Scientific American Supplement, No. 455, September 20, 1884 | Page 6

of arsenite converted into the
aceto-arsenite; and perfect conversion is necessary, as the presence of a
very minute quantity of unchanged arsenite lowers very much the price
of the emerald pigment, and a by no means large quantity renders the
pigment unsalable, owing to its dirty yellowish-green color. 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}.
It is at once seen that I have got the requisite quantity of acetate formed.

I next dissolve the requisite quantity of arsenious anhydride in an
amount of carbonate of soda rather less than is sufficient to neutralize
the acid in the remaining cupric sulphate, and I then bring the solution
to or near 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 fully heated, a small current of it is
allowed to flow into the vat containing the copper salts, and brisk
stirring is kept up in the vat. The 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 he formed in one or two hours, without containing
the slightest trace 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.
Two 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 liquid. To prevent to a certain
extent this loss I precipitated the copper from it as arsenite; but I was
not successful in the few experiments I had time to make on this part of
the subject of reconverting the copper arsenite thus obtained into the
aceto-arsenite by the addition of acetic acid.--Jour. of Science.
* * * * *

ANALYSIS OF ZINC ASH AND CALCINED PYRITES BY MEANS OF

AMMONIUM CARBONATE.
In a recent issue of the Chemiker Zeitung Dr. Kosmann has reported
an analytical method for the examination of zinciferous products;
according to this report, the ash and flue dust produced by the
extraction of zinc from its ore comprise:
1. Zinc dust, from the distillation of zinc,
2. Flue dust, condensed in chambers of zinc furnaces with Kleemann's
receivers,
3. Zinc ash, of various assortments, from iron blast furnaces.
Of these, zinc dust is the only ready product which is, as color or
reducing agent, employed in analytical and technical processes. Its
value, when serving the latter purpose, is determined by the percentage
of finely divided metallic zinc and cadmium contained therein; of equal
reducing power is cadmium, generally associating zinc; injurious, and
therefore uneffective, are