ON SULPHURIC ACID. 
237 
arsenic, although a portion may be reduced during evapora- 
tion, by the agency of the phosphorous and nitrous acids, 
but principally by the phosphuretted hydrogen which is 
developed. It results from this that a perfect purification of 
this acid cannot take place without the agency of sulphuretted 
hydrogen. I may add, that I have never detected arsenic in 
the water in which phosphorus has been kept. 
But, if sulphuric acid containing arsenic is pernicious in 
pharmaceutical preparations, it should also be in the extrac- 
tion of tartaric acid. In fact we have found arsenic in the li- 
quor from which tartaric acid has been separated by crystalli- 
zation. Nevertheless, we have never detected arsenic in the 
tartaric acid of commerce, which is generally in large and 
handsome crystals, although it may have contained lead. All 
these facts prove that too much attention cannot be paid to 
the chemico-pharmaceutical products as they exist in com. 
merce. 
In a report made to the Royal Academy of Medicine, we 
have made known the fact that the sulphuric acid prepared at 
Lyons from pyrites contains arsenic. 
Journ. fie Chirn. Med. 
