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 of the sulphuric acid set free from the sulphate of copper on the precipitation of the copper as arsenite, are placed in another wooden vessel; water is then added, and the formation of the arsenite of soda and its solution are aided by the introduction of steam into the liquid. When complete solution has been effected the arsenic solution is run off into the vat containing the solution of the sulphate of copper, arsenite of copper being at once precipitated. The necessary quantity of acetic acid is afterward added. In warm weather the formation of the aceto-arsenite soon commences after the addition of the vinegar; but, even in that case, it takes a week or more to have the whole of a big batch 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—

and I have to transform it into—

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.

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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 zinc oxide and oxides of other metals, also metallic lead.

Flue dust, condensed in chambers of zinc furnaces with Kleemann's receivers, is employed with zinc ores in the extraction of zinc, and in small quantities as substitute for zinc white; its commercial value is similarly estimated as that of zinc ores.

The various modifications of zinciferous flue ashes from blast furnaces are an object for continual demand, being both a