DE. A. W. HOEMAJ!^N ON THE PHOSPHOEIJS-BASES. 
471 
On comparing the composition of the two bromides which are formed from dibromide 
of ethylene by the fixation of one or two molecules of triethylphosphine, it could scarcely 
be doubted that the monatomic compound, even when already formed, must still be in a 
condition to take up the second molecule of triethylphosphine, and thus to pass into 
the diatomic bromide. The correctness of this supposition is easily established by expe- 
riment. The monatomic bromide acts strongly, even at ordinary temperatures, on a 
fresh quantity of the phosphorus-base, being transformed, with evolution of heat, into 
the diatomic compound 
C3 H., P Br, + C, P = C„ H,, P^ Br^, 
In presence of alcohol and at 100°, the reaction is completed in a few seconds. With 
lively interest have I followed up the result of this simple experiment ; for its success 
ob\iously pointed to a soui’ce from which an almost incalculable number of diatomic 
compounds of the most varied composition might be obtained. For this reason I have 
not omitted to establish by numbers the conversion of the monatomic into the diatomic 
bromide, and in the following sections I shall have frequent occasion to cite analytical 
results, which leave no doubt as to the facility of this transformation. 
The molecular constitution of the new bromide is satisfactorily represented by the 
formula 
^14 H34 ^2 
(C2H5)3PT 
(C2H3)3PJ 
Brg. 
The salt is derived from a diatomic metal, a diphosphonium, in which 6 equivs. of 
hydrogen are replaced by 6 equivs. of ethyl, and the remaining 2 equivs. of hydrogen 
by the radical ethylene indivisible under the given circumstances. It is the diatomic 
character of the ethylene that links together the two molecules of triethylphosphine, 
and gives to the new molecular system the necessary stability. 
The dibromide is very easily attacked by silver-compounds, and in this manner an 
extensive series of very sharply characterized diphosphonium-salts may be obtained, many 
of which crystallize remarkably well. In these reactions, however, a tendency towards 
the formation of double compounds is frequently observed, and hence it is for the most 
part better to prepare the salts by treating the free base with the corresponding acids. 
In examining the dibromide, I have made some observations which I may take an 
opportunity of pursuing further by and by. When the aqueous solution of this salt 
is mixed with bromine-water, very beautiful yellow needles are immediately separated, 
consisting of a polybromide. These needles may be recrystallized from boiling water, 
but, it appears, not without decomposition. They have but an ephemeral stability. On 
boiling the compound, bromine continues to be evolved, and ultimately the original 
bromide is left behind. Polybromides, of exactly similar character, are formed by the 
action of bromine on the bromides of all the ammonium- and phosphonium-bases that I 
have examined. 
I have already pointed out that, in fixing one molecule of triethylphosphine to form 
