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 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.”