re I never heard that any of the factory hands
suffered, nor did I suffer, from arsenical poisoning. If there is any
abrasion of the skin the dust produces a sore, and also the delicate
lining of the nostrils is apt to be affected. It is in this way it acts in
large doses; I am therefore very skeptical as to its supposed poisonous
effects when wall-paper is stained with it.

Different methods are given in works on chemistry for the manufacture of
this pigment, but as they do not agree in every respect with the method
which was followed in English color factories some years ago, it will be
as well, for the full elucidation of the manufacture of this substance, to
briefly recite some of these methods before describing the one that was,
and probably is still, in use; and I will afterward describe a method
which I invented, and which is practically superior to any other, both in
the rapidity with which the color can be formed, and for producing it at a
less cost.

It is stated in Watts' "Dictionary of Chemistry" that it is "prepared on a
large scale by mixing arsenious acid with cupric acetate and water. Five
parts of verdigris are made up to a thin paste, and added to a boiling
solution of 4 parts or rather more of arsenious acid in 50 parts of water.
The boiling must be well kept up, otherwise the precipitate assumes a
yellow-green color, from the formation of copper arsenite; in that case
acetic acid must be added, and the boiling continued a few minutes longer.
The precipitate then becomes crystalline, and acquires the fine green
color peculiar to the aceto-arsenite." I do not know from personal
knowledge, but I have always understood that the copper salt employed in
its manufacture in France is the acetate. This would account, in my
opinion, for the larger crystalline flakes in which it is obtained in
France than can be produced by the English method of manufacturing it.
Cupric acetate is never employed, I believe, in England--the much cheaper
copper salt, the sulphate, being always employed.

In "Miller's Chemistry" it is stated it "may be obtained by _boiling_
solutions of arsenious anhydride and cupric acetate, and adding to the
mixture an equal bulk of _cold_ water." Why it should be recommended to
add _cold water_, I am at a loss to understand.

In Drs. Roscoe and Schorlemmer's large work on "Chemistry," and in the
English edition of "Wagner's Handbook of Chemical Technology," edited by
Mr. Crookes, the process