In cold weather a
much longer time is required for its complete conversion; even at the end
of a fortnight or three weeks there frequently remains sufficient
unconverted arsenite to affect seriously the selling price of the color;
when this occurs the manufacturer generally removes these last traces by a
most wasteful method viz, by adding a quantity of free sulphuric acid. The
acid of course dissolves the arsenite, but it dissolves in very much
larger quantities the aceto-arsenite; and this costly solution is not
utilized, but is run into the factory sewer.
By my method of manufacturing it, it can be produced in winter as well as
in summer in one or two hours, and the quantity of free acid required for
its formation is reduced to the lowest amount. I proceed as follows: After
having dissolved in hot water the requisite quantity of cupric sulphate, I
decompose one-fourth of this salt by adding just sufficient of a solution
of carbonate of soda to precipitate the copper, in that quantity of the
sulphate, as carbonate. I then add just sufficient acetic acid to convert
the carbonate into acetate. I have now got in solution--
3CuSO_{4} + Cu(C_{2}H_{3}O_{2})_{2},
and I have to transform it into--
3CuAs_{2}O_{4} + Cu(C_{2}H_{3}O_{2})_{2}.
Pages:
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31