July £0. 1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
45 
tures or wounds made in the leaves and young 
branches of E. virnuutlis. It consists principally 
of grape sugar containing about (5 per cent, of man- 
nite. The other variety is the secretion of a hemi¬ 
pterous insect, and is found at certain seasons in 
abundance upon the leaves of E. dumosa. It is in 
little white or yellowish cones, covered with woolly 
filaments, in which are deposited the larvae of the 
insect. 
THE CHEMISTRY OF THE HYDROCARBONS.* 
BY C. SCIIOBLEMMER, E.B.S. 
[Continued from page 27.) 
Olefines .—By abstracting two atoms of hydrogen from 
the paraffins we obtain the second group of hydrocarbons, 
called by Guthrie the olefines. 
These olefines exhibit in their physical properties, as 
specific gravity, boiling-points, etc., great resemblance 
to the corresponding members of the paraffin series. 
They are, however, easily distinguished from the latter 
by the fact that they combine with great energy with 
the elements of the chlorine group, for which reason 
they have also been called non-saturated hydrocarbons. 
To account for their constitution there exist three hy¬ 
potheses :— 
1. They contain carbon atoms with free combining 
units. 
2. One of the carbon atoms is no longer a tetrad, but 
a dyad. 
3. One carbon atom is linked with two combining 
units to two combining units of another. 
The first hypothesis found many adherents some years 
ago. Amcngst these, Lothar Meyer has very clearly 
stated the reasons why the hypothesis that the so-called 
non-saturated compounds contained free combining- 
units was much more probable than the view adopted by 
Kekule, that a double linking of carbon atoms occurred 
in them. He says (‘ Ann. Chem. Pharm.,’ cxxxix. 285) 
“ that in the first place this hypothesis offers no philo¬ 
sophical difficulty; that it cannot be astonishing that 
under certain conditions one or more affinities remain 
unsaturated; on the contrary, it would be wonderful if 
such non-saturated affinities did not exist.” 
“ For certain compounds this theory is even unavoid¬ 
able, as for nitric oxide, carbonic oxide, the vapour of 
mercury, cadmium,” etc. 
Now, according to this theory, the most simple ole¬ 
fine known, ethylene, C 2 H 4 , ought to exist in two iso¬ 
meric forms, viz. :— 
CH, 
carbon is proved in such a simple case, the same assump¬ 
tion is. at least admissible in more complicated cases. 
Kekule, in conjunction with Zincke, therefore repeated 
Harnitzky’s experiments (‘Ann. Chem. Pharm,’ cLxii. 
125). They, said that from their theoretical stand¬ 
point, the existence of chloracetene not only appeared 
improbable, but that the properties ascribed to this body, 
as well as the reaction by which it was formed, were so 
remarkable that it appeared necessary to make the per¬ 
sonal acquaintance of chloracetene. Although it ap¬ 
peared improbable that this body was really isomeric 
with Regnault’s vinyl chloride, yet it might be a poly- 
meride, which by dissociation yields a lighter vapour. 
It was also possible that vinyl chloride had not been 
obtained in a pure state, and was identical with chlor¬ 
acetene, and there was also the probability that all the 
statements about this latter compound were erroneous. 
The result of this investigation was that the last view 
was the correct one. They found that the most remark¬ 
able property of this remarkable compound was its non¬ 
existence. 
According to the theory of dyad carbon, only one 
ethylene can exist having the constitution CH 3 —CH. 
But that the known ethylene has not this constitution is 
proved by the fact that its chlorhydrin yields by oxida¬ 
tion monochloracetic acid (‘ Zeitschr. f. Chem.’ [2], vii. 
263). 
Another proof against the existence of free combining 
units, or of dyad carbon, is found in the fact that only 
one propylene is known, of which hydrocarbon four 
modifications ought to exist, according to the theory of 
free combining units, viz.:— 
ch 2 - 
CH,— 
CH= 
ch 3 
1 
1 
CH,— 
| 
CH— 
| 
CH,- 
1 
c= 
| 
ch 2 - 
ch 3 
| 
ch 3 
1 
ch 3 
CH= 
C o— 
I 
CH,— 
However, experiments made by Meyer and by Tollens 
for the purpose of obtaining an isomeride of ethylene 
failed. But although the two isomeric modifications of 
ethylene have not been obtained, yet it was stated that 
two different chlorine-substitution products of ethylene 
exist, viz., monochlorethylenc ox vinyl chloride, obtained by 
Regnault, and chloracetene , which Harnitz-Harnitzky 
prepared by the action of phosgene upon aldehyde. As 
both compounds had been repeatedly investigated by 
other chemists, their existence could hardly be doubted, 
and could only be explained either by assuming free 
affinities or by the theory of dyad carbon. The exist¬ 
ence of a compound isomeric with chlorethylene is cer¬ 
tainly of the highest importance to the theory, because, 
as Kekule has pointed out, if the existence of dyad 
* A lecture delivered before the Chemical Society, April 
4th, 1872. Reprinted from the ‘ Journal of the Chemical 
Society’ for June, 1872. 
or only the latter two in the case of the dyad carbon 
theory. 
Friedel and Ladenburg, as 'well as Butlerow, failed to 
obtain an isomeride of common propylene. The two 
former chemists tried to obtain the last of the four 
forms by acting with sodium upon the so-called methyl- 
chloracetol, CH 3 —Cd 2 —CH 3 , but obtained, instead of 
it, only the well-known propylene, which was formed 
by a molecular change taking place. 
From these and other examples, we must conclude 
that the olefines contain neither dyad carbon nor free 
combining units, and that they are really saturated 
compounds, containing two carbon atoms linked together 
by two combining units of each. 
Butlerow has some time ago added a fresh proof of 
the correctness of this hypothesis; of this I shall have 
to speak when I come to the next group. 
The number of isomeric olefines capable of existing is 
larger than that of the corresponding paraffins, as the 
double linking of the carbon atoms can take place in 
different parts of the hydrocarbon. Thus there exist 
only two butanes, but three butylenes, viz.:— 
CH 3 
CH, 
H 3 C\ 
H,C/ 
-CH,—CH=CH, 
-CH=CH—CH 3 . 
■ CCH,. 
The number of isomerides known is, however, not 
large at present; nearly all those which have been better 
investigated contain the two carbon atoms, which are 
linked together by two combining units situated at the 
end of the chain. These may therefore be considered as 
being derived from ethylene by the substitution of a 
monad alcohol-radical for one atom of hydrogen, thus:— 
CH, 
II 
CH, 
CH.CH, 
CH, 
cii.c,h 5 
II 
CH, 
CH f — s 
II ( 
CH, 
CH, 
CD! 
