BUNSEN ON THE CACODYL SERIES. 291 
ting to dryness, we obtain a substance, which, when heated to 
redness in a glass tube, emits the repulsive odour of alcarsin. 
This odour is changed into the no less characteristic one of the 
chloride of cacodyl, by moistening the inside of the tube with a 
few drops of chloride of tin. Oxide of antimony does not react 
in the same way. The oxide of cacodyl can also be employed 
to detect acetic acid salts in mixed liquids, by treating the same 
with potash and arsenious acid, evaporating, and heating to red- 
ness: the addition of potash is necessary, because alcarsin is 
only formed from the acetate of the alkaline bases. 
2. Sulphuret of Cacodyl. 
This substance is obtained by distilling a mixture of chloride 
of cacodyl and hydrosulphuret of barium in solution, when a 
great escape of sulphuretted hydrogen takes place. The sulphur 
compound passes over as soon as the temperature rises to the 
boiling point, while chloride of barium remains behind in the 
a 
retort. 
Kd Cl Bas 
S+SH Sea 
Sulphuret of barium will not answer, reid the chloride of 
cacodyl generally contains some oxide of cacodyl mixed with it, 
which is decomposed by sulphuretted hydrogen and not by sul- 
phuret of barium. It is therefore necessary to employ the above 
salt in order to obtain a product free from oxide. A small quan- 
tity of a viscous offensive matter, which consists of sulphur and 
a solution of the persulphurets in protosulphuret of cacodyl, re- 
mains behind in the retort ; it is formed at the expense of the 
hyposulphuret of barytes and the bisulphuret of barium, with 
which the salt employed above is usually mixed; for in the de- 
composition of these mixed products the uncombined sulphur 
combines with the protosulphuret of cacodyl and forms the solid 
persulphuret. The sulphuret of cacodyl dissolves any sulphuret 
of iron which may be present of a blue colour: the distilled 
fluid however does not possess this colour. It is necessary to 
distil it a second time with the sulphur salts to ensure a perfect 
decomposition. The access of the air need not be so carefully 
prevented so long as the liquid is covered with a layer of water 
holding sulphuretted hydrogen in solution, because that gas de- 
composes any oxidized product of the cacodyl, and therefore no 
