The sun., 1900-12-30

4
the ordinary phosphate Of commerce pos
sessed. according to him. the formula
! Pos. 2Na.O. HaO: two thirds OF the "water
| of constitution" being replaced by oxide Of
sodium. Liebig. then professor at Giessen
! Gso3-is7Sl. founded on these and on similar
| observations OF his own the doctrine Of
! polybasic acds-acids in which one. two.
three or more atoms Of hydrogen were
| repaceable 10y metals Thus. instead OF
| writing. as Graham did. Pos. 2Na,O. H,O.
he wrote PO.NaiH; and for orthophos-
| phorc acid PO.H,. The group OF atoms
| PO. therefore existed throughout the
whole series of carbohydrates. and
| could exist in combination with hydrogen.
with hydrogen and metals or with metals
| alone. Similarly the group P,O,) was
| characteristic OF pyrophosphates and
| POs Of metaphosphates. for Pos. 2HsO
| PiO,)H.: and Pos H,O=2POIH.
CLEAR IDEAS OF THE STRUCTURE OF THE
MoLEcULE.
The first clear ideas of the structure
| Of the moecue were. however, gained
from the study Of the compounds Of carbon.
! II was difficult to apply the dualistic the
ory to them. For few OF them are elec-
trolytes. and therefore their products OF
electrolysis, being non-existent. could not
be classified. Nevertheless Gay-Lussac.
regarded alcohol. Calico. ~ a compound
Of C,H.. ethylene. and H1O. water: and
oxalc acid Canhydrots) Cos. as one OF
Goa with co. The discovery OF "isomerio
compounds" l. e.. of compounds which
possess the same ultimate formula and
yet differ entirely in their properties forced
upon chemists the necessity of attending
to the structure Of the molecule. for only
by such supposition could the difference
between two isomeric bodies be explained.
In 1923 Ilebg discovered that silver full
inmate and silver cyanate both possessed
the empirical formula AgCNO: in 1928
this was followed by the discovery by
Faraday that oil gas contains a hydro
carbon idenacal In composition with ethyl
enc, C,H. yet differing from it in proper
tics; and in 1929 Wohcr. professor in Cot
tingen nsOO-lsS2l. discovered that urea. q
constituent of urine. could be produced
by heating ammonium cyanate. NH.CNO.
substance Of the same d formula IL
therefore became clear that the identity Of
compound must depend on some other
cause than its ultimate composition.
In 1888 Lebig and Wohler took an i'm
portant step in eucidating this question
by their invest cations on benzoic acid. an
acid obtainabe by distilling resin named
gum benzoin. They showed that this
acid. C7HsO7, could be conceived as con-
sisting Of the group CLIO. to which they
gave the name "benzoyl." in combination
with OH; that benzoic aldehyde. CLIO.
might be regarded As its compound with
hydrogen; that it also formed compounds
with chlorine and bromine and sulphur.
and replaced hydrogen is ammonia
Clio NIl,). They termed this group BEN
zoyl. compound element or "radi-
cal" This research was followed by one
by Robert Bunsen. professor at Heidel-
berg born in 1911. and recently uS9e) dead,
which bore reference TO cacodyl, a com.
pound OF arsenic. carbon and hydrogen,
in which the idea Of radical was con-
firmed and amplificd.
The idea Of a radical having thus become
established. Jean Baptiste Andree Dumas.
professor in Paris nsOo-iss4). propounded
the theory Of " substitution" l. e., that an
element such as chlorine or OXYGEN (which,
be 1t noticed, il electro-negative on Ber-
zelus's scale) could replace hydrogen
in carbon compounds. atom for atom.
the resulting compound belonging to tho
same type" as the one from which it
was derived And Laurent. warden Of
the mint at Paris Qso7- 1889 and Gerhardt.
professor at Montpelier and at Strassburg
(islo-is5e). emphasized the fact that one
element. bo 1t what it may. can replace
It's chemical character. and also that an
atom OF hydrogen can be replaced by q
group Of atoms, or radical. behaving fol-
the occasion like the atom Of an element,
II is to Laurent and Gerhardt that We owe
the definition of an atom--ths smallest
quantity Of an element uhich cdn be present
in a com pound: an equivalent-that peipld
OF an element uhich combines pith or re-
places one part by ueieh Of hydrogen. and
a molecule-he smallest gudntity uhich
can erist in free state, Whether Of an ele-
nert or compound. They recognized,
too. that molecule Of hydrogen. chlorine,
&c. consists Of two atoms.
POWERS OF COMBINATION.
In ls4s Wurtz. professor In Paris usl7.
1884, and Hoffman,. then professor In
the College OF Chemistry in London, after.
ward at Berlin Osls-1s92). discovered
series Of compounds allied to ammonia,
Mis-. in which one or more atoms OF by.
drogen were replaced by a group, or radi-
cal. such as methyl CHI. ethyl (CaH3.
OF phenyl (C,HS). Wurtz referred such
compounds to the ammonia type They
all resemble ammonia in their physical
properties-smell. taste. &c.-as well 40
in their power OF uniting with acids to
form salts resembling ammonium chic.
ride (NH.CD, and other ammonium COM
pounds. Shortly afterward williamson,
professor at University College. London
us55-s7), added the water type" in con-
sequence Of his researches on mixed
ethors"-bodies in which the hydrogen
of water might be regarded as replaced
by organic radicals. Thus we have
the series. H.O.H: CHsO.H: CH,. Chs: