A. W. Stewart's 

volume "Some physico-chemical themes" 

(London, 1922). In one respect it is likely to 

be misleading. The atomic volumes are calculated from the atomic weights, not from the 

atomic numbers. 

In the region of the rare-earth metals, between cerium and tantalum, the regular evolution of the elements seems to have been 

interrupted, so that a systematie periodicity is 

no longer evident. These metals all resemble 

one another very closely and form compounds 

of similar type. Their normal oxides are all 

of the form R20 3 , their chlorides are RC13, and 

so on, and they are therefore to be considered 

trivalent. Cerium, however, which is a member of this group, also forms a dioxide, and it 

is therefore possibly quadrivalent, although 

most of its compounds are of the trivnlent 

type. Tne earlier elements of the group, 

which appear in the periodic scheme-namely, 

scandium, yttrium, and lanthanum-are all 

normal. 

Furthermore, the rare earths occur in nature 

under similar conditions, they are almost 

everywhere intimately associated, they are 

difficult to separate, and their oxides are not 

easily reducible to metals. These very intimate relations need to be explained, and the 

curious flattening of the Lothar Meyer curve 

in the part of the atomic-weight scale which 

the rare-earth metals occupy gives us a clue 

to their mode of origin. It is evident . that 

they must have been formed under very similar 

conditions, which changed but slightly as the 

atomic weights increased. In other words, 

the conditions were nearly constant, but not 

quite, for with absolute constancy there would 

have been only one element generated instead 

of at least a dozen. 

The two preceding paragraphs lead at once 

to a very simple hypothesis. In the course of 

evolution from the hottest to the coolest stars 

there was probably a period of undeterminable 

duration when the rate of cooling and condensation was in some unknown way retarded, 

so that the conditions became nearly uniform. 

During this period, which was followed by one 

of increased activity, the elements of the rareearth group were formed. This hypothesis 

gives a rational explanation of the known 

facts concerning these elements and is therefore, despite its speculative feature, legitimate. 

If it is sound, then the elements of the rareearth series should appear in the periodic table 

as prolonging the trivalent group, and not be 

scattered under other groups to which they 

can not possibly belong. 5 

One more curiously suggestive relation connecting three distinct groups of . elements 

deserves consideration here. The halogens, F, 

Cl, Br, I, are strongly electronegative; the 

alkaline metals, Li, N a, K, Rb, Cs, are strongly 

electropositive; and these two groups are 

separated by the inert gases, He, Ne, A, Kr, 

Xe. So we have the following triads: F, Ne, 

Na; Cl, A, K; Br, Kr, Rb; I, Xe, Cs. The 

atomic weights in each triad are consecutive. 

Another probable triad is incomplete; only 

He and Li are known. One more electronegative element is needed here, which should 

be a gas of greater chemical activity than 

fluorine and of lower atomic weight. Is 

nebulium, with atomic weight near 2.7, the 

missing member~ If so its chemical activity 

might account for the nonappearance of its 

lines in the stellar spectra. · Was it used in 

building other elements~ That question I 

have asked already, but it is not yet answered. 

Here we enter the realm of pure speculation, 

the foundations of which are insecure. Specu- · 

lation is of value only in so far as it is suggestive. The intervention of the inert gases 

between two groups of great chemical activity 

is well established, but I must leave its explanation to physicists and mathematicians. 

Although the periodic classification of the 

elements is now thoroughly established, there 

5 In this mode of placing the rare-earth metals, I find that I have been 

anticipated by Dr. C. Renz (Zeitschr. anorg. allgem. Chemie, vol. 122, 

p. 143, 1922). My interpretation of the scheme is, I think, new. 
THE EVOLUTION AND DISINTEGRATION OF MATT'ER. 59 

are certain details of it that remain to be 

adequately investigated. The numerical relations between the atomic weights can not at 

present be discussed with any approach to 

finality. The problem is complicated by frequent changes-for example, within the last 

two or three years the atomic weight of 

scandium has been raised from 44 to 45, that 

of bismuth from 208 to 209, and that of 

antimony from 120.2 to 121.77. Recent investigations relative to "isotopes" have thrown 

doubt upon the definiteness of the atomic 

weights as they have been actually determined; 

and until that question is settled experimentally 

the true numerical relations must remain uncertain. The theoretical atomic weights will 

be considered later. 6 

Now, using the word in its chemical sense, 

let us ask: What is an atom? Here many 

loose reasoners have gone astray and have 

assumed that because atoms have been found 

to be decomposable, the atomic theory is 

overthrown. They seem to regard the etymological meaning of the word as having ultimate 

significance, but etymology is an unsafe guide 

in the discussion of scientific problems. The 

technical significance of p. word may be quite 

unrelated to its etymological history. What, 

for instance, does the word "chloroform" 

mean? According to etymology, a green ant! 

In brief, the chemical'atoms are now known 

to be complex, ranging from the comparatively 

simple hydrogen up to the highly complicated 

and unstable uranium. Each atom is supposed 

to consist of an electropositive nucleus, attended by one or many electrons of opposite 

sign. In the hydrogen atom there is one 

' ' planetary" electron, in helium two, and so 

on regularly up to 92 in uranium, at the present 

summit of the atomic-weight scale. These 

electrons are also supposed to be, above a 

certain small number near the beginning of 

the scale, arranged in rings or perhaps concentric shells around the nuclei. Whether 

they are revolving about the nuclei, like planets 

around the Sun, or are relatively at rest is an 

open question. Models that show the structure of atoms have been constructed, but they 

are not in complete agreement. The prevalent 

opinion regards each atom as resembling a 

6 For a very complete history of the periodic law, see Venable, F . P., 

The periodic law, Easton, Pa., 1896-a valuable contribution to the 

history of chemistry. 

miniature solar system, and the term "planetary 

electrons '' is used to distinguish those around 

the nucleus from some which have found place 

within it. The mass of an atom is almost 

entirely concentrated in the nucleus, for it 

is known that the weight of a single electron 

is only about rm of that of an atom of hydrogen, or 0.00054 on the ordinary scale of atomic 

weights. 

On this foundation Rutherford 7 has erected 

his scheme of elementary evolution,· starting 

with the hydrogen atom. The nucleus, or 

"proton," and the single electron are taken as 

the two fundamental constituents of all matter, 

whether element or compound, and these units 

are purely electrical. Prout's hypothesis has 

come to life again, but in a highly modified 

form. 

The next important step in the study of 

atomic structure was taken by Moseley,8 who 

from measurements of the X-ray spectra of the 

elements discovered relations which proved 

that "there is in the atom a fundamental 

quantity which increases by regular steps as we 

pass from one element to the next"-that is, 

the next in the ascending · scale of atomic 

weight-and that "this quantity can only be 

the charge on the central positive nucleus." 

That charge increases with increasing atomic 

weight and so follows the order of the elements 

upward, or in other words the order of the 

atomic numbers H 1, He 2, Li 3 Ca 

20, Zn 30, and so on up to U 92. These numbers are now regarded by many physicists as 

of more fund amen tal importance than the 

atomic weights from which they were first derived. In the series of atomic numbers, just 

as in the periodic law, there are gaps that represent undiscovered elements. There is no 

place in the scheme, however, for nebulium 

or coron1um. The atomic numbers may have 

to be revised. 

Now, without rejecting Moseley's "law," we 

must admit that the experimental evidence for 

it is incomplete. The region of the metals of 

the rare earths needs to be investigated, so as 

to determine whether their atoms carry electrical charges in the order demanded by the 

law. Does their anomalous character show 

itself here? The curious relations of the inert 

1 Rutherford, Sir Ernest, Nature, vol. 110, p. 182, 1922. 

s Moseley, H. G. J., Philos. Mag., 6th ser., vol. 26, p.1024, 1913; vol. 27, 

p. 703, 1914. 

PROPERT. OF U. S. U~: t!'J OF M!NES -~ 
60 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

gases, which have already been pointed out, 

also need explanation. The periodic variations 

in the physical properties of the elements also 

seem to require adjustment to the law. The 

difficulties thus suggested may be more apparent than real, but they should not be ignored. 

The question has often been asked whether 

the atomic weights of the elements are definite 

constants, or merely statistical averages of 

slightly differing values~ The actual determinations were made on masses of material containing millions of atoms, which may or may 

not be exactly alike but are tacitly assumed to 

be so. To state the problem in different form, 

what are the elements as we really know them ~ 

In a remarkable series of experiments Aston 9 

has obtained evidence, which he regards as 

proof, of the complexity of the atomic weights 

as determined by chemical methods. Powerful positive rays in a magnetic field were driven 

upon a number of elements, which then gave 

on photographic plates what he calls their 

" mass spec t ra. " Th ese spectra s h . ow hnes 

cor~esponding to whole-number atomic weights, 

which, with some exceptions, represent not 

the accepted values but some higher and some 

lower. The new lines, p.s interpreted by Aston, 

are due to" isotopes," and the elements yielding 

them are regarded as mixtures. The subject 

of isotopes I shall take up in the final section 

of this paper, whete it properly belongs. A 

few elements gave mass spectra of single lines, 

which nearly agreed with. the accepted atomic 

weights, and these Aston defines as "simple 

elements." 

From the evidence furnished by the mass 

spectra Aston concludes that all the true atomic 

weights, including the isotopes but excepting 

hydrogen, are whole numbers. This rule he 

regards as fundamental, although it is based 

on 0 = 16 as the standard of values. But this 

standard was originally adopted as a matter 

of convenience and had at first no theoretical 

foundation. It seems, therefore, as if its importance is overrated. Nevertheless we may 

assume the validity of the rule and see how 

nearly the atomic weights of some of the 

"simple elements" conform to it. That is, 

How far do the real atomic weights diverge 

9 Aston, F. W., Isotopes, London, 1922. In this volume Aston gives 

a complete summary of his own researches, together with much material 

relative to Rutherford's work, Moseley's law, the periodic system, and 

related subjects. 

from the theoretical whole numbers ~ The 

figures are given in the following table: 

Atomic weight. 

Divergence, 1 

Theo- Found. retical. 

part inGlucinum ........ ______ 9.018 9.0 500 

Nitrogen .... _ .. _ .. _____ 14.008 14.0 1,750 Aluminum ........ _____ 26.963 27.0 730 

Phosthorus _ ...... _____ 31.04 31.0 773 Sulp ur ________________ 32.06 32.0 540 A rsen1 . c ... _ . _____ .. _____ 74.96 75.0 1,875 Iodine. _ ....... _ . _ . ____ 126.92 127.0 1,588 Caesium ........ ________ 132.81 133.0 700 

These divergences are too large to be ascribable to experimental errors. The poorest of 

the atomic-weight determinations cited above 

is probably correct within 1 part in 3,000, and 

that of nitrogen is trustworthy, I think, within 

1 part in 10,000. I base my opinion on a careful study of the methods by which each value 

was determined and especially on their concordance. 

That the real and the ideal rarely coincide is 

well shown in the preceding tab~e, and I venture to cite two well-known examples of such 

disagreement. Avogadro's law, that equal volumes of gases under equal conditions contain 

equal numbers of molecules is rigorously applicable only to ideally perfect gases. To the 

real gases with which we have to deal the law 

applies approximately and is subject to correction by the two small constants discovered · by 

Van der Waals. The law of electrolytic dissociation is true· only for infinitely dilute solutions, and solutions of that kind do not come 

within our experience. Under working conditions it may be nearly true. Now, if the 

whole-number rule for the atomic weights is 

theoretically sound, a supposition which is not 

yet proved, we may have to assume a distinction between perfect and imperfect elements, 

and for that assumption there is some justification. Uranium, as we know it, has been 

slowly decomposing for millions of years, and 

the uranium that remains is partly decayed. 

The atomic weight of the normal element as it 

was before decay began is quite unknown. 

Thorium offers a similar example, and it is furthermore very doubtful whether any thorium 

exists that is quite free from ionium of certainly lower atomic weight. In short, the 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 61 

radioactive elements are probably all imperfect in the same way. Are any other elements defective? That we can not say, unless 

we attempt to define a perfect element. Such 

an element should be absolutely stable and 

therefore undecomposable, and only the primal 

protyle would satisfy these conditions. Hydrogen is the simplest known form · of matter, 

but is there nothing simpler? We do not 

know. 

In Rutherford's scheme of elementary evolution he uses the hydrogen nucleus with its 

single electron as a primary unit, and helium, 

with four protons and two electrons, as a 

secondary unit. From hydrogen and helium 

nuclei and electrons the complex nuclei of all 

the other atoms are supposed to be built up. 

A system s~milar to this has been developed by 

Harkins, 10 who assumes another hypothetical 

unit of mass 3, composed of three protons and 

two electrons. This new unit may be equivalent to nebulium, but that is by no means 

certain. The system, however, works well 

and brings out some interesting relations 

between the atomic weights, which may be 

partly real and partly coincidental. Rutherford seems to neglect nebulium, and neither 

he nor Harkins takes into account coronium, 

of unknown atomic weight. Its possible importance, however, ought not to be ignored. 

Coronium surely exists and must play some 

part in the evolution of matter. In Nicholson's scheme of elemental evolution 11 coronium, 

nebulium, and a hypothetical protofluorine 

are utilized and given atomic weights. That 

of coronium is assumed to be a little more 

than half that of hydrogen. 

So far the views of Rutherford and Harkins 

are in essential harmony with the astronomical 

evidence. Hydrogen and helium are two 

primary units from which other elements were 

developed, but in the electrical theory an 

assumption is made to which an alternative 

hypothesis is possible. The helium nucleus is 

supposed to be built up from four hydrogen 

nuclei or protons. But He= 4, and H = 

1.0078; so that 4H is really 4.0312, or slightly 

less if the loss of two electrons is deducted. 

A loss of mass in forming helium is therefore 

assumed and is explained by an electromagnetic theory of "packing." For this 

1o Harkins, W. D., Phys. Rev., 2d ser., vol. 15, pp. 73, 141, 1920. 

u Nicholson, J. W., Philos. Mag., 6th ser., vol. 22, p. 864, 1911. Coronium and nebulium are also taken into account by Rydberg (Jour. 

chim. phys., vol. 12, p. 585, 1914). 

33372°-25-5 

explanation, which is not very clear, I must 

refer to the publications of Rutherford and 

Aston already cited. 

Suppose now that helium instead of being 

a quasi polymer of hydrogen is really an 

independent entity of mass 4. This supposition may not be in complete agreement 

with the electrical theory of matter as that is 

now formulated, but it is sustained by some 

evidence. Hydrogen is chemically active, 

helium is inert, and it is not easy to see how 

four atoms of the one could coalesce to form 

an atom of the other. In the nebulae the two 

elements appear to be widely separated, with 

no suggestion of any other relation between 

them than that of a possible common ancestor. 

Furthermore, the . alpha ray of radioactive 

transformations is an atom of helium, which 

shows no sign of further decomposition. A 

priori the now hypothesis is jlJ,st as plausible as 

the other, although neither is completely 

proved. That the alleged loss of mass is not a 

necessary assumption seems to be clear. In. 

the formation of compounds there is no 

indication of any "packing effect," although 

there may be very great condensation. 

It is in the highest degree probable that 

hydrogen and helium are two fundamental 

elements in the evolution of matter. But 

nebulium should be considered with them as 

having some part, if only a subordinate one, 

in the evolutionary system. From the position 

of its lines in the spectrum of the great nebula 

of Orion, Fabry and Buisson, by interferometer 

measurements, found its atomic weight to be 

2.7, or almost exactly 2j. Now, the atomic 

weights of several other elements, taken as 

whole numbers, are even multiples of this 

figure and also of the atomic weight of helium. 

From a much larger list I select the following 

atomic weights for comparison with that of 

nebulium and with one another; Helium, 4; 

oxygen, 16; magnesium, 24; sulphur, 32; calcium, 40; titanium, 48; iron, 56. Five of 

these elements, it will be remembered, are 

those which appear earliest in the hotter stars. 

Now, with nebulium (Nm) = 2j, the comparison 

is as follows: 

3 Nm= 8=2He 

6 Nm=l6=4He=0 

9 Nm=24=6He 

12 Nm=32=8He=2 0 

15 Nm=40=10He 

18 Nm=48=12He=3 0 

21 Nm=56=14He 
62 SHORTER CONTRIBUTIONS. TO GENERAL GEOLOGY, 1923. 

Regarded superficially the foregoing figures 

are very suggestive, but they must not be 

taken too seriously. They may, perhaps, 

express approximate relations, and they show 

that nebulium deserves consideration in any 

scheme of atom building. It is, however, an 

unruly element, for it disturbs the order of 

atomic numbers, and its atomic weight is not 

integral. The latter irregularity is not serious, 

for five of the elements in the table have atomic 

weights that diverge appreciably from whole 

numbers. Whether the divergences indicate 

mixtures of isotopes remains to be seen. The 

table as it stands is an excellent example of the 

ease with which the theorist can find relations 

between the atomic weights if he is only allowed 

to take a few little libertie~ with the facts. 

Two other sets of figures approximating 

atomic weights are worth citing here. Whole 

numbers are assumed, and the symbols represent the atomic weights: 

Fe=28i=4N ==i8Li=l4He 

Mo=2Ti=38=4Mg=60=80=24He 

These relations are very striking, but have 

they any real significance relative to the 

evolution of the elements ~ If we were to 

arrange 92 integers, taken at random between 

the atomic weights of hydrogen and uranium, 

and as nearly as possible equally spaced, 

should we not be likely to find many numerical 

relations between them ~ In short, is not the 

proble~ of the atomic weights something more 

than a mere numerical exercise~ This question, 

I think, needs no answer. If many of the 

chemical atomic weights are merely "statistical averages" of two or more isotopic values, 

any attempt to discover exact mathematical 

relations between them will surely be futile. 

Since the · discovery of radioactivity atomic 

genealogists, if I may call them so, have been 

extremely busy. Their contributions to the 

literature of the subject are very numerous, 

and I can not undertake to summarize them 

here. Some of their publications are worthless, and some are extremely valuable, but 

nearly all are more or less one-sided, for they 

lay undue stress upon mathematical or physical 

or chemical data, and each writer . ventures 

little out of his own special field. Not until all 

lines of evidence have been brought into convergence . can the problem of elementary 

evolution be solved. The workers in different 

fields and with different outlooks rnust learn 

how to cooperate. 

In every attempt that has heretofore been 

made to explain the evolution of the elements 

in detail there are difficulties which must be 

faced. Some of these difficulties have already 

been considered. The integrity of the atomic 

weights has been called in question, and the 

deviation of many of them from whole numbers 

has not been satisfactorily explained. The 

theory of atomic numbers is· also incomplete, 

for it makes no allowance for possible elements 

simpler than hydrogen, or between hydrogen 

and helium; and it reverses the observed order 

of three pairs of elements, namely, potassiumargon, nickel-cobalt, and iodine-tellurium. 

That these reversals are justifiable is by no 

means certain. The positive evid~nce should 

not lightly be set aside. 

In the last analysis the problem of elementary evolution seems to be one of equilibria, or, which is much the same thing, of 

relative stabilities; and the fundamental 

data are those which relate to atomic structure. On this subject there is as yet no general 

agreement, but the scheme that has been most 

favorably received is that developed by 

Rutherford and his colleagues, to which I have 

already referred. , 

At first sight Rutherford's scheme of evolution appears to be very simple and symmetrical, 

but it is by no means free from difficulties, and 

some of these lie at its very foundations. 

The light electron and the massive proton are 

defined as "atoms of negative and positive 

electricity"; but what these definitions mean 

is not clear. As the elements above helium 

are developed the nuclei or groups of protons 

become more and more complex, and just how 

the protons are held together is unexplained. 

The uranium atom is supposed to carry 92 

electrons, and this complexity of structure 

accounts for the recognized instability of that 

element, as shown by the constant emission of 

helium from its nucleus, the very swift alpha 

rays. Between hydrogen and uranium the 

elements are arranged in the order of their 

atomic . numbers, which represent not only 

the number of electrons in each atom but also 

the net electric charge carried by its nucleus. 

But what is meant by an electric charge upon 

an "atom" or cluster of " atoms" of electricity ~ Is there not something in the proton 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 63 

that is not electrical, which serves as the car- Now, in terms of atomic structure, what does 

rier ~ These questions I can not attempt to this reaction mean~ How was it that three 

answer. They involve the fundamental hy- elementary molecules could be disrupted and 

pothesis that matter and electricity are identi- two new ones formed~ Each hydrogen atom is 

cal, which is certainly not proved. supposed to consist of a nucleus with one elecOne more doubtful feature of Rutherford's tron, and each oxygen atom of a nucleus with 

system remains to be noticed. It is assumed eight electrons. What are these electrons 

that the progression . from the simplest to the doing, and what is the nucleus of the new molemost complex element is regular and unin- cule of water~ Why does condensation take 

terrupted, step by step. But the irregularity place, and why is heat emitted~ Is the loss of 

shown by the rare-earth elements in the peri- heat due to an arrest of motion of two or more 

odic system seems to have been ignored, and this electrons~ Moreover, by electrolysis the whole 

must be taken into account in any valid scheme reaction can be reversed and the original equiof elementary evolution. libria reestablished. These questions are as 

In what I have said so far I have not intended · yet unanswered, and they raise the larger 

to be hypercritical. It seemed necessary to question as to the nature of chemical affmity. 

point out some of the difficulties that exist in If the theory of atomic structure is sound it 

all the schemes of elementary evolution, for to should ultimately shed some light upon these 

ignore them is to put obstacles in the way of problems. 

progress. There is really more to be said in Let us go a step further and consider a more 

favor of the current theories of atomic structure complicated case, one of double decomposition. 

than can be urged against them. All of them When solutions of barium chloride and sodium 

are attempts to interpret evidence, and each sulphate are mixed the following reaction 

one is partly successful. Their agreements are occurs: 

more significant than their differences. 

A scientific theory has two sides, one specu-

. lative, the other utilitarian. As a mere 

intellectual exercise it has little importance; 

·its real value is in its ability to classify phenomena, to express their relations, and to point the 

way to new discoveries. In plain language, 

Does it work~ If the prevailing theory of 

atomic structure is fundamentally sound it 

must satisfy these conditions. Hitherto it has 

been developed almost entirely in its physical 

and mathematical aspects; its chemjcal aspects 

have received too little consideration. It is on 

the chemical side that the theory is likely to be 

most severely tested. The complete study of 

any chemical reaction involves problems that 

are difficult to solve. 

A chemical reaction may be described in a 

general way as a readjustment of equilibria. 

Let us consider one of the simplest, the formation of water from its elements as represented 

by the equatwn 

2H2 + 0 2 = 2H20 

Here three stable· molecules are broken up, and 

two new stable molecules are formed; heat is 

generated, and three gaseous volumes are condensed to two. A further condensation to 

liquid water follows. 

BaCl2 + N a2SO 4 = BaSO 4 + 2N aCl 

Here we have five kinds of atoms and four 

different molecules, but three of the molecules 

are partly dissociated in solution. The barium 

sulphate, however, is thrown down in solid 

form, and the reaction is not reversible. All 

the problems suggested by the simpler reaction 

appear in this new equation, with others that 

are equally difficult to answer. What part 

does water play in this double decomposition~ 

Why is the barium sulphate condensed to a solid 

from diffused ions in the initial solution~ What 

are all the electrons doing, and what are the 

nuclei of the four compounds~ I suspect that 

we are a long way from any complete answer 

to these questions. A theory of atomic structure, to be satisfactory to chemists, must give 

them some clear conceptions regarding the 

mechanism of chemical reactions. 

Examples like these might be multiplied 

indefinitely, but all give rise to similar problems. 

In every case, if we accept the electric theory 

of matter, we must ask the same questions: 

What are the electrons doing, and how are the 

protons held together~ If for the moment we 

confine our attention to the evolution of the 

atoms, we have also to consider the conditions, 

external and internal, that determine their 
64 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

relative stability. The external conditions 

have already been defined; the internal conditions are those of a~omic structure, its simplicity or complexity, the symmetry of the 

atom, and the exact electrical balance between 

electrons and nuclei. A simple, symmetrical 

atom is likely to be very stable; a complicated 

structure implies instability. The terms stable 

and unstable are of course relative; they have 

no absolute meaning. 

In the study of elementary evolution two 

basic problems underlie all the others. What 

is the process, and what are its products~ 

Unfortunately we are unable to reproduce the 

process artificially. We can not hope to 

build up · elements as they are built up in the 

stars, for the conditions are too severe for us 

to meet. We can, however, tear down some 

of the more complex structures and so get some 

light upon their genesis. That work is now 

· just beginning, and from it we may rea.sonably 

expect to arrive at wore definite conclusions. 

The products of devolution we can study 

directly, and the two lines of evidence ought 

ultimately to converge. 

I venture now to point out one analogy that 

may have some significance with regard to the 

character of the elements. Organic chemistry 

is defined as the chemistry of carbon compounds, and atoms of carbon, in chains or 

rings, form the skeleton, or framework, or 

scaffolding of the whole edifice. May not the 

elements be built in a similar way with atoms 

of helium instead of carbon~ This suggestion 

is not altogether new: it is implied in the hydrogen-helium scheme of evolution; but here it 

would include nebulium as a possible part of the 

superstructure. It is at least worth testing, 

although I am not blind to possible difficulties 

in its detailed application. 

In all discussions relative to cosmogony 

there is a danger of going too fast and too far. 

That statement holds true in the present discussion. We know that the same elements 

appear throughout the stellar universe,· and 

we must assume that their evolution was 

governed by the same fundamental laws of 

chemistry and physics. But we can not assume that all solar systems are exactly like 

ours in chemical composition. The parent 

nebulae may have differed in the relative proportions of their component gases, and the· 

rate of cooling in passing from nebula to star 

was not necessarily everywhei'e the same. 

It is conceivable, therefore, that different solar 

systems may have generated the elements in 

somewhat different order, and not invariably 

in the same relative abundance, but these dissimilarities, if they exist, are probably not very 

large. To assume that anything like absolute 

uniformity exists would, however, be quite 

unwarranted. 

Before we pass on to the subject of the evolution of compounds, it seems well to consider 

briefly a question relative· to what may be 

called scientific utility. A scientific theory, 

to be useful, must meet the conditions that 

have been stated in a former paragraph and 

so prove its value. Such a theory is the atomic 

theory of Dalton, which is the corner stone 

of modern chemistry. Even the modern electrical conception of matter is based upon it. 

Many examples of similar purport might be 

cited. 

It has recently been asserted by high 

authorities that "a chemical element is defined by its atomic number." How far is this 

conception sustained by the test of its utility~ 

How far can it be used in dealing. with chemical 

problems~ May it not be better to say that a 

chemical element is defined by the aggregate 

of all its properties~ The theory of atomic . 

numbers covers only part of the ground. . 

The atomic numbers, it should be remembered, assign to each element its place in the 

order of ascending atomic magnitude. That is, 

the atomic weights came first, and the atomic 

numbers followed. It is now held, however, 

that the atomic numbers also represent the · 

electric charges carried by the nuclei of the 

atoms, and the number of electrons belonging 

to each one. These claims may be valid, but 

they have not yet been as thoroughly tested 

as they should be. Will they guide future 

research and "be fruitful in discoveries~ That 

remains to be seen. 

In practical utility the atomic weights are 

far more important than the atomic numbers. 

They are the fundamental quantities of chemical arithmetic and are in constant use in 

chemical calculations. To the working chemist they are indispensable. In the calculation 

of analyses, or of the proportions in which 

substances shall be taken in order to perform 

a given quantitative reaction, atomic weights 

are always, directly or indirectly, employed. 
THE EVOLUlON AND DISINTEGRATION OF MATTER.. 65 

They are expressed in every chem!J.cal formula artificial synthesis, and they ' are not decomand in every chemical equation, ant the atomic posable by any of the ordinary processes of the 

numbers can never replace them The laws chemical laboratory. The reported decompoof chemical combination are bas d upon the sition by means of powerful radiations or by 

combining numbers of the element , and these electrical currents of the greatest intensity 

are the atomic weights. In the p riodic table will be considered in another section of this 

the atomic weights and the ato ic numbers memoir. Compounds, on the other hand, are 

both appear; but the periodicity of physical formed by the combination of elements, into 

properties is best shown in curveslike that of which they are easily separated and from 

atomic volumes. Such curves sh w that the which many of them can be prepared synphysical properties of the elements are periodic thetically. The terms element and compound 

functions of the atomic weights. The alleged are used here in their ordinary technical sigsupremacy of the atomic numbers is by no nificance and are not subject to any verbal 

means established. The usefuln~ss of the quibbling. The elements form one definite 

atomic weights is independent o the order class of substances, the compounds form 

in which they are arranged. another, and the chief difference between 

After all, the physical quantiti s that are them is one of · stability. 

directly related to the atomic n mbers are Between the formation of an element and 

functions of the atomic masses, an so, too, are the formation of a compound there is, however, 

the atomic numbers. another difference. The first stage of the 

That the theories of atomic str~ture which process was one that re_quired a vast period of 

have so far been proposed are ot in close time; the second stage is marked by rapidity. 

·agreement has already been pointe out. One The series of elements was slowly formed, and 

partial theory, however, deserv .s mention their rate of decay, as shown between uranium 

here-that of .the tetrahedra. 1 carbln atom as and lead, is also relatively slow. The formaadvanced independently by Van't off and by tion and decomposition of compounds, on the 

Le Bel. That theory was framed in order to other hand, is rapid; and for some compounds 

account for the different optical properties of the rate is measurable. The distinction is not 

the two tartaric acids, but it didf1 uch more absolutely definite, for some of the short-lived 

than that. It was the foundatio of stereo- products of radioactive decay seem to be exchemistry, a new field of research, which has ceptions to the rule, which in general may be 

been . wonderfully fruitful in im~prtant dis- stated as follows: The process of evolution is 

cover!es. The theory was dev1r,ed before characterized by progressive acceleration, beelectrons were known, but it is e1idently ad- ing slow at first and becoming gradually more 

justable to the electronic conceptio:q. of matter. and more rapid. Its rate of acceleration may . 

No such adjustment is needed, However to not be uniform, but its general drift is clear. 

emphasize its proved efficiency. ~ It follows the line from the simplest subNoTE.-For. a critical summary of the pri cipal theories stances to the most complex. In all vital 

of atomic structure see Stewart, A. W., orne physico- processes the ease and rapidity with which 

chemical themes, pp. 373-397, 1922. See also Webster, compounds are formed and developed is eviD. L., and Page, L., Nat. Research Cou~il Bull. 14, dent, and some of these substances are ex1921. 

THE EVOLUTION OF COMPOU DS. tremely complicated. 

Just as an infinite number of words can be 

. It has already been said that th1 process of formed from the 26 letters of the alphabet, so 

evolution is continuous, from t e simplest myriads of compounds can be built up from 

forms of matter to the most co plex. Be- comparatively few elements. At least a huntween elements and compounds here is no dre.d thousand compounds are already known, 

sharp line of demarcation, and one lass shades but by far the greater number of them are 

into the other. In one sense the e~ments are artificial products and have no place among 

really composite, primary compoun s built up the relatively simple substances that are 

from a few fundamental substance ·, and they developed in a cooling globe. In that !aboare characterized by great relati stability. ratory the possibilities of combination are 

They have so far not been form d by any limited. We have already seen that bands 
66 SHORTER CONTRIBUTIONS TO GENERAL GEO~OGY, 1923. 

of a few compounds, such as the oxides of 

carbon and possibly cyanogen, have been detected in the spectra of the cooler stars and 

the Sun, but these compounds are all gaseous. 

Heavy, solid compounds would probably sink 

below the reversing layer and not be recognized in the spectrum. Can we decide, with 

any approach to probability, what solid compounds would be likely to be first formed 

under the conditions of a cooling globe? 

The answer to this question is simple. The 

most stable compounds would come first, and 

they are such as appear among the products 

of the electric furnace. Carbides, silicides, 

phosphides, borides, and nitrides are all stable 

at very high temperatures, and such compounds with iron, nickel, or · manganese as 

bases are substances- of high specific gtavity 

and would be likely to sink deeply into the 

cooling mass. At the surface of the Earth 

and probably througho.ut the lithosphere they 

would cease to exist, for water, especially in 

the form of superheated steam, transforms 

them into other compounds, such as hydrocarbons, oxides, silicates, phosphates, borates, 

and salts of ammonium. Water must have 

been a compound to appear at an early stage 

in the process of evolution, and it is one of 

the principal reagents that were and are active 

in determining the composition of the Earth's 

crust. 

This speculation, which is not extravagant, 

receives some support from the study of volcanic emanations, of which carbon dioxide and 

ammonium chloride are common constituents. 

Hydrocarbons in small amount are also found 

among volcanic ejectamenta. The existence 

of bpron nitride within the Earth is suggested 

by the association of boric acid and ammonium 

compounds in the Tuscan fumaroles and at 

other well-known localities. Boron nitride is· 

a very stable compound; but when heated in 

a current of steam it yields boric acid and 

ammonia. As for silicates and oxides, they 

are the chief constituents of the lithosphere. 

The silicates would be easily formed by oxidation of the primary silicides, but only the 

simpler compounds, such as constitute at 

least nine-tenths of the present lithosphere, 

would appear at first. Their crystallization 

and segregation could take place only in the 

cooling of a fused magma. On this point 

their artificial syntheses are conclusive. From 

such a magma the primitive crust of the Earth 

was formed. 

A variety of processes, some physical and 

some chemical, must have taken part in the 

solidification of the planet; but their effects 

could hardly have been symmetrically distributed. The temperature of the cooling 

mass was certainly ·not uniform. Whenever 

new compounds were formed heat was generated, the local temperature rose, and inequalities of composition were brought about 

by diffusion. Where the temperature at the 

surface of the globe was lowest there solidification began. At such points new chemical 

reactions became possible through contact 

with the gases and vapors of the primeval 

atmosphere·. Just what the composition of 

that atmosphere may have been we do not 

know; but it must have contained oxygen, 

carbonic acid, and water, . three powerful reagents, with possibly some of the stronger acids 

also. 

Throughout the cooling. process and indeed · 

throughout the process of evolution from 

nebula to planet, gravitational energy was at 

work distributing the various forms of matter 

according to their density. In the Earth we 

have a heavy, probably metallic nucleus, surrounded by a zone of the denser silicates 

grading upward into lighter compounds, and 

after them a relatively thin shell of sediments 

and other decomposition products. Then 

comes the hydrosphere, and surrounding all 

the atmosphere. These zones are of course 

not sharply separated but interpenetrate one 

another to a greater or less extent. V olminic 

effusions, for example, break through the 

sediments, and locally reverse the· primary 

gravitational arrangement, which, after all, is 

what might be called an irregular regularity. 

The broad outlines of the process are clearly 

discernible in spite of local blurring. 

This zonal structure of our planet, due to 

gravitational adjustment, has been of great 

significance in fixing the conditions upon 

which terrestrial compounds could be formed. 

It is commonly supposed that the Earth is 

analogous to a huge meteorite, having a nucleus 

consisti~g principally of ilickel-iron with some 

inclusions of free carbon and a few simple 

compounds. This supposition will be considered in detail in the next section of this 

memoir; if it is correct then the nucleus of the 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 67 

Earth, or centrosphere, is essentially a region 

of almost no chemical activity. It is protected from the outermost zones of actiye 

reagents by the intervening shells of igneous 

silicate rocks, which are easily modified by 

aqueous and atmospheric agencies and in less 

degree by volcanism. To cite two familiar 

examples of such changes magnesian rocks are 

converted into talc and serpentine, and feldspathic rocks are kaolinized. In short, on 

passing from the centrosphere to the surface 

of the lithosphere, the chemical changes become more and more varied and complex. 

Through them the sedimentary rocks were 

formed, and in the later stages of the Earth's 

history living organisms also played an important part in the production of limestone, 

dolomite, and marine phosphates. Leaving 

minor details out of account we may say that 

the general conditions governing the evolution 

of natural inorganic compounds seem to be 

fairly well understood, even though we know 

very little of the inner mechanism of the many 

reactions in which combinations and decompositions proceeded simultaneously. In the 

geologic history of the Earth's crust the more 

important of the chemical changes are easily 

traced. The artificial syntheses of many 

minerals also give us much information upon 

the problem of inorganic evolution. 

At the surface of the Earth, when its crust 

was sufficiently cool, the evolution of compounds entered upon a new field of ·activity. 

Organic compounds were formed, and they 

furnished the material basis for the evolution 

of living beings. Organisms, each capable of 

reproducing its kind, became physically possible. This faculty of reproduction is something 

that sharply distinguishes living from nonliving matter. · 

The probability that carbides and nitrides 

were among the earliest compounds to form 

in a cooling globe has already been pointed 

out, and also that these compounds, by hydrolysis, yield hydrocarbons and ammonia. Calcium carbide yields acetylene, which easily 

polymerizes into benzene, from which a long 

list of other hydrocarbons can be derived. 

The carbides of aluminum, glucinum, and 

manganese give methane, CH4 ; those of the 

rare-earth metals yield mixtures of acetylene, 

methane, and ethylene, and from some of them 

liquid and solid hydrocarbons are also derived. 

From uranium carbide Moissan 12 obtained a 

mixture of liquids, consisting largely of olefines 

with some members of the acetylene series 

and some saturated compounds. Hydrogen is 

also set free in some of these reactions.13 

If now, by reactions such as have just been 

described, hydrocarbons and ammonia were 

formed from compounds contained in the 

primitive magma, a first step was probably 

taken toward preparing the surface of the 

Earth for the advent of. living organisms. 

From metallic phosphides phosphine, the 

analogue of ammonia, would be generated, and 

it· would quickly be oxidized, yielding phosphates. Among the substances that appear 

in volcanic emanations there are hydrogen 

sulphide, sulphur dioxide, carbonic acid, and 

hydrochloric acid, compounds which might all 

be formed simultaneously with the hydrocarbons. Add to these the gases of the atmosphere, and we shall have assembled much 

of the raw material that is essential to the later 

upbuilding of organic tissue. But between 

magma and protoplasm there is a vast gap, 

which science has not yet bridged. The evolution of compounds has not stopped, but our 

knowledge of its course is interrupted. 

The moment we enter the field of biochemistry we encounter problems of great 

complexity. Innumerable new compounds appear, especially in the tissues of plants, and 

some of them are extremely complicated. 

Many of these compounds, however, can be 

isolated and analyzed. We can determine 

their composition and measure their physical 

properties, but how they were developed in the 

growing plant is a question that is rarely 

answered even in part. One group of examples 

will serve to show how complex the problems 

really are. 

One of the most marvelous of chemical laboratories is . contained within the seed capsule 

of the opium poppy, Papaver somnijerum. In 

that small inclosure a juice is secreted which 

when dried, solidifies to that extremely complicated mixture opium. In opium about 

thirty different compounds have been identified, including more than twenty distinct alka12 Moissan, H.,Compt. Rend., voL122,p.1462, 1896. SeealsoDamiens. 

M.A., Annales dechimie, 9thser., vol.10, p. 137, 1918, on the carbides of 

the cerium group. 

n For a summary of the literature relating to the inorganic syn1!heses 

of hydrocarbons, and especially from the carbides contained in cast 

iron, see Chrke, F. vV., The data of geochemistry, 4th ed.: U.S. Geol. 

Survey Bull. 695, pp. 730-732, ·1920. 
68 SHORTER CONTRIBUT.IONS TO GENERAL GEOLOGY, 1923~ 

loids, of which morphine, C17H19N03, is the In animal matter, which consists almost 

most abundant but not the most complex, entirely of proteids, the complexity is even 

although, as we see from its formula, each mole- greater than in plants. Plants may contain ·a 

cule contains forty atoms. How many pro- much larger number and variety of definite 

tons and how many electrons are there here, crystallizable compounds, but in animal tissues 

and what are they doing 1 the proteids predominate, and they are of many 

But this is not all. The capsule also con- different kinds. Into this subject I can not go 

tains the seeds from which other plants can be at length, but I may be permitted to ask one 

grown, and in each plant within a single season question. Is the morphological or structural 

this complex of chemical syntheses is begun increase in complexity from the lowest to the 

and completed, and so on generation after highest forms of life accompanied by a corregeneration. The seeds are rich in oil but not sponding change in the complexity of chemical 

in alkaloids; it is at the summit of their growth constitution 1 This aspect of evolution has, I 

that these very complicated substances appear. think, never been seriously considered, but it 

Suppose now that on this same acre of ground surely deserves attention. To show its signifiwith the poppy are sown the seeds of a dozen cance I venture to offer the following illustra-

. or more plants. Each one will be, in a certain tion, which is based upon an elaborate study 

sense, a synthetic chemist, working out its own of. the inorganic . matter of marine invertespecial set of reactions . . A tobacco plant will brates: 14 

form nicotine, mustard will generate an "oil" In some of the lowest forms of life, as in the 

rich in sulphur, some species will produce diatoms, radiolarians, and siliceous sponges, 

hydrocarbons such as terpenes, while others the skeletal matter consists chiefly of opaline 

will specialize in forming sugar or starch or silica, a very simple substance. The stony 

strong acids. All are nourished by the same corals are built up from calcium carbonate, 

soil, the same water, and the same atmosphere, which is slightly more complex. The echinobut each one breeds true to type and never derm skeletons also contain magnesium carmakes a mistake in its chemistry. Does each bonate, and the shells of some brachio'pods 

seed contain some directive principle that consist mainly of calcium phosphate. The 

guides its germination and growth 1 To say shells of the higher crustaceans, such as the 

that the seeds differ in composition, which is lobster, are still more complicated. With a 

quite true, may give a partial answer to this large proportion of organic matter, proteid in 

question; but it does not explain the vital character, they contain both carbonates and 

factor, the capacity of each plant to reproduce phosphates of calcium and magnesium. The 

its kind. progressive increase in complexity is clearly 

Up to a certain point the evolution of com- evident. It also appears in the bones of the 

pounds within these different plants follows higher mammals. In them we find organic 

similar lines. All generate the vegetable fiber substances, such as gelatin and fats, but also 

that is, so to speak, the fabric of their skeletons, carbonates of calcium and magnesium, with a 

and all produce chlorophyll, the principal col- very large proportion of calcium fluophosoring matter of their leaves. I use the term phate. The question that was asked in the 

chlorophyll in its general sense, although this preceding paragraph is surely pertinent, and 

substance is usually if not always commingled it receives the beginning of an answer here. 

with other compounds of similar character. A complete answer, however, will involve some 

Here a new reagent becomes of supreme influ- serious discriminations, and it must also recogence-namely, radiant energy, the energy of · nize the fact that we are now considering prodthe Sun's rays. It is only by means of this ucts and not processes. The two fields of invesreagent that chlorophyll can form. Are some tigation must, of course, be studied together, 

of the other syntheses also dependent upon it 1 but the distinction between them. is clear. A 

Albuminoids and proteids are also produced, physiological process is a complex of chemical 

and in these colloid substances chemical com- combinations and decompositions, of evoluplexity probably reaches its limit. They are H See Clarke. F. w·., and Wheeler, W. C., U. S. Geol. Survey Prof. 

the essential constituents of protoplasm. Paper 124, 1922. 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 69 

tions and devolutions, and the two sets of and a nunber of other minerals, all of aqueous 

phenomena are quite distinct, even though origin, that are found in beds of salt. The 

they always appear together. The one is the researches of Van't Hoff and his colleagues 

complement of the other. The physiological upon the Stassfurt 'salts are especially suggesprocesses of the higher animals -are surely more tive. The compounds associated with the salt 

complicated than those of lower forms. were not only prepared synthetically, but the 

For example: In respiration we inhale oxy- temperature at which each one formed was 

gen and exhale carbonic acid, which is produced also determined, giving datum points in what 

by the consumption of organic tissue. The has been called a "geological thermometer." 

formation and renewal of the tissue is a case Similar temperature relations have been disof true evolution, to ·which our question covered for other minerals, such as the silica 

properly relates; the rejected waste or excre- group and wollastonite, and they give valuable 

tory products can for present purposes be dis- information as to the conditions under which 

regarded. We are considering the products the rocks containing them were deposited. In 

of grow.th, not those of decay. The discrim- short, the chemical processes that took part in 

ination may sometimes be difficult, but it terrestrial evolution are being revealed experishould never be ignored. The alkaloids of mentally. The literature of synthetic mineralopium, for instance, are waste products and ogy is very voluminous, but these few exrepresent the downward path of chemical amples are all that need to be cited here. 

change. Their citation here, however, serves They serve to illustrate the methods by which 

to illustrate the wonderful complexity of the some problems of evolution a:re being solved. 

processes that are involved in the growth of What has been said relative to the syntheses 

plants. of inorganic compounds also applies, but with 

The formation of any new compound, serious limitations, in the organic field. Many 

whether simple or complex, natural or artificial, substances that are found to exist in living oris an item in the scheme of chemical evolution. ganisms have been made artificially, but by 

Under natural conditions many well-known methods that are surely not identical with 

compounds are incapable of existence; some are those followed by plant or animal. In life 

destroyed by even moderately high tempera- many syntheses are effected simultaneously 

tures; others are decomposed by the action of and rapidly; in the laboratory the conditions 

water; and still others, like the fulminates, are are quite different. The chemist starts with 

easily exploded by percussion or friction. All · pure material and builds his compounds indithese inhibitions are evaded or controlled by a vidually and slowly, but his results are never-

. skillful chemist, who can regulate tempera- theless of great significance, even though they 

tures and pressures and can establish for each may not be directly applicable to the interprecompound the environment in which it can tation of vital ph~nomena. There is, however, 

form. He can also work with pure materials, a partial correlation, which is better than none 

which are rarely found under natural condi- at all. 

tions. The artificial compounds help us to This is no place for an essay on biochemistry, 

a better understanding of those which exist which may be described as the dynamic side of 

in nature, and this can easily be shown. physiology. All living organisms, ~onsidered 

Many of the minerals that form the solid apart from their psychological relations, are 

crust of the Earth have been reproduced syn- dependent upon a complex of chemical changes, 

thetically by methods equivalent to those fol- some products of which are utilized and. others 

lowed by nature. The species that are char- rejected as waste. In the digestion of food 

acteristic of the igneous rocks, such as the feld- many of these changes have been traced, and 

spars, pyroxenes, and olivine, originate in a great variety of compounds take part in 

molten magmas, and artificial magmas yield them. Some of the compounds, especially the 

the same compounds. Quartz may be either proteids, are broken down into simpler forms; 

magmatic or crystallized from aqueous solu- and their derivatives are distributed each to 

tions, and both modes of origin can be copied its proper place in the organism. The motive 

in the chemical laboratory. Artificial lime- power that effects their distribution is thermostone is easily prepared, and so too are gypsum chemical in origin and is measured in term~ of 
70 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

calories. Finally, new proteids are formed, 

and wasted tissues are regenerated; and this is 

true chemical evolution. The evolution of the 

Earth's crust and the evolution of living tissue 

are parts of the same line of growth from the 

simplest to the most complicated forms of matter. The line, however, is not straight but one 

with many branchings. 

water of the great oceans, and its use here 

makes a liberal allowance for the saline matter, 

such as beds of salt, that are found in the 

crust of the Earth. For present purposes they 

are negligible . quantities. If the salts of the 

Ocean were gathered into one solid block, they 

would have a volume of at least 4,800,000 cubic 

miles, or enough to cover the entire United 

States to a depth of 1.6 miles. The fresh 

THE RELATIVE ABUNDANCE OF THE CHEMICAL waters of our globe are also negligible, for a 

ELEMENTS. quantity equivalent to 1 per cent of the Ocean 

One of the most obvious facts in chemistry would cover all the land areas to a depth of 

is that some of the elements are very abundant 200 feet. Even the mass of Lake Superior 

and others extremely rare. It is also easy to becomes relatively insignificant. The mass of 

see that this distinction is definitely related to the atmosphere, so far as it can be determined, 

the conditions under which the different ele- is equivalent to that of 1,268,000 cubic 1niles 

ments were generated. The simplest and most of water, the unit of density. Combining these 

stable ones were formed at the highest tempera- figures, we have for the composition of known 

tures and in the greatest abundance; the most terrestri~l matter about 93 per cent of solid 

complex elements appeared last of all· and in crust, with 7 per cent for the Ocean. The 

the smallest quantities. The original nebula proportion assignable to the atmosphere is 

was a finite mass of matter, and the scarcer only 0.03 per cent, which may be regarded as a 

elements represent the material left over after small correction to be applied when needed .

15 

the more common ones had been formed. We are dealing with the relative abundance of 

How far do these conclusions harmonize with. the different forms of matter and not · with 

the observed facts~ absolute quantities. Quantitative accuracy is 

In an attempt to answer this question we not attainable. 

must recognize certain limitations. An almost What, now, is the composition of the acinfinitesimal portion of the matter that forms cessible part of the lithosphere~ Neglecting 

the solar system is all th9,t is available for the thin film of organic matter upon its surdirect quantitative investigation. Only .· the face, we need only consider two classes of 

Ocean, the atmosphere, and a very thin outer rocks, the igneous and the sedimentary. · 

shell of the Earth's crust are accessible to us. Metamorphic rocks are merely the result of 

As for the Ocean and the , atmosphere, their alterations of one or the other of these two · 

composition is well known; that of the rocky and may be left out of account. Such inclushell is less easily ascertained. sions as beds of coal or metallic ores are inIn order to determine the average composi- significant in quantity as compared with the 

tion of known terrestrial matter we must first vast mass of rocks now under consideration, . 

fix the relative proportions of its three com-~ which is, as nearly as can be determined, 95 

ponents. For this purpose let us asswne that per cent igneous and 5 per cent sedimentary. 

the crust of the Earth to a depth of 10 miles is The method by which these figures were obessentially like the average rock of its surface, tained, together with the average composition 

of the 't'ocks which we know and can analyze. of the sediments, I have given elsewhere.16 

The volume of such a crust, including the As it is impossible to analyze the 10-mile 

mean · elevation of the continents above the crust as a whole, we must do as well as we 

sea, is 1,633,000,000 cubic miles, with a prob- can by the method of sampling-that is, we 

able density of about 2. 7 to 2.8. must take samples of igneous rocks, the parThe volume of the Ocean is approximately ents of the others, from as many different 

302,000,000 cubic miles, although some au- localities as possible, and then average the 

thorities give slightly higher figures, and its . . density is a little below 1.03. This is the 15 ForthedetailsofthiscomputationseeClarke,F.W.,Thedataof 

geochemistry, 4th ed.: U.S. Geol. Survey Bull. 695, pp. 22-33, 1920. 

maximum density found by Dittmar in the 1s Idem, pp. 29-32. 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 71 

analyses. Thousands of such analyses have 

been made for petrologic purposes and are 

now available for use. The material came 

from all quarters of the globe, and the anq,lyses 

that are considered trustworthy have been 

assembled by H. S. Washington in .a monument~! volume. 17 From the data given by 

him 5,159 analyses rq,ted as ''superior" have 

been taken and averaged together, giving a 

fair conception of the mean composition of the 

igneous rocks.

18 

Now, omitting details, which can be found 

in the publications already cited, let us consider the significance of the following averages. 

The first column of figures gives the mean 

composition of 5,159 igneous rocks, stated in 

terms of elements and in percentages. The 

last column gives the average obtained by 

including accepted values for the sediments, 

the ocean, and the atmosphere, or in other 

words the mean composition of all known 

terrestrial matter to an assumed depth of 10 

miles below sea level. 

Average composition of igneous rocks and of all known 

terrestrial matter. 

~illc~~~: .·: ·. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Aluminum ......... . ............. . Iron ............................ . Calcium ......................... . Sodium .......................... . Potassium ... . ........... .. . . .... . 

~~~~i~:~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Phosphorus . . .................... . Hydrogen .................. . .... . Manganese ...................... . Chlorine ............. . ...... . .... . Carbon ......................... . Minor constituents ... . .......... . 

a Oceanic. 

b In limestone. 

1 2 

46.41 

27. 58 

8. 08 

5. 08 

3. 61 

2.83 

2. 58 

2. 09 

. 72 

.157 

.129 

.124 

. 096 

. 051 

. 463 

100. 00 

49. 19 

25. 71 

7. 50 

4. 68 

3. 37 

2. 61 

2. 38 

1. 94 

. 648 

.142 

. 872 

.108 

a. 228 

b. 139 

. 473 

100.000 

These figures show that eight elements form 

97.38 per cent of all known terrestrial matter, 

17 Washington, H. S., Cnemicalanalyses of igneous rocks, 1884 to 1913: 

U.S. Geol. Survey Prof. Paper 99, 1917. 18 A detailed critical discussion of the method of averaging and the 

results obtained is to appear in Professional Paper 127 of the Geological 

Survey, by Clarke and Washington, now in press. An abstract of the 

averages was published in the Proceedings of the National Academy 

of Sciences for May, 1922. 

leaving only 2.62 per cent for all the others. 

The influence of the Ocean and the atmosphere 

is very slight, and with a thicker mass of igneous 

rocks it would be still smaller. In the Earth 

as a whole the Ocean would amount to only a 

small fraction of 1 per cent and therefore be 

negligible. 

In many of the published analyses of igneous 

rocks figures are given showing appreciable 

:hut small percentages of some of the scarcer 

elements. The average amounts are as follows: 

Barium ....... 0. 081 Nickel. ....... 0. 031 

Sulphur. . . . . . . 080 Fluorine...... . 030 

Chromium.. . . . 052 Copper. . . . . . . . 010 

Zirconium..... . 051 Lithium...... . 005 

Vanadium..... . 041 Zinc. ......... . 004 

Strontium..... . 034 Lead.......... . 002 

Several attempts have been made to determine the composition of the Earth as a whole, 

all based upon its supposed similarity to a huge 

meteorite. The mean density of the Earth is 

nearly double that of its crust, and it behaves 

like an enormous magnet. Hence the assumption has been made, to which I have already 

referred, that its central portion is metallic and 

consists largely of iron. How far is this 

assumption justifiable~ 

To answer this question let us begin with the 

chemical composition of known meteorites. 

These extraterrestrial bodies are divided into 

two classes, meteoric stones and meteoric irons, 

which, however, are not sharply distinct. 

Nearly all the stony meteorites contain more or 

less iron, and many of the others contain stone. 

For instance, the pallasites are masses of iron, 

with something like the texture of a sponge, 

in which the cells are filled with nodules of 

olivine. Again, the meteoric shower that fell 

at Estherville, Iowa, in 1879, contained masses 

of stone and many smaller masses of iron. 

These were all, of course, components of the 

original meteor. For the average composition 

of 99 meteoric stones we have the following 

~omputa6on by Merrill. 19 The first column 

of figures gives the actual average; the second 

is recalculated to 100 per cent after rejecting 

the admixed nickel-iron, sulphides, and phosphides. 

19 Merrill, G. P ., Am. Jour. Sci., 4th ser., vol. 27, p. 469, 1909. Another 

average, by 0. C. Farrington, appears in Field Columbian Mus. Pub. 

151, 1911. It is in fair agreement with Merrill's. 
72 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

A verage composition of meteoric stones. 

Silica .......... . ................ . Alumina ................ . .. . ..... . Ferrous oxide ......... . ..... _ . .... . Lime ...... . ............ . ........ . Magnesia._ ........ _ ... _ .... . .... . 

Soda ......... . ....... . . . ........ . Potassa ................ . .......... . Manganese oxide. __ .. _._._ ... _ .... . Chromi te ... _ ... _ . _ . _ ............. . Nickel, including cobalt. ... _ .. _._ .. Metallic iron._ ... ___ ......... _ . __ . Sulphur . .... ___ _ . ___ ......... _ ... . 

Phosphorus . . _ ................... . 

Found. 

38.98 

2. 75 

16.54 

1.77 

23.03 

.95 

. 33 

. 56 

. 84 

1. 32 

11. 61 

1. 85 

.11 

100.64 

Recalculated. 

45.46 

3.21 

19. 29 

2.06 

26.86 

1.11 

. 38 

. 65 

. 98 

100.00 

Some of the analyses show small amounts of 

copper, tin, carbon, etc., which need not be 

considered here. The average stone is essentially a peridotite and therefore quite different 

from the average terrestrial rock. A great 

deficiency in feldspars is evident, and they 

form nearly 60 per cent of the 10-mile shell of 

the lithosphere. There is little or no free silica 

indicated by the figures. That the meteorites 

were originally in a state of fusion is also clear, 

for the dominant mineral, olivine, is formed 

only in that way. The same is true also of the 

glass, which is a common constituent of 

meteoric stones. 

It is by no means certain that the average 

given in the foregoing table represents with 

any accuracy the mean composition of all 

known meteoric stones, of which many were 

never analyzed. Even these meteorites form 

but a trifling fraction of the vast number that 

must have fallen unseen. Some doubtless fell 

in the ocean, and others in deserts or forests, 

never to be found. Nevertheless the average 

is not without value, when it is considered in 

relation to other data. As for the individual 

stones that are represented in the average, 

they show great differences in composition. 

A very few, of which Juvinas and Stannern 

are typical, consist mainly of augite and 

anorthite, with very little nickel-iron. The 

Bishopville stone is nearly pure enstatite. 

These stones are exceptional; in by far the 

greater number of known falls pyroxen~s and 

olivine are the dominant minerals, with variable proportions of nickel-iron. The transition from stone to iron is very gradual. The 

very common 9hromite of meteoric stones is 

invariably associated with magnesian minerals, iron, and nickel-the same association 

that is found in terrestrial rocks. Oldhamite, 

calcium sulphide, is only known as a meteoric 

mineral; it dissolves in water and rapidly 

hydrolyzes, therefore it can not long exist 

except in anhydrous surroundings, and all our 

igneous rocks contain small amounts of water. 

One very small group of meteoric stones 

deserves to be considered separately-the carbonaceous meteorites. The type and extreme 

example of these is the one that fell at Orgueil, 

France, in which Pisani found 13.89 per cent 

of water plus organic matter, which consisted 

essentially of hydrocarbons. Such a meteorite 

could reach the surface of the Earth only under 

very exceptional conditions. The chances are · 

that its organic matter would be burned soon 

after it entered the atmosphere, and its stony 

portion disintegrated and scattered as dust. If 

so the atmosphere must receive accessions of 

carbon dioxide that would have a distinct 

influence upon plant life and would perhaps 

account, in part at least, for the carbon that is 

·locked up in coal and petroleum. This, I 

admit, is pure speculation, but not without 

some plausibility. A cometary origin of these 

meteors is probable, for hydrocarbons are 

shown in the spectra of comets, and several 

instances are known of periodic showers of stars 

that have followed the paths of periodic comets 

which have disappeared. Biela's comet is one 

which after repeated returns is now represented 

only by a starry shower. We can not, however, 

assume that all meteors are the remains of 

comets. There is, as will be seen later, strong 

evidence to the contrary. 

The average composition of meteoric iron is 

more easily determined than that of meteoric 

stone. The one consists mainly of an alloy of 

nickel and iron; the other is a mixture of different silicates. The irons contain, in minor 

proportions, several other substances, such as 

troilite, FeS; schreibersite, a phosphide of iron 

and nickel; daubreelite, FeCr2S4, the sulphide 

corresponding to the chromite of meteoric 

stones; lawrencite, FeCl2 ; cohenite, (FeNiCo) 3C; 

graphitic carbon; and in the iron of Canyon 

Diablo, minute diamonds. Diamond is also 

found in the meteoric stone of Novo Urei. 

Carborundum, CSi, is also reported by Moissan 

as present in the Canyon Diablo iron. Nodules 

of troilite and of graphitic carbon are common, 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 73 

some of them as large as a hen's egg; the other 

inclusions are diffused in smaller amounts. Of 

these the lawrencite is in one way the most 

conspicuous, although it is rarely seen in distinct masses. On exposure to moisture it is 

hydrolyzed, forming basic chlorides and releasing hydrochloric acid, so that its presence 

is too often manifested by the tendency of an 

iron to rust and ultimately to fall to pieces. 

Everyone who has had much experience in 

handling collections of meteorites knows how 

troublesome this obnoxious compound is. It 

is very difficult to stop its ravages. It is not 

improbable that much of the chlorine in the 

ocean came originally from lawrencite. Was 

the primeval ocean strongly acid ~ The question is legitimate, even if it can not be definitely 

answered. Some of the oceanic chlorine is 

undoubtedly of volcanic origin, and that may 

have had its source in lawrencite. We do not 

know the facts but may be permitted to suppose. One thing is certain-namely, that the 

permanence of a meteoric iron depends upon 

, the amount of ferrous chloride which it contains. 

At Ovifak, in Greenland, and at several 

neighboring localities, native iron is found 

which was at first thought to be of meteoric 

ong1n. It is now known to be terrestrial iron, 

brought up in some manner from below, 

together with the basalt in which it is embedded. Some of it is in small grains and 

some in large masses of several tons in weight, 

and it resembles meteoric iron in every essential particular. It contains some lawrencite, 

and also carbon, which is combined with iron, 

probably as cohenite. The presence of a carbide was proved by George Steiger in the laboratory of the United States Geological Survey. By heating some of the Ovifak iron 

with ammonium chloride he obtained a mixture of hydrocarbons, both saturated and 

unsaturated. 

For the average composition of meteoric 

iron and its terrestrial equivalent we now have 

the following data: First, the average of 318 

analyses of meteoric iron, as computed by 

Farrington 20 ; second, the average of 13 analyses of the Greenland iron, cited by Dana.21 

In the analyses of Greenland iron figures· for 

silica and insoluble matter have boon rejected 

!o Op. cit. 

21 System of mineralogy, 6th ed., pp. 28, 29, 1914. 

as representing impurities taken up from the 

adjacent rocks. 

Average composition of meteoric and native iron. 

Meteoric. 

Iron ................... _________ . 90. 85 

Nickel. ________________ ._________ 8. 52 

Cobalt ___ .. _. ___ . _____________ . _ . . 59 

Copper _________ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 02 

Sulphur __________ .__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 04 

Carbon. ____ ____________________ ... . 03 

Phosphorus. ______ .. ______________ .17 

Chlorine _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _____ .. __ Chromium ____ . ______________ __ .. _ . 01 

100.23 

Terrestrial. 

92.53 

2.20 

. 62 

. 23 

. 28 

1. 78 

. 21 

. 06 

97.91 

These averages, although they differ somewhat, do so no more than individual analyses 

of meteoric iron. No two irons are precisely 

alike. The absence of chlorine from the first 

column of figures merely means that it was 

not determined, and the same is true with reference to chromium in the second column. 

Analyses of rocks and minerals differ widely as 

regards completeness. 

In one way the analyses of meteoric irons are 

likely to be slightly misleading. They represent clean, bright samples of the nickel-iron 

and take no account of the large inclusions of 

graphite, troilite, and the inore · generally 

diffused ferrous chloride. The composition of 

the entire mass of an iron would be unlike that 

of the selected metal, and the inclusions might 

amount to several per cent. No good estimate 

can be made of their average quantities. The 

averages given in the table, therefore, represent only approximate orders of magnitude, 

but the percentages of the minor constituents 

are certainly not large. 

That the minerals of the meteoric stones 

were originally in a state of fusion seems to be 

clear. Was the meteoric iron also molten~· 

This question can be answered in the affirmative, for the following reasons: 

In the preceding section of this paper it was 

shown that carbides and phosphides were 

among the compounds that would be the 

earliest to form in a cooling globe. Both carbides and phosphides are found in meteoric 

iron, and the even more significant sulphides 

also. Furthermote, troilite and graphitic carbon are often found in large nodules that could 
74 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

hardly have segregated except from a fluid or 

semifluid mass. The diamonds of the Canyon 

Diablo iron tell the same story. The artificial 

diamonds obtained by Moissan were produced 

by dissolving carbon in molten iron and cooling 

under great pressure. Finally, the highly 

crystalline structure of meteoric iron points to 

the same conclusion. No artificial iron shows 

that peculiarity. All the evidence points in 

. one direction, and the similarity of origin of 

stones and irons seems to be almost beyond 

doubt. Both stones and iron were formed in a 

cooling globe which in structure resembled 

the cooling Earth. This theory as to the origin 

of meteorites is the only one that is supported 

by positive evidence; all others are purely 

speculative. The theory is not original with 

me. It was advocated by Meunier and others 

and has .since been fully discussed by Farrington, 22 who has made use of much the same 

evidence as I have cited here. He also calls 

attention to the fact that meteoric stones 

sometimes show indication of strains and of 

brecciated structure, similar to corresponding 

features that are common in the crust of the 

Earth. Farrington's a,rguments in support of 

his thesis seem to be incontestable. 

The lines of evidence used by Farrington in 

his argument have recently been made much 

stronger hy the study of a meteoric stone that 

fell at Cumberland F'alls, Ky., on April9, 1919. 

This stone, which has been thoroughly investigated by Merrill,23 is made up of two distinct 

types of meteorites. The larger part is white 

and consists mai~ly of enstatite with a little 

diallage. It contains, however, inclusions of a 

black stone, made up of olivine and enstatite. 

There are also some scales of graphite, with a 

very little nickel-iron and troilite. The most 

noteworthy feature of the stone is that the 

white portion, instead of being comparatively 

homogeneous, is a breccia, a mass of sharply 

.angular fragments, which could be formed only 

by crushing the rock under great pressure or 

by grinding. The only interpretation that can 

be given to these facts is that the meteorite is a 

fragment of a much larger mass, of what may 

be called subplanetary dimensions-one large 

enough for the same processes to operate 

that are recognized in the rocks of the Earth . 

. How and when that planetoid was disrupted 

we do not know, and speculation upon that 

22 Farrington, 0. C., Jour. Geology, vol. 9, p. 630, 1901. 

.23 Merrill, G. P., U.S. Nat. Mus. Proc., vol. 52, p. 97,1920. 

subject would be out of place in this paper.24 

Its chemical composition, however, as shown 

by the analyses of meteorites, must have 

closely resembled that of the Earth. 

To complete the analogy between the Earth 

and the broken planetoid we should be able to 

calculate the percentage composition of the 

latter. This, however, can. not be done, for 

much of the meteoric matter is lost. In the 

catastrophe that destroyed the planetoid its 

lighter, outer shell was probably scattered in . 

dust, or in fragments so small that few of them, 

even if they reach the Earth, could ever be collected and identified. No granitic meteorite 

has yet been found, and the only distinctlyfeldspathic meteorites are those of the Juvinas and 

Stannern types, in which the feldspar is anorth;.. 

ite. Alkali feldspars occur in meteorites in very 

small and relatively unimportant proportions. 

The suggestion that the outermost portion of 

the planetoid was lost is not altogether imaginative. It is supported by the well-known phenomena that attend the fall of a large meteor. 

These are a brilliant light and a violent explosion, with a noise which has· been compared to 

thunder or the firing of heavy artillery. The 

meteor is also followed by a train of sparks as 

seen by night, or one of "smoke" in daytime. 

An explanation of these phenOJnena was put 

forth by Maskelyne 25 in 1862, about as follows: The meteor, coming from the cold of outer 

space, enters the atmosphere of the Earth with 

something like planetary velocity. By atmospheric friction its surface is almost instantly 

heated to incandescence; this portion of course 

expands and breaks away from the central 

mass with explosive violence. In this way the 

meteor is disrupted, and the fragments that are 

thrown off are seen in the trail of sparks or 

smoke which follows the falling mass. This 

explanation of the phenomena is very simple 

and seems to be satisfactory. The meteoric 

stone has just the composition which would 

result from the process described above. Its 

lighter surface has been blown away, and only 

the denser, interior portion of different composition has fallen to the ground. -

So far the evidence seems to be conclusive 

that the meteorites are fragments of a mass of 

24 T. C. Chamberlin (Jour. Geology, vol. 9, p. 370, 1901), regards meteorites as fragments of a planetoid which was tom to pieces by near 

approach to a larger mass. 

2~ Maskelyne, N. S., British Assoc. Adv. Sci. Ann. Rept., 1862, pt. 2, 

p.18S . 
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THE EVOLUTION AND DISINTEGRATION OF MATTER. 75 

matter which in composition closely resembled mean composition of the lithosphere there are, 

· the Earth. Of the dimensions of that mass we then, three averages to be combined, as follows: 

know nothing, except that it must have been · First, the average for the surface rocks; second, 

large enough to maintain its integrity at first that of the basalt; and third, that of the meteoin a fluid state, and that after it had solidified ric stones as given by Merrill. In this comcrustal movements occurred which produced bination the minor constitu~nts are discarded, 

the peculiar structures of meteoric stones. Its as representing small corrections that can be 

disruption took place long ago, how long we can applied when it is desirable to do so. The innot say; and many, perhaps the greatest num- completeness of the meteorite analyses renders 

her, of its fragments reached the Earth shortly- the omission necessary. The three sets of figafter the catastrophe. Of course we can not ures, given equal weight, appear in the followassume that there was only one such mass; ing table, together with their mean, the comthere may have been more than one, but that position of the lithosphere. 

question is not germane to the present discussion. The known meteorites show clear indications of a common origin; whether from one 

or two planetoids we need not ask. 

From what has been said so far, it is clear 

that the Earth was once a fluid mass, in which 

as it cooled the iron separated from the silicates 

just as it does from the slag in a blast furnace. 

The solid Earth, then, consists of two components-a nucleus of metallic nickel-iron and an 

envelope of silicate rocks. This conclusion is 

by no means new. It has been adopted by 

many other writers, and especially by Wiechert,26 whose argument is based on geodetic 

data. For the composition of the nucleus we 

have Farrington's average of 318 analyses of 

meteoric iron, which, . however, is subject to 

correction for its inclusion of other substances. 

What, now, is the average composition of the 

lithosphere~ 

For the composition of the lithosphere we 

have that of the igneous rocks near its surface 

and that of the stony meteorites, which are 

supposed to represent the material closest to 

the central iron. Between the two, the top 

and bottom of the lithosphere, there is a wide 

gap, which can be filled only hypotheticallythat is, by making probable or at least plausible assumptions. In the first place we may assume that between thelighterrocksatthesurface 

and the heavier at the bottom there is a fairly 

regular gradation, from an average andesite 

above to a peridotite below. In this hypothesis an average basalt may be assumed to fill the 

gap, without much risk of serious error. For 

the composition of the basalt we rp.ay use the 

average of 161 analyses as computed by Daly,27 

but reduced here to elementary form. For the 

26 Wiechert, E., Gesell. Wiss. GHttingen Nachr., 1897, p. 221. 7 Daly, R. A., Am. Acad. Proc., vol. 45, p. 211, 1910. 

Average composition of the lithosphere. 

Surface Meteoric The 

Basalt. litho- rocks. stone. sphere. 

O_xygen .............. 46.72 44.28 42.16 44.38 

Sll1con ......... -..... 27.76 23. 27 21.21 24.08 

Aluminum ........... 8.13 8. 44 1. 70 6.09 

Iron .................. 5.12 8.87 15.25 9.75 

Magnesium .. ~ ....... 2.10 3.76 16.12 7.33 

Calcium ............. 3.64 6.49 1. 48 3.87 

Sodium .............. 2.86 2.34 . 82 2.01 

Potassium ....... _- ... 2.60 1. 28 . 31 1. 39 

Titanium ............. . 73 . 83 .................... .52 

Manganese ........... . 12 25 .50 .29 

Phosphorus .......... .16 .19 .12 

Chromium ............ .06 -·------- .45 .17 

100.00 100. 00 1100. 00 100.00 

It will be noticed that in thi'3 average the 

nickel-iron of the meteoric stones does not appear. It is included in the total amount of 

metal which is required to bring the density of 

the Earth up to 5.5. 

Here we may venture to use a cunous analogy to which Wiechert has called attention.28 

Astronomers are generally agreed that the 

Moon was originally thrown off from the 

Earth. If so, its composition should be essentially like that of the lithosphere. Its mean 

density, 3.34, is that of some meteoritic olivines. 

That density, however, is too high for the stony 

portion of the lithosphere and suggests that 

the Moon contains, like the meteoric stones, 

some nickel-iron. The average meteoric stone, 

according to Merrill's calculation, contains 

nearly 15 per cent of nickel-iron, sulphides, and 

phosphides. The average density of 78 meteoric stones, as computed by me, is 3.54, a value 

that fits in well with the figures given above. 

2s Wiechert, E., Deutsche Rundschau, vol.132, p. 376, 1907. English 

translationin Smithsonian Inst. Ann. Rept., 1908, p. 431. 
76 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

To the stony matter alone of the lithosphere a 

probable density of 3.2 may reasonably be 

assigned. 29 That of the surface crust is .about 

2.8. For the density of the metallic nucleus 

the figure 7.8 is commonly assumed, but it may 

be a trifle too high. No allowance is made for 

inclusions of lighter material, but a density of 

7. 7 would probably be a minimum. The mean 

density of the Earth, as given by different 

authorities, lies somewhere between 5.5 and 5.6. 

With the data now at h1;1nd we can compute, 

at least approximately, the composition of 

the Earth as a whole and the relative abundance of the elements in the solar system. 

Wiechert 30 has already shown that the iron 

nucleus of the Earth and its rocky envelope 

are roughly equal in volume. If we assign 

to the Earth and its two components the 

respective densities of 5.5, 7.8, and 3.2 this 

relation holds exactly, and no probable changes 

in these values will greatly modify Wiechert's 

conclusion. Whatever permissible values we 

assign to the densities the two volumes will 

approach equality. The variations will not 

exceed 3 per cent in either direction-that 

is, for a little more iron and a little less rock, 

or vice versa. From the volumes and the 

densities the relative masses of the two components of the Earth can be determined, and 

then Farrington's average composition of 

meteoric iron and that of the lithosphere can 

be combined together. This combination has 

already been attempted by Farrington,31 but 

with the three densities taken as 5.57, 7.8, 

and 2.8. Here the figure for the density of 

the Earth is probably too high, and that of 

the lithosphere certainly too low. For the 

composition of the Earth by weight they give 

73.6 per cent of free metals and 26.4 per cent 

of rock. With the densities 5.5, 7 .8, and 3.2 

the percentages become 70.75 and 29.25, 

respectively. Considered as representing orders 

of magnitude, and we can expect nothing 

more, these two estimates are not very far 

apart. In the following combination the two 

percentages are rounded off to 71 and 29. 

Farrington's combination, however, differs 

from ours· not only in the assumed densities 

but also in assigning to the composition of 

the lithosphere that of its 10-mile crust. The 

two combinations are not comparable. 

29 Wiechert (op. cit., 1907), gives a density of 3.4. In his earlier paper 

he adopts the value 3.2. 

ao Wiechert, E., Gesell. Wiss. Gottingen Nachr., 1897, p. 243. 

s1 Farrington, 0. C., Field Columbian Mus. Pub. 151,1911. 

Average composition of the Earth; 

Nickel- Litho- The 

iron (71 sphere (29 Earth (100 

per cent.) per cent.) per cent). 

~i~k~~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~!: ~~ Aluminum........ . . . . . .. .. .. .. .. 6. 09 

Iron.................... 90. 64 9. 75 

NickeL................. 8. 51 ........ .. Cobalt.................. .58 ........ .. ·Magnesium............ .. .. . .. . .. 7. 33 

Calcium. . . . . . . . . . . . . . . . . . . . . . . . . 3. 87 

Sodium... . . . . . . . . . . . . . . . . . . . . . . . 2. 01 

Potassium . .. . .. .. .. .. . .. . .. .. .. . 1. 39 

Titanium... . . . . . . . . . . . . . . . . . . . . . . . 52 

Manganese.............. .. .. .. .. .. . 29 

Phosphorus ........... · . . 17 . 12 

Chromium.............. . 01 .17 

Sulphur, carbon, copper. . 09 (?) 

100. oo 1 100. oo 

12.77 

6.98 

1. 86 

67.20 

6.04 

.41 

2.13 

1.12 

. 58 

.39 

.15 

.08 

.16 

.07 

.06 

100.00 

It needs no argument to show that these 

figures have no claim to anything like :finality 

and that their value depends upon the assumptions that underlie the calculations. The 

fundamental assumption, which rests upon 

pretty definite evidence, is that the original 

mass of which the meteorites are fragments was 

similar in composition to the Earth and was 

formed in the same way. 

The second assumption, that the Earth contains a nucleus composed mainly of nickel-iron, 

surrounded by a stony envelope, is sustained 

by the facts that the Earth behaves like a 

huge magnet and that its mean density is 

about double that of the surface rocks. The 

application of these facts to the problem in 

hand involves subordinate assumptions as to 

the relative densities of the nucleus and the 

lithosphere. No probable change in the figures 

assigned to these densities can make any great 

change in the orders of magnitude as given in 

the table. The relative order of abundance 

will be the same, with iron first, oxygen second, 

silicon third, and so on. As for the scarcer 

elements, those which do not appear in the 

table, their total amount can not much exceed 

1 per cent, and their inclusion would make 

only insignificant changes in the percentages 

assigned to the really abundant substances. 

After making all reasonable allowances for the 

scarcer elements, we can say that ten of the 

more abundant ones, all below 60 in atomic 

weight, make up at least 99 per cent of all 

·terrestrial matter. T~ey are among the simplest and therefore the most stable elements 

and were formed in the largest quantities. 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 77 

This rule., as has been shown already, is re- matter within the Earth as set forth below is 

vealed by the evidence furnished by the stellar highly probable. 

spectra. At the center of our planet we should have a 

Whether all the members of the Solar Sys- rather ragged spheroid, with no well-defined 

tern are precisely alike in composition is and margin, consisting mainly of nickel-iron. Near 

must remain a matter of conjecture. It is its surface the metal would assume the pallasite 

conceivable that the outer planets may be type and begin to show inclusions of stony matsomewhat richer than the Earth in the lighter ter, principal~y olivine. This material would 

elements, such as aluminum, magnesium, cal- gradually shade into silicate rocks containing 

cium, and the alkali metals. On the other large inc}usions of free metal, and so on, step by 

hand, the Sun may be richer in iron. If that step, until the lighter feldspathic rocks began 

supposition is correct, then the inner planets to appear. These rocks, as the analyses show, 

should approximate an average composition contain little or no nickel-iron, and that presand represent the entire system. This hypoth- ent occurs in very small, sometimes almost 

esis, of course, can neither be proved nor dis- imperceptible grains. The condition thus outproved. Definite evidence is lacking. · lined is exactly what we should expect to reFrom the analyses of meteoric stones we can suit from the slow cooling of a molten globe. 

obtain some additional suggestions as to the The heavier substances should gravitate to the 

distribution of matter within the Earth. In center, followed in order of density by the 

one of Farrington's papers,32 which I have lighter substances. The evidence at our disalready cited, he has tabulated 125 analyses of posal seems to warrant the conclusions drawn 

meteoric stones, classified according to the from it. We are dealing, however, with probquantitative system. One analysis falls in the abilities, not with proofs. 

salfemic class, 9 are dofemic, and 94 perfemic. From the evidence presented in the precedThe classes persalane and dosalane are entirely ing pages some additional conclusions may be 

missing, for they belong to the destroyed sur- drawn. If the Earth consists of a solid nucleus 

face of the wrecked planetoid. Now, these of nickel-iron, surrounded by an envelope of 

analyses show a distinct gradation in the silicate rocks in equal proportions by volume, 

amounts of nickel-iron which the stones con- what is the diameter of the one and the thicktain. The few feldspathic meteorites, those ness of the other~ For the sake of simplicity 

that were nearest the surface of the parent we may assume ideal conditions, as follows: 

mass, contain little or no nickel-iron, which All the iron is supposed to be concentrated in 

increases with some regularity to the end of the the form of a perfectly smooth sphere, in 

perfemic series. The regularity is not sharp uniform contact with its envelope. The voland might better be described as a tendency, ume of the Earth, as generally accepted, is 

for the following reasons: 259,886,000,000 cubic miles. This corresponds 

In a single meteorite 9f large size the nickel- to a nuclear diam~ter of 6,284 miles and a 

iron is not uniformly distributed, and the radius of 3,142 miles. Subtracting this figure 

analyses were made on small fragments of not from the mean radius of the Earth, 3,959 

more than a few grams in weight. Adjacent miles, we get 817 miles as the average thickness 

fragments might have been either richer or of the ideal lithosphere. This, however, is 

poorer in nickel-iron than those which were only a first approximation to reality, and at 

least one correction to it is possible. analyzed. To analyze a complete stone is 

In calculating the average composition of the 

never practicable, nor is it feasible to sample a lithosphere one-third of it was assumed to be meteorite as one would sample an igneous rock 

or a carload of ore. These considerations equivalent to an average meteoric stone, but 

with one qualification. The disseminated 

amply account for the irregularities shown by nickel-iron, sulphides, and phosphides were 

the analyses. In spite ~f these difficulties the withdrawn from the stone and added to the 

tenden~y toward a definite _arrangem~nt of the nucleus, making it too large and the true 

meteontes seems to be faU:ly clear. !f. they lithosphere too small. The equality of volume 

really represent · a planetoid t~at . on~mally · as given between nucleus and envelope is 

resembled a small Earth, the distnbutwn of really that between the metallic (or rather 

a2 Farrington, o. c., Field Columbian Mus. Pub.I5I, mi. meteoric) iron and the silicate rocks. 

33372°-25--6 
78 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

The met31lic inclusions in the average 

meteoric stone amount to a little under 15 

per cent by weight, and even less by volume. 

An addition of 5 per cent to the volume of the 

lithosphere, and a corresponding ;reduction to 

the nucleus of the Earth, only lowers the 

diamete;r of the nucleus to 6,192 miles and 

;raises the thickness of the litho~phere to 863 

miles. This is probably a maximum correction, but any attempt at a greate;r refinement 

of the figures would be useless. Absolute 

accuracy is unattainable, for there is no sharp 

dividing line between the two components of 

the Earth. Furthermore, all the data which 

have been U:sed in the calcUlations, even those 

relative to the volume of the Earth and its 

density, are subject to corrections of undetermined magnitude and direction. There is, 

nevertheless, a strong probability that the 

diameter of the nucleus is of the order of 6,200 

miles and that the thickness of its envelope is 

less than 900 miles. Similar figures have been 

obtained by Wiechert,33 who assigns to the 

nucleus a diameter of 10,000 kilometers, or 

6,214 miles, to which a thickness of its envelope of 855 miles corresponds. Wiechert's 

results and mine were reached by entirely 

different methods, and their close agreement is 

therefore very satisfactory. Gutenberg,34 however, f;rom a study of earthquake waves, gives 

the nucleus of the Earth a radius of only 3,500 

kilometers, o;r 2,175 miles. The corresponding 

thickness of the lithosphere is 1, 784 miles, or 

double the value found in this investigation. 

It is for some geodesist to explain this discrepancy. 

Up to this point the vexed questions of 

pressures and temperatures within the Earth 

have not been considered. On the one hand 

it has been commonly assumed that because 

of increasing pressru·e the densities from the 

surface to the center of the Earth must have 

steadily increased, and a similar assumption 

has· been made with regard to temperatures. 

But here we have two opposing forces, one 

tending to increase, the other to diminish 

volumes. Whether these forces balance or 

not is a question which needs more consideration than I can give it. In its investigation 

many factors, hitherto generally neglected, 

have to be taken into account. The Earth 

33 Gesell. Wiss. Gottingen Nachr., 1897, p. 243. 

34 Gutenberg, B., idem, 1914, p. 176. 

is not a homogeneous body. It is .made up 

of many different substances, which are unlike 

in composition, in density, in fusibility, in 

specific heat, in conductivity, and in compressibility. Furthermore, we must determine 

whether compressibility is a limited property 

of matter or whether it can go on indefinitely. 

It is also necessary to consider the comparatively abrupt change from the envelope of 

silicate rocks to a nucleus of metallic iron, 

which seems to be sustained by strong evidence. 

The rocky shell of the Earth is more compressible than its metallic interior. Anything like 

a regular increase of density within .the Earth 

because of an assumed increase of . pressure is 

highly improbable. Unlimited compressibility 

would end in zero volume, which is absurd. 

There must be a limit somewhere, where 

pressure and the resistance to pressure exactly 

balance, and that limit may have been reached 

in the metallic ·nucleus of the Earth, an inference which is suggested by the rigidity of 

our planet. If it has not been reached then 

the volume of the Earth must be slowly shrinking, but of that· there are no clear indications. 

The assumption that temperatures within 

the Earth increase regularly with the depth 

is based upon a very short range of observations. In deep wells and other borings the 

temperature increases, but not to the same 

extent in all localities, the average amount 

being about 1° F. in 60 feet. The actual 

measurements are limited to depths of only a 

little more than a mile, and by extrapolation 

the conclusion has been reached that at the 

center of the Earth the temperature must be 

high enough to surpass the critical temperatures of all known substances. The temperature of the Sun, which is now well fixed as 

something like 6,000° C., would thus be exceeded manJ times over. Extrapolation sometimes leads to very surprising conclusions. 

Let us now consider the heat of the Earth 

under two distinct headings-namely, residual 

or original heat and new heat such as is constantly being generated. By residual heat is 

meant that which was retained by the cooling 

Earth within its interior, mainly in its nucleus 

and to a -less degree in the lithosphere. At 

and near the surface of the Earth the new 

heat becomes evident as the result of chemical 

activity, friction, and several other causes. 

. The heat derived from radium, as shown by 
I . 

/ THE EVOLUT!O.N A.ND DISINTEGRATION f F MATTER. 79 

the radioactivity of the rocks, has in recent but its thermal significance diminishes as it 

years received much consideration, but its recedes froml its focus, and below the isostatic 

importance may have been· exaggerated. It level, which is put at about 60 miles, it can not 

is, however, not negligible. That due to the be very great . At greater depths the temperaimpact of meteorites is relatively insignificant. ture, whatever it may be, is due to residual heat 

That chemical changes are constantly taking and is not higrher than the average melting point 

place in the crust of the Earth is a matter of of igneous rocks. . 

common observation, and each one has defi- The conditions in the nucleus of the Earth 

nite thermal significance. Some reactions are are very diff~rent from those in the lithosphere.· 

exothermic and others are endothermic, but Here we have a metallic mass more than 6,000 

whether these gains or losses of heat balance miles in dianleter, which is a good conductor of 

or one or the other predominates is difficult heat. It is practically insulated by a shell of 

and perhaps impossible to determine. Rocks poorly condulcting rock at least 800 miles thick. 

are decomposed by the joint action of air and Under · such I conditions, because of its conwater, and heat is both gained and lost in the ductivity, the temperature of the nucleus should 

rather complex processes. The intensity of be uniform or nearly so throughout and below 

the reactions is greatest, of course, in humid the :melting boint of iron, or 1,600° C. This 

areas and least in desert regions; it can not conclusion i~p ies that the nucleus has atbe the same for all localities. To discuss this tained a state of stable equilibrium, which is 

question at length would hardly ·be justifiable also indica ~ by the established fact that the 

in a paper of this kind: it is enough to show Earth as a whole is rigid. Only near the surthat the question deserves consideration. face is this rigidity disturbed. 

Even the heat emitted by volcanoes is in part, 

if only a small part, of chemical origin. The 

heat of some coal mines and of mines in which 

sulphide ores are worked is due to oxidation. 

Examples like these might be multiplied indefinitely. In many of the changes solar 

radiations also take part, and energy that may 

be released lateris stored up within the Earth. 

The crust of the Earth is constantly in 

motion, and every movement is accompanied 

by friction. The slightest tremor generates its 

share of heat, and its aggregate amount must 

be enormous. Mountains are raised to great 

elevations; rocky strata are folded, bent, 

broken, or distorted; there are landslides and 

all the varieties of erosion; and every one of 

these movements, great or small, is a source 

of what I have called new heat. Even volcanic heat is partly and perhaps largely due to 

friction. Volcanoes, as a rule, are situated 

along lines of weakness in the crust of the 

Earth, where earthquakes (and consequently 

friction) are most common. 

All or nearly all of this new heat is generated 

at or near the surface of the Earth. Below the 

level of isostatic compensation, the · depth at 

which surficial excesses and defects of density 

are balanced, there can hardly be much chemical activity and very littlefriction. An earthquake wave may penetrate to much greater 

depths, probably to the margin of the nucleus, 

NoTE.-Somelvaluable determinations of the compressibility of rocks ahd minerals have recently been published 

by L. H. Adams and E. D. Williamson (Franklin Inst. 

Jour., April, 1923). Their data, as applied to the present 

discussion, sht>w that the granitic rocks are the most compressible, and e denser rocks much less so. Granite is 

about three times as compressible as iron. From the surface of the earth to its nucleus, therefore, the compressibility dimini s, and the resistance to pressure must 

steadily increasr . 

THE · DISINI'EGRATION OF THE ELEMENTS. 

Our direct,l experimental knowledge of atomic 

disintegratioljl began with the discovery by 

Ramsay and I Soddy in 1903 of the emission of 

helium from radium. This discovery, however, 

was the outgrowth of two earlier discoveriesthat of radiof ctivity by Becquerel in 1896 and 

of polonium and radium by the Curies two 

years later. From these beginnings a new 

field of cher,ical and physical research has 

developed, 'f hich is already rich in fundamental discoveries and is represented by a 

voluminous l~terature. 

The study of radioactivity, however, covers 

only one phase of the main problem of elemental 

decay. As Joon as it was clearly recognized 

that the m9st complex elements were spontaneously depomposing, investigators began to 

attack the rroblem along other lines of research, some1 

of them experimental and others 

mathemati a~. The atoms that had been re-
\. 

80 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

garded as simple were seen to be complex, and 

it was sought to determine their structure. 

Attempts were and are still being made to 

decompose the chemical elements by artificial 

means, and some significant evidence of disintegration has been furnished by astronomy. 

The study of radioactivity is primarily, although not entirely, a study of the radiations 

which the most complex elements emit. These 

radiations are of three kinds, known as alpha, 

beta, and gamma rays, which differ in velocity 

and in the extent to which they can penetrate 

an obstacle in their paths, such as a sheet of 

aluminum foil. The · different products of 

radioactivity-that is, of atomic disintegration-are identified chiefly by the character of 

their radiations. 'rhe alpha rays are composed of helium atoms, the beta rays are 

"atoms" of negative electricity, and the gamma 

ray is regarded as possibly an electrically 

neutral doublet of two electrons of opposite 

sign. Through the study of these radiations 

more than thirty new substances have been 

discovered, which have received names and to 

which have been given atomic weights (except 

in the actinium series) and atomic numbers. 

In the following table, which is abridged from 

that recently published by the International 

Commission on the Chemical Elements, the 

present state of our knowledge of the radioactive elements is well shown. Some details, 

not needed in the present discussion, have been 

omitted from the complete table. The letter 

T at the head of the first column refers to the 

"period" of each substance-that is, the time 

in which the quantity of an "element" is 

diminished to one-half, the "half-life period," 

as it is commonly called. The column headed 

"radiation" gives the characteristic rays which 

the substances emit. 

This table evidently has no claim to finality. 

It is a valuable summary and classification of 

experimental data, but it also contains implications which sooner or later must be revised.· 

The basic facts are as follows: Uranium and 

thorium are ·slowly decaying, and in doing so 

they generate series of products which are also 

uns'table and which seem to end in the formation of lead. A few of these products are longlived, with periods measured by years; others 

change with almost incredible swiftness, and 

for some of them the periods consist only of 

minutes, or even of small fractions of a second. 

The disintegration of uranium and its products 

follows two distinct lines-one through ionium 

and radium, the other forming the actinium 

series. The thorium series, so far as we know, 

is single. 

Each of the three series given in the table 

divides at about its middle into two parts, 

with the line of demarcation marked by the 

appearance of the gaseous emanations of radium, actinium, · and thorium X. For these 

emanations the names "radon" (forme_rlyniton), 

"actinon," and "thoron" are proposed. These 

emanations are short-lived and give rise as they 

decay to what are called "active deposits,'' 

which are nonvolatile and can be collected and 

concentrated upon negatively charged metallic 

points or surfaces. These . deposits in turn 

decay, and so on to the end of the series. 

Now, without doubting the accuracy of the 

experimental data upon which the foregoing 

table is based, we may examine the inferences 

that are drawn from them. Here we must 

again point out the difference between normal 

and abnormal or defective elements. The 

normal elements are those which were developed in the ordinary course of evolution; the 

abnormal elements are those which were produced by decay. The difference between the 

two classes is very definite. The normal atoms 

are believed to be veritable storehouses of 

potential energy. In the series of radioactive 

elements that energy is becoming partly kinetic. The distinction is perfectly clear. Some 

of the products of radioactivity are too ephemeral to be called elements at all. They 

represent matter in a state of transition from 

one form to another, and the atomic weights · 

assigned to them are purely hypothetical. As 

for uranium and thorium, they are partly 

decayed and are still decaying, but they must 

have been originally developed as normal elements under conditions of pressure or temperature of which we know nothing. To quote an 

apt remark of Eddington/5 in his lecture upon 

the borderland between astronomy and geology: 

''In radioactivity we see a mechanism running · 

down which must at some time have been 

wound up." This fits the cases of uranium 

35 Eddington, A. S., Nature, Jan. 6, 1923. 
THE EVOLUTION AND DISINTEGRATION OF MATTER. 81 

The radioactive elements. 

The uranium-radium series. 

-

T. Name. Symbol. Atomic Atomic Isotope. I Radiation. weight. number. 

- I 

4.67X109 years Uranium I UI 238 92 u a 

24.6 days · Uranium X 1 uxl 234 90 Th {3 

1.15 minutes Uranium X 2 ux2 234 91 Pa {3 (-y) 

2X106 years Uranium II UII 234 92 u a 

6.9X104 years Ionium Io 230 90 Th a 

1690 years Radium Ra 226 88 Ra a (f3+'Y) 

3.85 days Radon Rn 222 86 Rn a 

3.0 minutes Radium A .RaA 218 84 Po a 

26.8 minutes Radium B RaB 214 82 Pb {3 (I') 

19.5 minutes Radium C - Rae 214 83 Bi 99.97% {3 and I' 

10-6 second Radium C' Rae' 214 84 Po a 

16.5 years RadiumD RaD 210 82 Pb ([3 and 'Y) 

5.0 days Radium E RaE 210 83 Bi {3 

136 days Radium F RaF 

(Polonium) (Po) 

210 84 Po a ( /') 

.......................................... Radium Q' RaO' 206 82 Pb .......................................... (Lead) Pb2os 

........................................... Radium C - Rae 214 83 Bi 0.03%a 

1.4 minutes Radium 011 Rae" 210 81 Tl {3 

................. ... ........... .................... Radium 011 Ra011 210 82 Pb ........................................ 

The actinium series. 

.......................................... Uranium? ......................... ? 92 u a 

1.04 days Uranium Y UY ? 90 Th {3 

1.2X 104 years Protoactinium Pa ? 91 Pa a 

20 years Actinium Ac ? 89 Ac -

19.5 days Radioactinium RdAc ? 90 Th • a ([3) 

11.4 days Actinium X AcX ? 88 Ra a 

3.9 seconds Actinon An ? 86 Rn a 

2.01Xl0-3 second Actinium A AcA ? 84 Po a 

36.1 minutes Actinium B AcB ? 82 Pb ([3 and 'Y) 

2.15 minutes Actinium C Ace ? 83 Bi a 

4.71 minutes Actinium C11 Ace" ? 81 Tl {3 and I' 

........................................ Actinium 011 Ac011 ? 82 Pb .......................................... (hypothetical) 

The thorium series. 

1.31Xl010 years Thorium Th 232 90 Th a 

6.7 years Mesothorium 1 MsTh1 228 88 Ra - 6.2 hours Mesothorium 2 MsTh2 228 89 · Ac {3 and I' 

2.02 years Radiothorium RdTh 228 90 Th a ([3) 

3.64 days Thorium X ThX 224 88 Ra a 

54 seconds Thoron Tn 220 86 Rn a 

0.14 second Thorium A ThA 216 84 Po a 

! 10.6 hours Thorium B ThB 212 82 Pb {3 and I' 

60 minutes Thorium C - The 212 83 Bi 65% {3 

10-n second Thorium C' The' 212 84 Po a 

.......................................... Thorium 01 Th 0 1 208 82 Pb .......................................... (Lead) Pb206 

.......................................... Thorium C - The 212 83 lli 35% a 3.1 minutes Thorium C11 ThC" 208 81 Tl {3 and I' 

.......................................... Thorium 011 Th a'; 208 82 Pb -- .............. -... - ..... -...... -.... ... (Lead) Pb2os 

.......................................... Potassium K 39. 1 19 K {3 

-----------------·-· Rubidium Rb 85. 5 37 Rb {3 

1 
82 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

and thorium exactly. When the conditions 

that permitted the evolution of uranium 

ended, then disintegration began. 

The atomic weights of normal uranium and 

thorium are unknown. 

The values assigned to them really represent 

mixtures of the normal elements with some of 

their decomposition products, of which we 

know only those that are revealed by their 

radiations. That. there may be residues left 

behind which are as yet undiscovered seems to 

be unquestionable. The actual determinations 

of atomic weight were made with masses of 

material containing millions of atoms, some of 

them intact and others represented by unexpelled products of disintegration. If all the 

atoms were broken down at once, there would 

be neither uranium nor thorium left. Furthermore, the atomic weight assigned to thorium is affected by another complication. It 

is doubtful whether any thorium compounds 

are known which are quite free from its isotope, 

ionium. The atomic weight of ionium has 

been shown by Honigschmid to be at least as 

low as 231.5, and probably lower. That of 

purified thorium must certainly be higher than 

the accepted 232.2, but the exact value is undetermined. The presence of ionium gives it 

too low a value. 

The atomic weights and numbers assigned to 

the products of radioactive decay are, with a 

few exceptions, hypothetical. The atomic 

weight of radium as actually determined is 

225.95, and it falls into place in the periodic 

system. For its emanation, radon, the value 

is near 222, but the determination is not as 

exact as js desirable. Radium, moreover, and 

also radon are still decayip.g, and the values 

given to them are therefore subject to the same 

uncertainties as those which affect the atomic 

weights assigned to uranium and thorium. If 

corresponding normal elements exist, their 

atomic weights should be somewhat higher. 

The so-called isotopes of lead will be considered later. 

From what has been said in the preceding 

paragraphs it is evident that the atomic 

weights and numbers assigned to .the radioactive "elements" are in need of careful reVIsiOn. The atomic weights start .from two 

that are certainly in error and are developed 

on the assumption that each step downward 

is due entirely due to the loss of alpha particles. 

But does that loss represent all the change ·I 

which has taken place? And how large a pro- · 

portion of the atoms in a given mass of uranium 

or thorium has been decomposed ? Furthermore, is Moseley's law of atomic nillnbers applicable to products of decay-for example, to 

radium C'? That product of radioactivity has 

a period of only 10-6 second; it comes into existence, pays a flying call on atomic number 84, 

and then vanisi1es. To call such a substance an 

element verges on absurdity. Moseley's law 

may be valid for the normal elements, but it 

has not yet been tested throughout the scale of 

atomic weights. The evidence in its favor is 

incomplete. In the actinium series no atomic 

weights are assumed, for the reason that the 

exact ancestry of actinium is still uncertain. 

None of these doubts, however, .attaches to 

the atomic weights of potassium and rubidium, 

two metals which are feebly radioactive but 

are independent of the uranium and thorium 

series. 

In the table of the radioactive elements six 

members are reported as isotopes of lead. 

That is, although the atomic weights assigned 

to them range from 206 to 214, they are given 

the same atomic number with lead, No~ 82, 

and appear in the same place in the periodic 

·classification. These isotopes are radium B, 

radium D, actinium B, thorium B, uranium 

lead, and thorium lead. Three of them are 

short-lived and need not be considered further 

here. Radium D, however, sometimes called 

"radio-lead," is part of the active deposit of 

radon; and it has been collected in sufficient. 

quantity for qualitative tests and gives some. 

reactions that are like those of normal or ordinary lead. Its period is 16.5 years, and its. 

hypothetical atomic weight is 210. 

The two isotopes that end the radioactive: 

series,' uranium lead and thorium lead, are on 

a different footing from the others. They are 

obtained from minerals containing them in 

sufficient quantities for good determinations. 

of atomic weight. These determinations give 

different values for the lead from different 

sources, showing that mixtures of normal lead 

with its isotopes are of common occurrence in 

radioactive minerals. In the most perfect and 

brilliant crystals of uraninite, which are found 

in granitic pegmatites, normal lead seems to be 
THE EVOLUTION AND DISINTEGRATION OF MATT'ER. 83 

absent, and the isotopic lead has an atomic 

weight very close to 206, the lowest value yet 

found. For thorium lead, derived from ores 

of thorium, the lowest value is 208. Are 

these the real ends of the radioactive series, 

or does disintegration proceed still further~ 

So far, this question is not completely answered. 

The existence of these isotopes has led to a 

belief, or rather a suspicion, that ordinary 

lead is a mixture and not a single definite 

substance. How far is this suspicion verified ? 

Is the atomic weight of ordinary lead constant 

or variable? To answer these questions Baxter 

and Grover made elaborate series of analyses 

of lead bromide and chloride from very different sources. Lead was obtained from galena, 

cerusite, vanadinite, and wulfenite, and the 

minerals came from widely separated localities-namely, Idaho, Arizona, Washington, 

Missouri, Germany, and Australia. Four different minerals and seven localities furnished 

the material for the determinations, and commercial lead nitrate was also included in the 

investigation. Four series of determinations 

were made, giving average values for the 

atomic weight of lead ranging from 207.18 to 

207.23, an extreme difference of 1 part in 

4,144, which is quite within the allowable 

limits of experimental uncertainty. The 

atomic weight of normal lead is a definite 

quantity and not a statistical average of the 

different values found for its isotopes. To 

maintain such a uniform average the isotopes 

should always· be mixed in exactly the same 

proportions, and that.is extremely improbable. 

One very uncertain assumption has been 

made as to the nature of isotopes. Those of 

lead, for instance, are said to be cheinically 

identical and not separable . by chemical 

methods. That simply means that no such 

separation has yet been effected;· but there is 

no proof that it may not be effected in the 

future. The prediction of impossibilities is 

not always verified. Many failures are on 

record. 

That the products of radioactivity are products of decomposition is proved, but their definiteness is not so certain. All or nearly all of 

them are unstable and undergoing change, some 

rapidly and others with extreme slowness. 

Their· isotopy, moreover, is largely hypothetical, for how can two products be called isotopic 

when both are undergoing alteration and at 

different r ates? Only for uranium lead and 

thorium lead can isotopy be regarded as established; and even for these the claim must be 

held with reservations. The isotopes differ 

from normal lead in some physical properties, 

but that they are its equal as regards stability 

is still uncertain. The stable product of evolution and the products of decomposition are not 

quite the same. Their similarity may be illusive. This possibility should not be ignored. 

Reference has already been made to Aston's 

work on " mass spectra" -work which is of 

great value, regardless· of any interpretation 

that may be put upon it. Are his isotopes 

substances of the same order as those that 

appear in radioactivity? 

The "mass spectra" described by Aston 36 

represent an artificial disintegration of elements, and his process is roughly as follows: 

An element or one of its compounds is bombarded by powerful positive rays in a magnetic 

field. The rays, differently deflected, finally 

impinge upon a carefully calibrated photographic plate, upon . which they give lines that 

are interpreted as belonging to isotopes. From 

the position of these lines the atomic weights 

of the isotopes are determined within a supposed accuracy of 1 part in 1,000, or one-tenth 

of 1 per cent, a rather large uncertainty. 

It is not necessary for present purposes to go 

into the details of Aston's work. They are 

fully given in his book on isotopes. Suffice it 

to say that his apparatus, his "mass spectograph," is very complicated, and his technique 

is exceedingly refined. The essential fact is 

that the elements undergo certain changes 

when subjected to the action of positive rays. 

Other methods for attaining results similar to 

Aston's have been developed by Sir J. J. 

Thomson and by A. J. Dempster, but they also 

are . applications of what is called positive-ray 

analysis. The products of these analyses, regarded as isotopic, are given in the following 

table, which is abridged from the table published by the International Commission on the 

Chemical Elements in 1923. The figure relating to glucinum is due to G. P. Thomson; 

those of magnesium, calcium, and zinc, to 

Dempster; all the others are Aston's. Anumber inclosed in parentheses is doubtful. 

a6 Aston, F. \V ., Isotopes, London, 1922. 
84 

~ Atomic ~ Atomic num- CD weight. s her. CD 

~ --

H 1 1. 008 

He 2 4.00 

Li 3 6.94 

Gl 4 9.02 

B 5 10.9 

c 6 12.005 

N 7 14.008 

0 8 16.000 

F 9 19.0 

Ne 10 20.2 

Na 11 23. ·oo M()' 12 24.32 

AI 13 27.0 

Si 14 28. 1 

p 15 31.04 

s 16 32.06 

Cl 17 35.46 

A 18 39.9 

K 19 39. 10 

Ca 20 40.07 

Fe 26 55. 84 

Ni 28 58. 68 

Zn 30 65.37 

As 33 74.96 

Se 34 79.2 

Br 35 79.92 

Kr 36 82.92 

Rb 37 85.45 

Sn 50 118.7 

I 53 126.92 

Xe 54 130.2 

Cs 55 132.81 

Hg 80 200.6 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923. 

Isotopes. as the atomic weights become larger. This 

Minimum 

number 

of isotopes. 

1 

1 

2 

1 

2 

1 

1 

1 

1 

2 

1 

3 

1 

2 

1 

1 

2 

2. 

2 

(2) 

(1) 

2 

4 

1 

6 

2 

6 

2 

7 (8) 

1 

7 (9) 

1 

(6) 

Masses of isotopes. 

1. 008 

4 

7;6 

9 

11; 10 

12 

14 

16 

19 

20; 22 

23 

24; 25; 26 

27 

28; 29; (30) 

31 

32 

35;37 

40; 36 

39; 41 

40; (44) 

56; (54)? 

58; 60 

64; 66; 68; 70 

75 

80;78;76;82;77;74 

79; 81 

84;86;82;83;80; 78 

85;87 

120; 118; 116; 124 

119; 117; 122; (121) 

127 

129;132;131;134; 136; 

128; 130; (126); (124) 

133 

(197-200); 202; 204 

increase, however, represents only a distinct 

tendency, not a definite law. How far th"s 

rule may hold remains to be determined; and 

it is extremely desirable that the mass spectra 

of the elements above mercury in the seale of 

atomic weights should be examined-namely, 

those of thallium, lead, bismuth, thorium, and 

uranium. Such an examination would render 

a direct comparison with the radioactive series 

possible. Would the mass spectrum of lead, 

for example, show the same isotopes as those 

which have been · revealed by radioactivity? 

That of uranium, also, should be very instructive. The most complex elements are the 

most easily decomposable and should show 

the greatest number and variety of fractions. 

So far the evidence favors the hypothesis of 

decomposition; but there is also evidence to 

support the isotopic theory. By diffusion or 

by distillation three elements-namely, chlorine, zinc, and mercury--have been separated 

into fractions that differed in density and in 

atomic weight. Harkins and his colleagues,37 

by fractional diffusion of gaseous hydrochloric 

acid, have partially separated it into two 

portions, one heavier and the other lighter 

than the ordinary compound. The heavier 

portion gave an atomic weight for chlorine of 

35.4918, which is 0.1 per cent higher than the 

accepted value, 35.46. The latter value has 

been determined with the greatest accuracy What do the figures in the last two columns and is probably correct within 1 part in 10,000. 

of the foregoing table really mean? Do they Results similar to those of Harkins and Hayes, 

represent isotopes in the accepted meaning of but by a different method, have been obtained 

the term, which are merely separated by the by Bronsted and Hevesy,ss who separated 

bombardment? · Or are they a record of an hydrochloric acid into two fractions correelemental disintegration? These alternative sponding to a difference of 0.024 in the atomic 

interpretations are both tenable, and each one weight of chlorine. The chlorine atom, then, 

can be sustained by cogent arguments. The seems to be a doublet; but the remarkable 

second question is answered by Aston in the uniformity of its chemically determined atomic 

affirmative; and his views have been generally weight is difficult to explain. A mere mixture 

accepted or at least favored. On the ·other of two isotopes could hardly be so definite 

hand, the isotopes of the radioactive series are unless all the compounds of chlorine that were 

definitely products of decomposition, and those used in the determination of its atomic weight 

of the mass spectra may be of the same order. had a common origin. That possibility is still 

The last column of the table is extremely under investigation. Is the chlorine of volsuggestive. The simplest elements, those of canic emanations, of meteoric iron, of oceanic 

low atomic weight, show little or no isotopy. salts, and of igneous rocks always the same 

Twelve of them are simple substances an~ may thing, and of one definite atomic weight? 

be called pure or normal elements. N 1ne of By fractional distillation mercury has been 

them, up to and including nickel, are doubled, separated into ·two portions, one heavier than 

and two are represented as triplets. With · · t · d f 1 · t I 37 See especially Harkins, W. D., and Hayes, A., Am. Chern. Soc., z1nc a grea er egree o comp ex1 y ~ppears, Jour., vol. 43, p. 1403, 1921. 

Which, with SOme exceptions, tends to Increase as Bronsted, J. N., and .Hevesy, G., Nature, vol. 107, p. 619, 1921. 
THE EVOLUTION . AND DISINTEGRATION OF MATT'ER. 85 

the other, as in the case of chlorine. Harkins 

and Jvfadorsky 39 evaporated mercury in a 

vacuum and obtained two fractions that gave 

differences from the accepted atomic weight 

of the metal of + 0.052 and - 0.044. Bronsted 

and Hevesy/0 by a similar process, obtained 

results of the same order. The same cheinists, 

however, in a later investigation, 41 determined 

the density of ordinary mercury from ten 

widely separated sources and mnd differences 

of only 2 to 6 units in 10 millions. These 

differences in density correspond to differences 

in atomic weight of 0.0004 to 0.0012. 

By very thorough determinations of atomic 

weight Honigschmid and Birckenbach 42 have 

completed the evidence as to the composite 

nature of mercury. Bronsted and Hevesy 

supplied them with samples of their heavy 

and light fractions, with which the deterrninations were made-for the heavier fraction, 

Hg=200.628 to 200.638; for the lighter fraction, Hg = 200.562 to 200.568. These differences are conclusive. For ordinary mercury 

the same chemists, aided by M. Steinheil, 43 

found Hg= 200.61, the accepted value. 

Ordinary or normal mercury, if we may call 

it so, is therefore uniform in character far 

within the limits of experimental uncertainty. 

The same is true of lead, as we have already 

seen; and the work of Baxter and his cola borers 

have shown it to be true of iron and nickel. 

The atomic weights of terrestrial iron and 

nickel are identical with those of the two 

meteoritic metals. In order to account for 

this uniformity we must assume in each case 

that the component isotopes must always have 

been mixed in constant and definite proportions. 

For the possible complexity of zinc there is 

only the work of Egerton,44 who in a preliminary note reports finding small differences 

in the density of the metal after distillation 

in a high vacuum. Two fractions gave densities of 0. 9971 and 1.00076, when that of the 

initial substance was taken as unity. These 

results are regarded as promising. 

So far a partial separation of chlorine and 

mercury into distinct fractions has been accom39 Harkins, \V. D., and Madorsky, S. L., Am. Chern. Soc. Jour., vol. 

45, p. 591, 1922. 

40Bf6nsted, J. N., and Hevesy, G., Nature, vol. lOG, p . 145, 1921. 

41 Zeitscbr. anorg. nllgem. Cbemie, vol. 124, p. 22, 1922. 

42 Honigscbmid, 0., and Birckenbacb,L., Deutsch. cbem. Gesell. 

Ber., vol. 56, p. 1219, 1923. 

43 Idem, p . 1212. 

44 Egerton, A. C., Nature, vol. llO, p. 773, 1922. 

plished, although the differences bQtween the 

fractions are very sma1l. A complete separation is yet to be effected, so that each fraction 

can be weighed and examined by itself. If 

the mass spectra really represent isotopes 

there should be twelve possible isotopes of 

mercuric chloride, ranging in molecular weight 

from 232 to 241, a difference of 9.unitsin atomic 

mass. The fractional crystallization of mercuric chloride, then, or else precipitation of 

the mercury either by electrolysis or with some 

suitable reagent, might yield definite results. 

Other lines of attack upon the problem of 

separation have been suggested, and they are 

summarized by Aston in his book. Greater 

detail is not needed here. 

Evidence of an entirely different character 

as to disintegration of elements has recently 

been obtained by Rutherford. 45 'His procedure, briefly, is as follows: A stream of powerful alpha rays, emitted from a very thin film 

of radium C, is passed through a current of · 

hydrogen. A number of high-speed hydrogen 

atoms are liberated, which strike upon a screen 

of zinc sulphide and produce scintillations that 

can be observed through a microscope and 

counted. Between the zinc sulphide and the 

radioactive source thin screens of mica are 

inserted, which can be varied in thickness, 

so as to measure the relative penetrating power 

of the alpha particles and of the hydrogen 

atoms. The range of the hydrogen atoms is 

much greater than that of the alpha rays and 

so gives a datum for their identification. Their 

appearance, as found by the scintillations on 

the zinc sulphide, identifies them as hydrogen. 

Suppose, now, that some other gas replaces 

hydrogen. With nitrogen the same longrange particles appear, this giving evidence 

that the lighter element is a constituent of 

the nuclei of the heavier atoms and has been 

separated from them. With oxygen or carbon 

dioxide no such change is observed, a very 

significant difference. The moh~cular weights 

of these gases are whole multiples of that of 

helium, from which carbon and oxygen are 

supposed to have been built up. 

By this general method, with modifications 

in the case of solid substances, Rutherford 

has tested all the elements up to atomic weight 

40, with the exception of helium, neon, and 

argon. Several other elements, higher in the 

40 Rutherford, Sir Ernest, Nature, vol. 109, pp. 584--586, 61-1-617, 1922. 
86 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY,' 1923. 

scale, were also tested, but none above phos- nebular type has been repeatedly observed 

phorus gave positive results. Boron, nitro- and recorded upon photographic plates. 46 

gen, fluorine, sodium, aluminum, and phos- The close relation between planetary nebulae 

phorus yielded long-range particles, from and Wolf-Rayet stars has been emphasized by 

which it is concluded that hydrogen atoms are · Adams and Pease and also by Wright. Adams 

contained in their atomic nuclei. Elements and Pease even go so far .as to suggest that 

with atomic weights that are whole multiples some of these peculiar stars were probably at· 

of 4 give no hydrogen particles when bom- some former time novae from which the nebubarded with alpha rays. The hydrogen-helium lar gases have .disappeared. This Is not at al1 

theory of the constitution of the elements improbable, fO!' the spectra of the Wolfthus receives some support. Will it hold good Rayet stars are found to contain many lines 

for the more complex elements~ That re- of no known origin. Do they represent decommains to be seen. Not until an element has position products, the end results of atomic 

been completely disintegrated into identifiable disintegration~ The novae at the summit of 

hydrogen and helium can the question be their careers have enormously high temperadefinitely answered. So far only a few atoms tures, at which few of our familiar elements 

among millions have given evidence of atomic could exist. The conclusion is almost inevitdisintegration, and we can only guess at what able that the process of elemental evolution 

remains after the hydrogen particles have has been reversed, but if that is true, what are 

been expelled. However, a promising attempt th.ese decomposition products, and how can 

has been made toward the artificial breaking they be included in the scale of atomic num-

.down of atomic nuclei, but it is only a begin- hers~ To this question no answer can yet be 

ning. It would be unfair to expect much given. The evidence of disintegration, howmore in so young a field of research. ever, seems to be very strong. 

That the evolution of a star is accompanied To what cause, now, can we attribute the 

by an evolution of the chemical elements phenomena of the novae~ On this subject 

seems to be established, at least to a high there are two principal hypotheses. One asdegree of probability. But is the process ever sumes a collision between two stars, two huge 

reversed~ This question can be answered masses, moving with great velocity and so genin the affirmative. Every now and then an erating the heat that is revealed by the brilinsignificant star, visible only through a liancy of the new star. This hypothesis, howtelescope, suddenly flashes into great bril- ever plausible _it may be, is not now generally 

liancy, sometimes even rivaling Sirius in held and needs no further consideration here. 

brightness. This condition lasts for a short The probability of such collisions is very slight. 

time, and then the "new star" gradually The other hypothesis, which seems to be 

fades away and returns to something like its more probable, assumes that a single star 

former insignificance. $o much is shown by passes through a dark nebula, or else through 

the telescope alone, but when the spectro- a cloud of meteoric dust, with retardation of 

scope is also used much more is revealed. The motion attendant friction, and therefore a 

spectrum and therefore the composition of the great development of heat. The same thing 

star has changed, a~d a ~omplex system has happens, but on a much smaller scale, when a 

reverted. to somet~Ing simpler . . _When the meteorite enters the atmosphere of the Earth. 

reversal Is co~plete Its end product Is a planet- The difference is merely one of degree. In the 

ary nebula With a Wolf-Rayet star as a nu- larger body the heat is sufficient to disintegrate 

cleus. In some cases the reversal does not go th 1 t · th ·11 · 't nl lt . e e em en s; In e sma er I o y me s a 

so far, and these exceptiOns are probably due thin :til th f f th f ll' . . . . m on e sur ace o e a Ing mass 

to differences In the vwlence of the outburst hi h · b k · t f t · w c Is ro en up In o ragmen s. that was revealed by the sudden ·appearance · 

of the supposedly new star. The term new, 46For examples see Cannon, Annie J., Harvard Coil. Observatory 

h · h dl · t h t h Annals,vol.S1,No.3,1920; Adams,W.S.,andPease,F.G.,Nat.Acad. OWever, IS ar Y appropr1a e: W a as Proc., val. 1, p. 391, 1915, and Astrophys. Jour., vol. 40, p. 294, 1914; 

really happened was the almost instantaneous Wright,W.H.,idem,p.466. NovaGeminorumNo.2andNovaAquilae 

transformation of a dwarf star into a giant. No.3 are two of the most typical instances of the reversal of a star to a primitive type. I am indebted to Professor Harlow Shapley for Miss 

In recent years the complete reversion to the cannon's paper on Nova Aquilae.