Dr. Hofmann on Phosphammonium Compounds. 307 
Ther are other products formed, resulting from secondary reac- 
tions. 
It was not quite easy to obtain a sufficiently satisfactory experi- 
mental foundation for the diatomic nature of the second compound. 
This substance presents an extraordinary degree of stability; in its 
general characters it is closely allied to the numerous monatomic 
bromides, both of the nitrogen- and of the phosphorus-series, which 
in the course of these researches have come under my consideration. 
Lastly, the oxygenated derivative of the bromide resembles so per- 
fectly the monammonium- and the monophosphonium-bases, that 
more than once during my experiments I was inclined to doubt the 
correctness of my interpretation. 
There is no direct proof of the diatomic character of the com- 
pound. Why should we reject the simple formula deducible from 
experiment? The hydrocarbons C, H, are very prone to molecular 
transformations without change of composition. The idea suggested 
itself, that the diatomic saline molecule might be split into two 
monatomic saline molecules, 
[(C, H,), (C, H,)" P,}" Br, =2([(C,H,), (C,H)! P] Br). 
It is true C, H, figures in this formula as monatomic, whilst we 
should expect it endowed with diatomic substitution-power. But 
the connexion between composition and substitution-power is by no 
means finally settled; in fact, we know of many cases in which, 
under conditions not sufficiently established, the atomicity of a mole- 
cule changes: witness the radical “ allyle,” which is capable of re- 
placing one or three equivalents of hydrogen. 
But without going this length, the scission of diatomic ethylene 
into two monatomic molecules may take place in many other ways. 
The transformation of dibromide of ethylene into hydrobromic acid 
and bromide of vinyle, 
(C, H,)" Br,=HBr+(C, H,) Br, : 
is a familiar example. The splitting of the ethylene-compound into 
bromide of formyle and bromide of methyle, 
(C, H,)" Br,=(C, 1) Br+ (C, H,) Br, 
has never been observed, but did not appear altogether unlikely. 
Our analytical methods are insufficient to distinguish between 
[(C,H,), (C, H,) P] Br and [(C, H,), (C, H) P]B§ ; 
and what I have represented as a diatomic ethylene-compound 
might have been, after all, a monatomic bromide—the bromide of 
formy]-triethylphosphonium, the complementary methyle-compound 
[(C, H;), (C, H,) P] Br 
existing possibly among the secondary products of decomposition. 
In the presence of these and several similar self-raised objections, 
by which every observer endeavours to test the truth of his con- 
clusions, I was induced again to appeal to experiment. 
The prosecution of this line of the inquiry has led me to the disco- 
very of a new class of diatomic bodies, which, while it confirms incon- 
testably the correctness of my interpretation, appears to claim the 
attention of chemists for several other reasons. 
