12 
Selected Articles. 
arsenious acid present. The zinc remains in solution. By- 
boiling, the sulphuret of arsenic collects in yellow flakes, 
which, having been collected and washed, are to be heated 
by the means proper to reduce it to a metallic state. By this 
method one-tenth of a grain of arsenious acid may be de- 
tected in half a pound of alimentary matters.* 
To reduce the sulphuret of arsenic, I make use of a very- 
simple process, which will give evidence of arsenic in the 
most minute portion of the sulphuret. This consists of intro- 
ducing the sulphuret into a glass tube of three inches in 
length, and closed at one of its extremities, and placing di- 
rectly above the sulphuret a piece of leaf silver rolled 
into a ball. The closed extremity of the tube is to be heated 
by means of a spirit lamp. A decomposition immediately 
takes place, the sulphuret is volatilized and decomposed, the 
sulphur entering into combination with the silver, whilst the 
arsenic condenses in a metallic state in the form of a brilliant 
blackish gray ring, a little above the heated portion of the 
tube. 
If instead of reducing the sulphuret to a metallic state, it is 
wished to transform it into arsenious acid, instead of the leaf 
silver, the oxide of that metal is to be used. The decompo- 
sition takes place very rapidly at a somewhat elevated tem- 
perature, the arsenious acid which is produced condenses to- 
wards the upper part of the tube, in small, white, octahasdral 
crystals, which may be readily detached. If the acid be in 
so small a quantity that it would be impossible to detach it, 
by reversing the tube, the sulphuret of silver, which has melted 
into a small solid mass, will fall out. Distilled water is then 
to be poured into the tube, and on the application of heat, the 
arsenious acid will be dissolved, when the solution can be 
tested by the proper reagents. 
Journ. de Pharm. 
* The operation also succeeds by using a solution of sulphate of zinc, and 
then adding- potash or subcarbonate of soda in excess, instead of making use of 
the solution of oxide of zinc. 
