454 
DE. A. W. HOFMAXy OX THE PHOSPHOEHS-BASES. 
as I shall have to allude to them in the course of the memoir. It is. however, worth 
while to mention in this place that, when the experiment is made with pure substances, 
and under the conditions above mentioned, the two bromides described are almost the 
only products of the reaction. 
These two bodies have become the starting-points of two extensive groups of com- 
pounds, which may even now be distiaguished as the series of monatomic comjyounds, 
and the series of diatomic compounds. 
I now proceed to the detailed description of the indi-vidual members of these series. 
SEEIES OE MONATOMIC COMPOUNDS. MONOPHOSPHONIIEM COMPOUNDS. 
Salts of Beomethyl-teiethtlphosphoxioi. 
Bromide of Bromethyl-triethylphosphonium. — By this long name I designate the ciy- 
stalline substance which is produced by the union of one molecule of dibromide of 
ethylene and one molecule of triethylphosphine. The preparation of this compound 
has already been given in the preceding paragraph. It is the chief product of the 
reaction when the dibromide of ethylene is in excess. 
The equation 
C 2 H 4 Br^+Ce P = Cg K,, P Br, 
requires about I vol. of dibromide of ethylene to I '5 vol. of triethylphosphine ; but even 
when a larger quantity of the bromine-compound is heated with the phosphorus-base, 
both in presence or absence of ether or alcohol, we always obtain an appreciable quan- 
tity of the second bromide. It is only by allowing an immense excess of dibromide to 
act at the common temperature upon triethylphosphine, either in presence or absence of 
ether, that the formation of the second bromide is altogether avoided. In this reaction, 
which is not complete in less than twenty-four hours, a considerable quantity of gas is 
evolved, which does not appear when the substances are heated together. 
To purify a product, which contains appreciable quantities of the second bromide, it is 
necessary to crystallize it at least three or four times from absolute alcohol ; in the last 
crystallization it is desirable to mix the alcoholic solution until a moderate quantity of 
ether. The solution, if left to itself, frequently deposits separate well-defined crystals, 
which may be dried without decomposition at 100°, and which melt at about 235° with 
partial decomposition, hydrobromic acid being abmidantly evolved. The bromide, 
purified in the manner just described, gave on analysis the following numbers : — 
I. 0‘5630 grm. of bromide gave 0’6521 grm. of carbonic acid and 0'3173 grm. of 
water. 
II. 0'4926 grm. of bromide, precipitated by nitrate of silver, gave 0'3004 grm. of 
bromide of silver. 
A simple experiment showed that nitrate of silver precipitates from this compound 
