1887.] Prof. Letts and W. Wheeler on Benzyl Phosphines, 69 
a stream of hydrogen, the phosphine is obtained of the constant boil- 
ing point, 180°. 
Our own experiments, repeated again and again, and with the 
greatest care, have satisfied us that the pure phosphine cannot be 
obtained thus readily. In our attempts to obtain it by simple 
fractional distillation, we operated altogether upon 50 to 60 grms. of 
the crude substance. The phenomena observed were much the same 
in each case. The crude products began to boil at about 100°. The 
thermometer then rose rapidly to 160°. From 160° to 170° most 
distilled, whilst from 170° to 190° very little passed over. The 
residue in the retort usually decomposed suddenly above this 
temperature, with separation of red phosphorus. All the fractions 
contained the primary phosphine, for they all had its powerful 
and characteristic odour, and when mixed with fuming hydriodic 
acid they all gave the crystalline hydriodate. On repeatedly re- 
distilling them no substance of constant boiling point could be 
obtained. Considering that the boiling point of chloride of benzyl 
is 177°, and that much of that body is contained in the crude phos- 
phine, it is not surprising that mere fractionation fails to separate it 
from a body boiling only a few degrees higher. 
Eventually we decided to separate the phosphine from the crude 
product by obtaining its crystallised hydriodate, but ownng to 
the bulky nature of that compound and to its insolubility, we 
experienced considerable difficulty in effecting this. After several 
experiments, we found that either of the two following methods 
may be employed : — 
(1) The crude phosphine is placed in a retort and a stream of 
perfectly pure hydriodic acid gas (dried by passing over phosphoric 
anhydride) is conducted by a long tube into the body of the retort. 
As soon as saturation seems to be complete the retort is placed in 
an oil bath, and heated to a temperature of 160° to 180°, a very slow 
current of hydriodic acid passing all the time. The hydriodate then 
sublimes in beautiful colourless scales, and when most has thus 
volatilised into the neck of the retort, the latter is allowed to cool — 
the hydriodate shaken out, and well-washed with pure benzol. 
(2) The crude phosphine is mixed with about twenty times its 
volume of pure dry benzol, and the mixture satured with dry 
hydriodic acid. It grows w^arm, and eventually almost solid from 
