126 
Brass . 
place of it, employs sulphuric acid, which is much cheap- 
er. His process, which has fully answered his expecta- 
tion, is as follows : 
The proportion of silver in the alloy is first to be ascer- 
tained by the touch, or in any other way. For each part 
of silve' one part of sulphuric acid, and for each part of 
copper three and three-fifth parts of the same acid, are to 
be taken. The acid, diluted with half its weight of water, 
is to be poured into the matrass on the alloy, reduced to 
small pieces. An addition of one part more of the acid 
to every sixteen parts of the alloy facilitates the solution. 
Place the matrass in a sand heat, and bring the contents 
to a state of ebullition. If care be taken to stir it frequently 
with a glass rod, the alloy will be broken down and con- 
verted into a sulphat in two or three hours. It will be- 
come thick, and sometimes hard. While still hot, six or 
eight times its weight of boiling water is to be added to it, 
and the heat to be continued for some time. By this 
means the sulphat will be dissolved, and a great part of 
the sulphat of silver will be precipitated. When the whole 
is found to be completely dissolved, a clean plate of cop- 
per, or a few pieces of clean copper money tied loosely 
in a coarse cloth, is suspended in the^fluid, and the boiling 
is continued for some hours, by which means all the sul- 
phat of silver is decomposed, and the metal separated in a 
metallic form. 
To ascertain when the separation is complete, a small 
quantity of the solution is taken out and tried, by adding 
a few drops of a solution of muriat of soda. If a curdly 
precipitate is formed, it is a proof that some of the silver 
still remains in it in which case the boiling must be con- 
tinued. 
When a complete separation is effected, the clear so- 
lution is to be decanted off* with care, and the precipitate 
washed. To ascertain that all adhering sulphat of copper 
