as described by Dr. Ehrmann in the "Ann. Pharm.,"
xii., 92, is given. It is thus stated in Wagner's work: "This pigment is
prepared by first separately dissolving equal parts by weight of arsenious
acid and neutral acetate of copper in boiling water, and next mixing these
solutions while boiling. There is immediately formed a flocculent
olive-green colored precipitate of arsenite of copper, while the
supernatant liquid contains free acetic acid. After a while the
precipitate becomes gradually crystalline, at the same time forming a
beautiful green pigment, which is separated from the liquid by filtration,
and after washing and carefully drying is ready for use. The mode of
preparing this pigment on a large scale was originally devised by M.
Braconnot, as follows: 15 kilos. of sulphate of copper are dissolved in
the smallest quantity of boiling water, and mixed with a boiling and
concentrated solution of arsenite of soda or potassa, so prepared as to
contain 20 kilos. of arsenious acid. There is immediately formed a dirty
greenish-colored precipitate which is converted into Schweinfurt green by
the addition of some 15 liters of concentrated wood-vinegar. This having
been done, the precipitate is immediately filtered off and washed."

As I have already stated, the copper salt used in the manufacture of this
pigment in England is the sulphate, and it is carried out pretty much
according to Braconnot's method as described by Dr Ehrmann; but any one
would infer, from reading his description of the manufacturing process,
that the compound, aceto-arsenite of copper, was formed almost immediately
after the addition of the acetic acid, a higher or lower atmospheric
temperature having no effect in hastening or retarding the formation.
Furthermore, it is not stated whether the compound forms more readily in
an acid or neutral solution, or whether it can or cannot be formed in a
neutral one; now both these points are important to notice in describing
its manufacture. As regards the former I shall notice it presently, and,
as far as my knowledge extends, the pigment will not form when the
solution is neutral.

The operation is conducted in the following manner in the factory: The
requisite quantity of sulphate of copper is placed in a large wooden vat,
and hot water added to dissolve it; the requisite quantity of arsenic
(arsenious anhydride) and carbonate of soda, the latter not in quantity
quite sufficient to neutralize the whole