194 Proceedings of Royal Society of Edinburgh. [sess. 
the two reactions are complementary to each other. Among the series 
to which he extended his investigations was that of benzyl, and in 
a paper published in the Berichte of the Berlin Chemical Society* 
he describes the preparation of mono- and dibenzyl-phosphine, and 
gives their properties. Dibenzyl-phosphine he isolated as a crystal- 
line substance perfectly tasteless and odourless, insoluble in ether, 
but soluble in alcohol. Its melting-point he found to be 205° C. 
In a paper read before this Society (19th December 1887), one of 
us, in conjunction with Mr W. Wheeler, describes further investiga- 
tions on this body, and shows that it forms a series of compounds 
of a somewhat remarkable nature for a secondary phosphine. This 
fact, and some other properties of the substance, led to the suspicion 
that it was not dibenzyl-phosphine at all, but the oxide of tribenzyl- 
phosphine. Accordingly the investigation was re-opened with Mr 
R. F. Blake, and its course has been as follows : — 
1. On carefully re-crystallising the substance from alcohol, its 
corrected melting-point was found to be 216-216*5° C., while that 
of two specimens of oxide of tribenzyl-phosphine (prepared by two 
different methods) was found to be the same. 
2. Very little difference exists in the percentage amount of carbon 
and hydrogen in dibenzyl-phosphine and oxide of tribenzyl-phos- 
phine, as the following numbers show : — 
(C 7 H 7 ) 2 HP (c 7 h 7 ) 3 po 
Carbon =78*50 78*75 
Hydrogen = 7*01 6*56 
Consequently it would not be possible to decide with absolute 
precision between the two substances by a mere combustion. On. 
the other hand, there is a considerable difference between the two 
bodies in their percentage of phosphorus : — 
(C 7 H 7 ) 2 HP (C 7 H 7 ) 3 PO 
Phosphorus =14*48 9*69 
Unfortunately, however, as we have again and again found, the pro- 
cesses for phosphorus determinations in ordinary organic substances 
are absolutely untrustworthy when applied to phosphines. A new 
method was therefore necessary, and after many trials we believe we 
have found one which is perfectly accurate, trustworthy, and capable 
* Berichte (1872), v. 100. 
