The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1836-12-02 00:00:00

THE LIVERPOOL STANDARD.

POPULAR
.COURSE. ON
_,CHEMISTRY, AT TH E

MECHANICS' INSTITUTION:

LECTURE IV.
On Saturday Mr. "lemming proceeded with his instructive
and entertaining lectures.
We have to consider in the present lecture the application of
chemical affinity to that very importaut branch of our manu-
factures, the manufacture of pigments and dying materials.
"There are perhaps very few branches of manufacture known, to
which chemical discoveries have been more useful than to this;
for we are now possessed of ►',any valuable pigments of greater
durability and beauty than any known in former times. the
',lost of whieb are made from substances formerly considered
useless and worthless, all to be obtained with very little cost
and trouble. and all manufactured by very simple processes.
The first of these is the well-known pigment Prussian blue. It
is so called because it was first discovered by accident at Berlin
by Diesbach as he was forming a precipitate by the agency of
cochineal, a solution of sulphate of iron, and an alkali. The
alkali which he used for that purpose was obtained from a che-
mist, who manufactured it by a peculiar process, in which he
used animal blood. Upon appisiing this alkali, he was sur-
prised to find. instead of a crimson .precipitate, one of a deep
blue colour. He obtained inure of the alkali, and added it to

carbonate of lead and acetate of lead simultaneously formed.
The vinegar undergoes decompoSitien, and in the course of a
few weeks we have a crust (Attie carbonate of lead formed upon
the metallic lead, but it will take three months to convert the
whole sheet of the ordinary thickness into white lead. When
a thick film is firmed upou the lead it is removed, in order to
expose a fresh surface of metal to the action of the vinegar. The
operation of removing this crust was formerly destructive to
health, inasmuch as the workmen were generally afflicted with
what is called the painter's cholic, which caused them contrac-
tions of the thumb, the elbows, and knees. This arose from the
unsciemitic manner in which they removed the carbonate of
lead. ln removing the lead it is said that one of in twenty was
broken, besides which the lead was brushed off, by both or which
circumstances it is obvious that a number of fine particles of
lead would mingle with the atmosphere and enter the lungs of
the workmen. A simple plan is now adopted by which this
complaint is prevcuted,—it is merely the removal of the crust
of lead under water.

VerditeTi; another of the pigrrtents produced by chemical
aality. It is both blue and green. The green is made of the
waste nitrate of copper, which the Sheffield manufacturers have
left in the process of recovering silver nom waste cuttings at
pitted copper. By adding lime to this nitrate a green colour is
produced, which may be changed to blue by the addition of an
alkali.

solutions of cochineal and sulphate of iron, and found that it
affected the latter only. .11e continued to precipitate the coin-I • LucTune V.
nouud, and sold it at an immense: price under the name of On Wedneedey evening Mr. 1-lemming introduced and ex-
Prussian blue. The alkali be used was ferro crintiret of po- plained the various modes of producing artificial light,prepara-
tassiton. The pigment-is fermeil4ty adding a solution of fern) tory to which he expounded the general properties of natural
cyanuret of pnteesiutie to a solution of sulphate of iron, wheu light. The attendance was more numerous than at any previous
the sulphuric acid unites with the potash, and the cyanogen to lecture.
the iron. In the manufacture of Prussian-blue it is most itimlis- We have now to consider the different modes of obtaining and
pensable to have peroxide of iron, otherwise the precipitate will supplying artificial light. As the physical properties of light
be green. The sulphate of iron of commerce contains both pro- produced artificially and naturally are similar, it might be as
Oxide and peroxide of iron. ir protoxide of iron is exposed to well, in the first place. to say a few words respecting them. The
the atmosphere, it combities with the oxygen of the atmosphere, first question that will naturally arise is, " What is light ra Is
and becomes a peroxide. In the manufactured Prussian blue, it a material substance, or is it a property of matter, or is it
the manufacturer, after haviug precipitated the pigment us pre- something as distinct from m itter as sounds from the ody pro-
vioustv described, adds a large quantity of the solution of alum; clueing them ? There have been two theories propounded on
indeed the solution of alum is generally mixed with the solution this subject, both of which bave been ably supported. The first
of sulphate of iron. When the solution has subsided, it is filtered of these, called the copuscular theory, which was advocated by
and washed with muriatic acid. Both of these latter processes are Newton and others, is losing ground ; whilst the undulatory
unnecessary. 'The addition of alum is professedly twitle to give theory, supported by Euler and a number of eminent philoso-
the pigment what they call body; hurt the idea is absurd, the Idlers. is dilly superseding it. According to Newton, and the
blue is as well without it. It is in reality only added to increase corpuscular theory, light is matter thrown from the sun in minute
the profit of the manufacturer; the blue is worth a great deal, particlesacalled rays, each of which proceeds in a rectilinear
whereas the alien is coMparatively worthless. When persons direction, and that the substances on which these particles iin-
are purchasing Prussian blue, they put their tongue to it; and it' pinhe become luminous by repelling them. if this be correct
it adheres forcibly to the tongue, they sac it is good; but, as this' it is difficult to obtain an idea of the nature of •a ray of light.
adhesion Irises troin the alum cootainedin the pigment, them can- because it is a law in mechanics that the momentum with which
trery is the case. Tile vreshing with mimetic acid is to dissolve a body will impinge, upon another depends upon its size and
the protoxide; but if the precipitate were to remain exposed to velocity. Thus, for examrle, a cannon-ball is a moreadestruc-
the atmosphere for a short time, the same effect would be gained. tive weapon than the battering ram of ancieut•wartare, merely
Thit pigment manufacturer is compelled by necessity to adul. because its velocity is greater. If we suppose a battering rain
termite his compounds, as the competition is so great that he to weigh 1000 pounds, and to swing to and fro with the velocity
cannot afford to sell tile genuine article. There is whither of ten feet in a second of time, the weight multiplied into the
agent by which we can at once manufacture Prussian blue, velocity will give an idea of its force. lint if a cannon-ball,
which is also a very valuable test for the detection of iron. It only weighine ten pounds, move with a velocity of 1000 feet in
is still the fern, cvenuret of potassium; but a solution of chin_ a second the same effect will-be produced—the force will be the
rine gee is passed through it, which communicates to it a blood same. That a superior momentum is created by superior velo-
red colour. This solution is then boiled to expel the' free chip- city is a fact well known to most persons. If we throw a muss
rine. 'lie chlorine takes away half an atom of potassium from ket-bell against a hoard, we shall merely make a slight indenta-
the compontel. 'This test will not detect peroxide, but only tion upon it; but if the saute bell be discharged from the mouth
protoxide of iron ; and of such delicacy is it, th it the presence of a musket it will make a hole through the board. It must be
of a few drops of protoxide of iron in a gallon of water will be evident that the ball, in either instance, will weigh the same,
perceptibl r indicated. This test is constant y employed in and therefore that its greater force is simply occasioned' by its
London by those benevolent iarlividuals the officers of Excise, being impelled with a greater velocity. Whether the human
who ge about doing good, in detecting the aduterations of the arm be moved quickly or slowly its weight is the same, but not
London riblicans, s tine of whom are constantly in the habit of its force. Accordingly in pugilism it is well known that the
making three butts of porter out of two by adding copperaa, force of the blow is in proputtiou to the velocity with which the
salt, and. burnt sugar to their beer. The officers cairy with mm strikes. Thus a small, a tie tk, or a light matt Will produce
them the test alluded to, and when they detect the presence or a greater effect with a quick menial than a powerful man with
the sulphite of iron its the porter, they itinnediately submit it a slow motion. Now, according to, Newton, light is composed
to Dr. Faraday, who is analytical chemist to the crown, and the of small particles of rays of light, amid these particles move at
offender is instantly lined. With respect to the very beautiful the rate of 200 J miles in a second of time; therefore, as mo-
smit whihh is the material used in the manufacture of Prussian menthe' is equal to the velocity, multiplied by the weight, and
bate, it is made by a Very singular and easy price:4 out of Writ- as•this' velocity is infinitely greater than that of any body ex-
terials of very little value. It is manufactured by heating in istittg upon flits earth, the weight of the particle or ray must be
an open iron vessel dried animal blood with a sufficient quan- , inconceivably minute. Let us suppose, for the sake of example,
tits of pearl ash. During the procesi of fusion, it must be dill- the velocity to • be, in round numbers, two iniilions of times
gently stirred with an iron spatula. If we attempt to make this greater than a cannon-bell. If, then, the velocity of light be
emenonutid in a vessel which is not iron, we must add a portion this, it follows as a natural consequence that, if a ray of light
or iron fiangs to it. When the mass has become pretty well were as large as the two millionth peat of a grain of sand, it
incorporated in a p isty form, and the animal matter has been would produce as great an effect as that of a grain of sand forced
well burned off, the remainder is set aside to cool, and when from
_a cannon mouth. We have, however, in better reason for
, cool, water is introduced, by which all that is soluble is disiolved supposing that light is a material body than that sound is a ma-
tted drawn off. 'Phis liquid will be found to contain the salt, terial body. If a glass be struck with a finger a distinct sound
which may be crystallized in the ordinarY manner. Sometimes will be heard, but we are not to suppose that when the glass is
bouts or horns in a state of mechanical division are employed struck that any particles of it are detached in the operation and
instead of blited. It does not appear, however, that cyanogen hill upon the tympanum of the ear. It would be absurli
is contained in either of these substances already formed, but to suppose that this is the case, and yet we have no better
that they content the element.; carbon tin& nitrogen, which are reason fur supposing that light is produced by small par-
required for its existence. Sulphate of iron is niade artificially titles of matter impinging upon the eye. According to the
from iron pyrites, which are exposed for two or three .ears to undulatory theory we are told that light is produced like sound,
the action of the atmosphere add rain, front which ithiasorbs that the whole of the universe is filled ' with' a certain bighle-
the requisite degree of Oxygen, and, being dissolved by the rain, attenuated and subtile fluid called ether, which is not light of
is carried into pith constructed to recelve it. This solution is itself, but. produces light when thrown into vibration by the
evaporated and crystallized into the well-known salt sulphate of peculiar 'action of a luminous body. In short, that this ether is,
iron or copperas. with
.respect to light, what 'our atmosphere is with respect to
'We havewow to consider the chrome colours. These also sound-elf neither of theta existed then there would be neither
hites superseded all similar colours previously used, being More light nor sound. The air is throwri into a series of undulations
durable and cheap. They were not discovered, like Prussian by the voice, and' produces sensations of seuud. These
blue, by accident, but by scientific investigations, about forty undulatiuns. are slather to those palpable and visible waves pro-
hears ago. At that period a French chemist, Vanquelin, was (Meet! by throwing a pebble into water,-which proceed from the
analyzing the red lead ore of Siberia, the nature of which was pebble as froma centre antil they reach the verge of the water.
Until then unknown, although it had been for a long time used We wey,suppose that light is produced in a similar manner,
sea pigment in Siberia and the northern parts of Russia, where exceptingthat its waves proceed in every direction, not inertly
it existed formerly iu abundance. In analyzing this substance horizontally, but laterally, vertically, acid in everypossible di
the French chemist found that the lead was combined with an, rection. According to ihlewton'S theory the different colours
acid which, front is properties of separatiug various compounds, constituting a ray of light are seven, or at least. three, out of
he called chromic acid. The substance in question was chro- which the remaiuder may be produced,' and that these colours
mate of lead. The quantity of chrome obtained from this ore are caused by a difference of size in the particles. According
-is small; but shortly after it was discovered that an atnnidance to the nudulatory theory the difference of colours proceeds from
of the ore might he procured in France, where the oxide of the different velLcities of the waves of light, some of- them tra-
chromium existed in combination with oxide of iron. The ox- Telling swifter than others. if it be difficult to conceive what
ide of chromiuM is converted into chromic acid in the process may be the size of particles of light, it is equally difficult to con-
of manufacture. Shortly afterwards it was discovered that ceive how infinite these undulations must be, or how rapid they
mountains of it existed in the Shetland Island's, and it was ime may be, amounting as they do to billions of waves in a second
of time. Newton was the first to effect the decomposition of a
pouted from thence for the purpose of forming this pigment.
The very beautiful pigineut called chromate of lead Is formed ray of light into seven different colours. lie received it through
les adding a solution of biebrumate of potash to a solution of
a hole iu a window shutter, and refracted it through a triangh-
acetate or nitrate of lead; and when this pigment was intro-
lar prism. These seven rays were again attempted to be de-
duced into Great Britain its price was two guineas a pound—the composed, but were found incapable of further decomposition.
' lecturer himself remembered, 15 to 1G years ago, having given It is supposed that these seven primary rays are composed of
m half-a-guinea fora pound of it. The secret of its manufacture three rays—red, yellow, and blue. It is therefore by the bar-
: soon became known, and its price consequently gradually de- moneous blending of these three rays that the seven different
dined: it can now be had for 2s. 6d. per lb., or as much less as tints are produced. When these are not decomposed they at-
you. please to give to have it properly adulterated.. George IV. ford a white light. Black is an absorption of light, or a cepa-
, was the earliest patrouizer of this pigment, and attracted touch city for absorbing a portion, and a body always appears of that
attention to it. Struck with its beauty, he caused an apartment colour which it. is most averse to, or of that colour which it re-
in Carlton Palace to be painted with it. . This drew the oaten- fleets. 'ln reality there is no substance which we can see by
tion of the nobility to it, and it was bought up fur the purpose any light which will be exactly either black or white. There is
of painting carriages. Patent yellow was previously employed not any substance capable of reflecting or absorbing all the co-
for this purpose, but where a brighter or livelier colour was re- lours. This may be proved by experiment. Thus a coat which
quired, what is called King's yellow, sometimes Queen's yellow, appears black in ordinary light will appear white if a much
was employed. Soon alter the process of manufacturing the greater quantity of light be thrown upon it. A burning glass
bichromate of lead became knoWn the pigment was reduced in will effect this by concentrating the light upon a pat ticular por-
price. The first process in making this salt is to reduce the ore tion of the coat. In like manner if we direct the focal rays of a
to the state of powder, and then mix it with common saltpetre;
nsistakeu in supposing it previously to be white. Light is . re-
similar glass upon white paper, we shall find we were very much
it is then heated to redness iu a crucible, when a decomposition
,
of the nitrate of potass and the chromate of iron takes place. fracted as it passes through different mediums. We must suppose
One portion of oxygen combines with the chromium, and cue.' that light passes in a rectilinear direction from the sun to the
vents it into chromic acid, which will combine with the potass, confines of our atmosphere, but that it will there be bent out of
forming bichromate of potass. Water is then added to the that course in consequence of the medium beerneing denser,
mixture, when the bichrumate of potass being dissolved is re- and that it will become more refracted for this reason as it ap-
moved, a further quantity of saltpetre is then added to the re- broaches the earth. The earth is besides constantly moving.
maimidet, and heated, to extract the remaining portion of chro- on account of these two circumstances we never see the sun or
!Muni which the iron may contain. Chrothium is a very durable any celestial body in the true position. A ray. of light occupies
colouring matter, and forms the colouring matter of some of our eight minutes and thirty-two seconds in its passage from the sun
Garest gems. The'sultition of bichromate of potass in water is to our earth. It was formerly supposed that the phenomena of
the Most powerful colouring matter we possess, for one part of light was instantaneous, that the instatait was transmitted from
it will colour 240,000 parts of water. In London the lecturer 'the sun, that instant it passed to the earth. The error was dis-
hed recoutinended the solutiou to the druggists fur their show covered by observing the different periods of time in which Ju-
. bottles, because it does not undergo decomposition, and may he piter's satellites emerged from his shade, according to the vu-
varied in tiut. By adding a solution of bichromate of potass to nous places of the earth in her orbit. By this means we find
and
the time that light takes in travelling from the-sun to the earth.
a solution of acetate of lead, we shall immediately form the
beautiful pigment bichrotnate of lead, is hich will fall down in
a beautiful yellow precipitate. The manufacturers adulterate Owing to the refraction of light we see the sun eight minutes
thirty-two seconds before we otherwise' should be able when
this ni it rises, and for the same space of time after it has actually set.
We iiiiatulcnt to a considerable extent to increase their profits.
~ may increase the iuteusity and beauty of this pigment by
heating it whilst in a state of solution with a small quantity of Thus,
t 51r. [lemming beautifully illustrated by sticking a num-
alkali, when it assumes a deep orange colour. We have uther her of waters at different heights in a bowl, amid desiring the
chrome colours formed of metals which are of great beauty. spectators to count the number they could perceive ; he then
The chronhe green, filled the bowl with water, when a much greater number of wa•
which has superseded almost every other, is fers could be distinguished, owiuu' to the different refractive
exceedingly. beautiful and durable and is made by mixing to- powers of the air and water. Mr. 'lemming then explained the
gutter a A"lutiott of sulphate of copper with a solution of the causes of the rainbow; for the discovery of the theory of which
bichrontate of petite., but it requires to be precipitated by an
,'Phis' green is likewise adulterated by the ma- he said we were indebted to Newton. The intensity of light is
alkaline matter.
nufacturer with whiting, chalk, or some
.other cheap material. i.nveisely as the square of the distance, not that there is less
light at any given. distance,d lint that the same quantity of light
is spread over an increase space.
Another pigmentecalled bichrumate of silver, has been intro-
duced with much success as a waterand
and it would be 'filets much respecting the
physical properties of natural
used more extensively only that it is colour
; being formed
.by artificial light: . Artificial light in. the absence of the. sun is as
Thine colour, almost equal in beauty to Carmine itself. An
ambling a solution of nitrate of silver su
'le"'
of
• It is a beautiful car- indispensable as the-air eve breathe, to the happiness and enjoy-
ment of our various senses; therefore, a substitute fur natural
orange colour may be formed by tnixiiig intr. t ofwith light has been sought after fei n tim eit nen r'• I The ,ene-
with an alkali y
hichromate of potass, but this has beet, d
supersedede mercuryb t°e o. I i ~ DI 10 la . aI.
ral mude of nbtaining it is from the combustion of eel taiwsubs
lour formed by heating chrome yellowstances, which by their burning produce' light. We have
Perhaps, indeed, chrome colours ate altnt.,,t as extensively*h• tguide • • which light '
particularly not mg ui us as to the mode by
e em-
ployed by the dyer and calico printer as by the house painter, cured in ancient times.. 'lt is' probable that it arose from
for they are principally employed in dying prints,l friction, for we know that whole forests have been burned (loon
chrome yellmuiv, acetate of lead is employed as the tem-quint, minit by the friction of one branch against auother, in a heavy gale of
the print being immersed in a *elution of chromate of potass, wind. It is known that if the axle of a coach-wheel were not
we have a chrotnate of lead formed which nothingdestroy,
deo well lubricated the box would take tire. The effects of friction
Some idea of the value of the discovery to our manufacturers are early learned at school. It is known,. that if a button with
may be formed, by. this simple cirentustaoce. The extensive a metal head be violently rubbed such heat is produced, that
manufactory. in tips town uses a great [Mosher of tons of the when the button is slily applied to the hand of his next door
__„,
. chromate of men annually. A manufacturer in Scotland mukes neighhowr, it will burn him. -In cc rage countries rais cmounimin
so touch of the hiehromate of :vows, that he boasts that if the to produce tire by friction, by tubbing two pieces of miry wood
demand emititinues he will dissolve the Shetland Islands. At together, or a cavity is mode in one, piece ,of- won't, whilst
' The most simple trolls new adopted least as melt as made by the other manufacturers of the kings "anther piece is caused to rotate by the action of_ the hands
dein, yet forty-five years ago the material employed in its menu. These modes are not resorted to in more civilized countries.'
Pl li"It
o' i titn.
:.
facture was thrown away as useless and worthless. • ' is by the application of the
consideration tinderriit ionb thanox.
isNow
tre
ntills i
thyu ii
vouchsafedl l e a
We will now shortly' review the green and yellow colours flint
dtleitsietrvaenailmsntereele,
manufactured. in 'tanner times, prior to the discovery of t
chrome colours. TWe k
he chloride of lead was most extensively ewe know that we elicit sparks by the violent concussion of the
pfoyed iu carriage painting. This was made by mixing toga- flint a.mitl steel, which spark. rirep into the tinder-hex and set
Cher the litharge of commerce with about an eqltal quantity of fire to the
_tinder, se that a:brimstone match is inflamed ~ but
cotiyinon salt. These are ihen ground together and allowed to the cells!• or these sparks is nut generally understood In Lon-
retnitin its water for several days; ' A decomposition then takes don it Is the common practice fur pers t. .
o is who sell these flint
stones,.
to stand in '
place. The chorine quits the sodithiaand unites with the lead,the streets at night and strike the flints
against . the. steel, calling
and the oxyeen quits the lead and Unites Withehe.somlium, forni-upon the baestanders. as the sparks
ing soda and chloride of lead. The nines is well washed, amid are emitted, to witness how notch fire their flints eteatain.
The flints contain_ Tin more fire than- the human knuckles, for,
heated to reilne,s, when the product will become hollow. King's
were the knti 'ldes hard enough todetach a portion of the steel,
yellow is chiefly formed from sulphate of mercury. Mercury 1
the same effect n,,,uld be preduced. edatiete 'timmrtimmti of &-
mid sulphuric acid ate heated together and poured into ['oiling ,
'ached metal is a Spherule MA fitaitithhhidiahlif iron; tireda,so
Water, when a yeliew precipitem will- be formed. Queou's eel-
intensely heated heft that it remainehreithithoutil it hes kindled
, few is made by testing for arsenic, and is a Salof
phuret arsenic.
the tinder time heat of which ii'ilien 'tendered fa -It is made - b .
of arsenic, when a yellow precipitate will be thrown downs The I plowing ft to inflame the rimetone of amatch.-.TI The usual
' •
mineral green, called Scheele's green, is a pigment of great substances employed for supporting flame, are tat and bitu-
minous betties. When .we say that we' bunt oil, tallow, or
beauty, but it is not very durable. 'Phis is made by the agency
of arsenic, and the sulphate of copper, in a state of solution. wax, we speelc erroneously, ad they must be first decomposed
These are precipitated by potass in very beautiful flake*, which into their respective eleme.nts, and to do this the presence of
constitute the pigment in question. The other green Which is flame is necessary. If we ware to artiltritheiteee orison at a
still employed fur some purposes, but not very extensively, is white heat, to oil or tallow, we should) merely vaporize
better known by the name of verdigris. It it acetate of i•op them. The same will apply to ether, alcohol -or turnentine ;
p but when we app m w
apply flee e readily decompose these sub-
per, and is formed by the action of vinegar upon metallic cop
per. The most important pigments formed by chemical mean -
stances and obtain a supply of light. After the diecnvery of
phosphorite, it was inside the means or procuring light ; indeed
yet remaining unnoticed are litharge, or protoiide of lead,
miniutn or sesquioxide of load, and the carbonate of lead. The to the present day it is most extensively employed on the Can.
protoxide of lead is formed by heating metallic lead in shallow tinent, especially in France. for that purpose. A 'mall pottier)
'
vessels, when a blue film arises min its surface. The films, which of phosphorus is dissolved in a liquid, and a brimstone match
conititute the protoxide of lead, are immediately rakes,' off its being introduced, is covered with It minute quantity of phospho.
they arise, until all the metal is thus disposed of. 'This is again rim The match is then rubbed upou a piece of-felt, when it
heated, and it becomes the rnessic°t of commerce, which is of takes fire. Sometimes a small tin tube is empleved, into which
a bright yellow colour. BY exposing this protoxide of lead for a stick of phosphorus is forcibly compressed. ava lathe a
twenty-four hour, to a red heat it absorbs half au atom more of better but more expensive tubule of preparing phosphorus. It
oxygen, and becomes sesquioxide of lead, or red lead. The is manufactured into a finely divided state, and mixed with
other and most important compound of lead is carbonate 'a rnagnestui or. lime ; in this state it is carried in a small bottle or
beirl, or white lead. This pigment appears to have been known box, and a small portiou attaching itself to a brimstone match
during the Roman sway, and to have been need as a cosmetic when introduced, is easily ignited, by rubbing it on any 'hard
by the Romeo ladies; it has been used almost time imthem„. : substance. After the diseevery of that woode, nil salt, chlorate
Hal as a pigment. It is made by exposing metallic lead to the et pewits, it was extensively used in Vit ri,,U, U":“1" for the pro-
action of vinegar, and was, therefore, siipposeil to similar to duction of instantaneous light. Chlorate of potash is a cam.
'
acetate of lead or sugar of lead. We fled,. how, ter. that this is pound of chloride acid and potash. Both of the
not the case, thr it is true carbonate. of Iced t--h he vinegar being i &limit! acid are remarkable sopporters of comb constituents of
ustion. It We
shawls evaporated. TO make carbonate of lesel. thentetal must ' mingle a small quantity of powdered loaf sugar with . a small
he cast and -not 'rolled iiito sheets, otherwiee•it will hieimine so i quantity of chlorate of potash. a single drop of sulphuric acid
d ense that the vepistrrirOf the' sinegar trill hmot reedity het tipon Iwill ignite the i
waxturre From this compound many very use_
it: Mesa cast 'sheets eee'then coiled unapirally, add placid on , ful instantaneouslight preparations- lisve been made, and the
end in .pots contidifing viiteelae: •Theie pots ;ire embedded in l first of these wee well known melte French fire box. . In emall
spent bark in order to increase the teniperature, or the Tonto is I vials, at the buttons of. these .boxes, aettitling quantity of sul-
hia ern' tetriferainthe - Itleeft' eantion . must hie' steed j phuric acid :was; ationtained. .th iitlMilkaftigin: ,with asbestos,
inTegultajiting the temperature, otherwise we shall have both
I to Prevent it. from running out of the bottle should the buttie ae

upset. The upper portion of these boxes contained matches
dipped in brimstone, and then in a mixture of sugar and chin-
rate of putass coloured with vermillion. and formed into a paste
with gum- water. Upon these matches being introduced into
the sulphuric acid, they take tire; but it was found that, after
baying used the thatches for a short time, they became useless
in consequence of the sulphuric acid having powerful ten.'
dency to combine with the moisture of the atinespitere, whereby
it became so dittoed as nut to be able to decompose the carbons-
ceous matter with sufficient rapidity to produce combustion.
This may be avoided by putting the bottle before the fire for a
few hours so as to deprive it of the vapour. Mr. Junes, of Lon-
don, has improved upon these French matches by the invention
of prometheans. These matches are composed of pieces of
waxed paper spirally coiled up with one end thinner than the
other; within the larger end there is a small tube containing.
sulphuric acid embedded in a small quantity of chlorate of pot-
ash and sugar. We obtain a tight by striking the larger end
with a hammer. Now by doing this we break the tube, and al-
I low the sulphuric acid to communicate with the compound, and
the waxed !taper takes fire. When we want an instantaneous
light in the ilark, a hemmer is not always convenient, and to
meet this difficulty Mr. Junes has supplied his customers with a
pair of nippers to crush the tube. The only objection to this
mode of obtaining light is'the expense of the materials. Chin.
rate of potash is employed for various operations. This remark-
able salt has such a tendency to undergo decomposition, that it
will combine with other substances, and produce detonations
that are really awful. If we mix it with a portion of the native
sulphuret of antimony in a state of fine division made into a'
paste with water and a snail! quantity of starch, matches made
with it, being first dipped in brimstone, will ignite with a small
degree of friction. It is quite indispensable that the compound
should he mixed in the wet state; by neglecting this precaution
a large manufactory of the matches in LondOrewis blown up.
Mr. Hennaing illustrated this by forcibly triturating some dry
chlorate Of potash with some sulohuret of antimony, when a
powerful explosion took place. The general properties of the
potash and antimony fur making these matches are three parts
by weight of the former to six parts by weight of the latter.
The chief cause of these matches •not lighting when drawn
through sand paper is the weakness of the wood. In Gent-ine,-
where liniber is much cheaper than here, the matches are Endole,
much thicker and stronger, and ignition always ensues. An
article called a slow match is much used in this and other coun-
tries. This slow match is paper or cord dipped into a solution
of saltpetre and gunpowder. It is used for the purpose of light-
ing the pipe or cigar, as it retains tire until the whole is con-
sumed without any flame. A slow match is of great value in
our maitufactures; it is used in mines for the purpose of setting
tiro to a- train of powder used in blasting rocks, in order that, by
its slow but sure combustion, the miner, may have time to se-
cure himself from the effects of the blast. The artillery man
employs them to fire off cannon mid other field pieces. They
were tormerly employed to fire off muskets before fitelocks of
the ordinary description were invented; they were either placed
upon the powder in the touchhole by the soldier, or were at-
tached to a lock, thence called a matchlock, which could be
directed by a trigger to the touchhole. They 'have been super-
seded by the flint and steel, and more recently by the percussion
cap. These slow matches are used by the students at some of
the continental universities. These young gentlemen are worse
than our youngsters; for they smoke in their beds, end, as it
would be inconvenient for them to strike a light every time they
awake, they suspend a piece of slow cord to the ceiling, by
whieh they light their'pipes when they awake.
Mr. Hemming here explained the principle of Dobereiner's
Limp, and cautioned the audience against allowing the platinum
to be acted upon by the gas until the whole of the atmospheric
air had escaped-from tlie•interior, which may be easily managed
by placing a piece of paper between the jet and the spongy 147
tinunt, lest-an explosion should ensue, an instanrevf which he
related, where a Turkey carpet and a number of ladies' dresses
were spoiled.- - We may ignite a piece of Amadou or German
tinder by means of a condensing syringe; but this- ie a trou-
blesome and uncertain operation. Another mode of procuring
light is by meanteof a reddish liquid compound called for chlo-
ride of chromium, which is made by distilling a- mixture of equal
weights of the bichromate of potash and coinmou salt with sul-
phuric acid, when a gas is formed called--the ter chloride of
chromium, which may be condensed in water. , A drop*of this
liquid poured on turpentine, alcohol, ether, sulphur, or other
inflatninahie substances, will cause their instant ignition.
In the lecture of to-morrow evening Mr.-Hemming will con-
sider the means of supplying and continuing the supply of light.

oGfrea!itftißeitaineid, horses,
onthe and
DiscovEnv IN CENTRAL AFRICA.—Doctor. Andrew Sinith,
who Was sent out by the Cape of Good Hope Association into
Central Africa, has recently presented to that body a very in,
terestiug account of his travels. The expedition under him
twenty waqgons,lBth
Atigust, and
startedo head
dn
153,1. returned in the spting of the present year, after
penetrating to the latitude of 23 deg. 26 inin..noith. The rnis-
,,„„ 1,,,..aine acquainted with members of twentr-Seven tribes,
including 180
consistint, of 50 pe,l.tiloi%
and h.,d information of sixteen otherti, and. realised a very ex,
3 379 skins of new or rare
and, two skeletons, twent---
tstl:k.,inrrit.ns.o4is,iicet:::::nenide7u:viiiii!:;:ap,l:,:lic:cio,q.litltitencdstpirtieitiii.)iemidnes.n,nas,tuarinleihiis)tticieryi,,ackage
birds, three barrels of snakes and liz iris, 'brie box of insects,
y•three new and rare
dried'
plants. They also ascertained that the Hottentot race was
much more extended I than has, hitlie:to, twen' believed. and that
parties or communities belongin4 to it inhabit the interior as
far its the inland lake, which they were told Was, egt less than
three weeks' journey to the north of the tropic of Capricorn.