292 BUNSEN ON THE CACODYL SERIES. 
oxidation can take place while the gas is present. The water 
and excess of sulphuretted hydrogen are separated by chloride of 
calcium and carbonate of lead. The access of the air must be most 
carefully prevented as soon as the lead salt causes no black co- 
loration, and especially in filling the distillation tube. In this 
latter operation the substance is entirely freed from any persul- 
phuret of cacodyl which may possibly have been present, which 
remains behind in the leg of the tube in the form of a yellow, 
nauseous, viscous fluid mixed with some crystalline grains. 
This substance can also be procured in large quantities from 
the acid liquid which is obtained in the preparation of the fluid 
of Cadet. The large proportion of oxide of cacodyl which remains 
dissolved in the acetic acid in that liquid, can be precipitated as 
sulphuret of cacodyl by adding the sulphur salts already men- 
tioned; for this substance is nearly as insoluble in that acid 
liquid as in water. The decomposition which takes place is as 
follows :— 
Kd O Kd S$ 
Ba '+ 8H f= | Bo4a 
SH 
The formation os this Fees compound from alcargen (caco- 
dylic acid), is perhaps more interesting in a theoretical point of 
view than useful as a means of preparing it for research. The 
same phenomenon is observed in conducting a current of sul- 
phuretted hydrogen through an aqueous solution of cacodylic 
acid, as takes place with many inorganic oxides; as for example 
arsenic acid, which is reduced with the separation of sulphur 
and formation of its sulphur compound. 
Kd O, + aq peo 
4SH apes 
Persulphuret of cacody] is ines on tks contrary, when we 
use an alcoholic solution, because the sulphur which separates 
immediately combines with the sulphuret of cacodyl. 
Sulphuret of cacodyl is a limpid zthereal liquid, which does 
not smoke in contact with the air, and has a most penetrating 
offensive odour, which is very similar to that of mercaptan and 
alcarsin, and adheres for a long time to any substance. It does 
not solidify at a temperature of — 40° C. It distils over with © 
water, although its boiling point is considerably higher. When 
it is heated to redness in a glass bulb, it deposits the vapours of — 
