294 BUNSEN ON THE CACODYL SERIES. 
The difference as regards the sulphur, which is scarcely 1 per — 
cent., is easily explicable from the unavoidable loss in oxidation 
by means of nitric acid. 
The facility with which the sulphuret of cacodyl is oxidized, 
renders it impossible to determine the specific gravity of its va- 
pours by Dumas’s method; and, in short, an approximation is 
all that can be obtained by Gay-Lussac’s method, in consequence 
of the temperature, 200°, approaching so nearly the point at 
which the substance is decomposed with the formation of sul- 
phuret of mercury. 
The following result was obtained from a very carefully con- | 
ducted experiment :-— 
Substance employed . . . . . 0194 grm. 
Barometer. . . 328 lines. 
Mercurial pressure (to be Setincted) 48°9 
Temperature. . «is « + - » 215” Genie, 
Volume of vapour. . - os Sarees 
The specific grav i aititeate from the above, after making 
every correction, is 7°72, and that estimated is 
A vole toerban }) seks p'a Loy BETH 
195." Hydrogen... »- + «6 ) 8256 
B32) Apeeiie: cece cer joe (fe GRE 
1vol. Sulphur . . . . . « 22180 
16°7802 = 2 = 8:39. 
Although the difference between the calculated and observed 
specific gravities amount to nearly one-tenth, it is fully explained 
from the circumstances already noticed ; and I think the result 
justifies me in concluding that the relative condensation of the 
sulphuret of cacodyl agrees with that of the oxide. 
3. Seleniet of Cacodyl. 
This compound is formed in a similar manner to the corre- 
sponding sulphuret. Pure chloride of cacodyl must be distilled 
two or three times with a solution of seleniet of sodium. 
KdCl) _ f Kd Se 
Na So a hae Cl 
The liquid which passes over with the aqueous vapour has a 
yellow colour, and collects at the bottom of the receiver in the 
form of heavy oily drops. The mode of purifying is the same 
as that employed with the sulphur compound. 
