PURIFICATION OF SULPHATE OF IRON. 
155 
mated silver ; there is therefore a loss of 120,000 kilogrammes of 
mercury, worth at least one million of francs, which loss the new 
process avoids. 
5. Public Health. — In the new process there is no loss of mercu- 
ry ; the mercurial vapor is condensed with the vapor of water ; fur- 
ther, in the common operation, mercurial vapor fills the whole of 
the apparatus, and when it is opened at the close of the operation, 
the vapor is diffused in the atmosphere ; whereas in the new pro- 
cess the vapor has driven all metallic vapor from the apparatus, 
and there is no danger in opening it. Thus our operation is com- 
plete, and the employment of high pressure steam seems to have ef- 
fected the long sought solution of the problem, of perfectly preserv- 
ing the workmen fom the mortal attacks of mercury in the numer- 
ous and important uses in which this metal is distilled. — Chem.Gaz. 
Dec. 16, 1851, from Camples Rendus. 
ON THE PURIFICATION OF SULPHATE OF IKON OF COMMERCE 
TO FIT IT FOR MEDICINAL PURPOSES. 
By M. Thorel, (D'Avallon). 
M. Thorel, in the Journal de Pharma Ae for Nov., 1850, points 
out a mode of treating commercial sulphate of iron (copperas), so 
as to free it from its most usual impurities as occurring in France. 
He states that bi-tartate of potassa, boiled with an impure solu- 
tion of proto-sulphate of iron, will precipitate the zinc as an in- 
soluble tartrate of potassa, zinc, and iron. He further ascertained 
that neutral tartrate of potassa precipitates manganese from the 
sulphate as an insoluble tartrate. The copper is separated by 
boiling the solution with iron filings and a little sulphuric acid, 
which also brings the sulphate completely to the state of a proto- 
salt. The following is his formula. 
Take of Copperas, 3000 parts. 
Iron-filings, 90 " 
Sulphuric acid, 20 " 
Water, 8000 " 
Put the whole in a cast iron boiler and heat to ebullition, stir- 
ring continually. Half an hour's boiling is sufficient to decompose 
