its Properties and Manufacture. 
I ^4d j - rupc-n, ws una manufacture. • 
dissolved in hot water the requisite quantity of cupric 
P f e ’ decompose one-fourth of this salt by adding just 
ufficient of a solution of carbonate of soda to precipitate 
T 1X 1 t ^ 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 — 
3CuS0 4 + Cu(C 2 H 3 0 2 ) 2 , 
and I have to transform it into — 
3CuAs 2 0 4 + Cu(C 2 H 3 0 2 ) 2 . 
It is at once seen that I have got the requisite quantity of 
acetate foimed. I next dissolve the requisite quantity of 
arsemous anhydride in an amount of carbonate of soda 
rather less than is sufficient to neutralise the acid in the re- 
maining cupiic sulphate, and I then bring the solution to or 
neai the boiling-point by introducing steam into it : the 
arsenic is dissolved not in the same vessel as the copper 
salt, but in a separate one. When the arsenic solution is 
lully heated a small current of it is allowed to flow into the 
vat containing the copper salts, and brisk stirring is kept up 
m the vat. I he emerald-green is at once formed; but if 
there should be the slightest formation of any arsenite, the 
flow of the arsenic solution is at once stopped until every 
trace of the arsenite has been converted: the arsenic solution 
is then allowed to flow in again, with the same precautions 
as before : in this way a large batch of emerald-green can 
be formed in one or two hours, without containing the 
slightest tiace of the arsenite. I keep the arsenic solution 
near the boiling-point during the whole of the time it is 
flowing into the other vessel. By varying the proportions 
of water I could either make it coarse or fine, as I wished 
which is an important matter to have complete control over 
in its manufacture. 
Iwo points of interest occurred to me during the time I 
was occupied with the research, which I had not time to 
complete : one was whether the aceto-arsenite can be formed 
adopting the old method for its formation, if there is more 
than a. certain quantity of water ; from some experiments I 
made in this direction I was inclined to the opinion it could 
not. I have already stated that emerald-green is soluble to 
a certain extent in acids, and that it is formed in a more or 
less acid solution ; consequently a varying amount of the 
pigment is always lost by being dissolved in the supernatant 
