180 ON PURIFYING ARSENIFEROUS SULPHURIC ACID. 
ART. XLTX.— ON A METHOD OF PURIFYING ARSENIFEROUS 
SULPHURIC ACID DURING ITS MANUFACTURE. 
By M. Alph. Dupasquier. 
Arsenical sulphuric acid is prepared in several large 
manufactories in France and England by the calcination of 
pyrites (sulphurets of copper and of iron more or less mixed 
with sulphuret of arsenic and arseniuret of iron.) 
From the experiments and observations contained in this 
memoir it results — 
1. Tiiat the use of arseniferous sulphuric acid in the 
arts, and in the production of chemical and pharmaceutical 
preparations, may lead to serious disadvantages and dan- 
ger. 
2. That arsenic in the sulphuric acids of commerce is in 
the state of arsenic acid. 
3. That the proportion of this poison in the acid varies, 
but that it may be estimated at about 1- or li-thousandth. 
4. That the employment of hydrochloric acid or sulphu- 
retted hydrogen is insufficient for the purification of arseni- 
ferous sulphuric acids. 
5. That the use of alkaline sulphurets offers a complete 
and ready method for the purification of the arseniferous 
acids. 
6. That the sulphuret of barium, both as regards economy 
and the purity of the sulphuric acid, is by far preferable to 
the other alkaline sulphurets, and it is moreover cheap and 
very easy to put in practice during the preparation of sul- 
phuric acids in the manufactories.* 
Ibid from Comptes Rendus. 
*By the employment of this method, not only is the arsenic entirely 
eliminated, but the nitric acid is also necessarily destroyed, an acid 
which occurs in most of the sulphuric acids of commerce. 
