1819.] Dr. Vest on Vestium. 345 
tions ; for the ore is very frequently mixed with calcareous spar. 
The pounded ore is mixed simply with pulverized glass, and put 
into a good air furnace, and exposed for an hour to a sufficient 
heat. A heat amounting to about 40° Wedgewood will be suffi- 
cient for the purpose. 
The regulus is pulverized and digested on a sand-bath with 
nitric acid till all extrication of gas is at anend. The solution is 
renewed by the addition of a little muriatic acid. But as this 
acid dissolves a great deal of iron, and thus introduces that 
metal into the solution, it is better not to employ it. After the 
solution is decanted off, an additional dose of nitric acid is to 
be poured upon the residue, and the digestion renewed till a 
complete solution is obtained. The green solutions are now 
neutralized with carbonate of potash, and filtered. By this 
means most of the arseniate of iron separates as a white flocky 
precipitate. 
Separation of a Part of the Arsenic. 
The neutral solution is mixed with acetate of lead as long as 
any precipitate continues to fall, and the mixture is left standing 
for 24 hours in a warm place. The arseniate (and muriate) of 
lead falls to the bottom. In the heat, the acetic acid separates, 
and flies off, frequently with oxide of iron. 
By this means the greater part, but by no means the whole, of 
the arsenic is separated. If the liquid after becoming clear is 
still rendered ae by the solution of lead, a copious additional 
quantity of that solution is poured in, in order to remove the 
arsenic still more completely, and the mixture is allowed to 
remain till the whole of the precipitate collects at the bottom. 
The clear liquid is then drawn off, and the thick portion thrown 
on the filter. As there is usually an excess of lead in the liquid, 
I pour into it a portion of sulphuric acid, and separate the sul- 
phate of lead formed by means of the filter. 
Complete Separation of the Arsenic. 
All the methods hitherto tried by me for separating the arse- 
nic are only incomplete. But the following method seems to 
effect a complete separation. 
I take a quantity of dry sulphuret of barytes still mixed with 
charcoal just as it is after its formation, by heating to redness 
sulphate of barytes and charcoal in a crucible, and put a portion 
of it, about as much as a couple of test-glasses will hold, into 
a large glass vessel. I then add a little water and as much 
diluted sulphuric acid as is just sufficient to neutralize the 
barytes. ‘This is easily found by a few trials. 
nto this mixture | pour with rapidity, before the sulphuretted 
hydrogen has had time to make its escape, the green solution 
not yet quite free from arsenic, and stir the whole about with 
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