Paints made of Copper. Ferrocyanide of Copper.

Manufacturer and builder 10, 1870

This is a comparatively new pigment, and as yet has received no name for common use. We are, therefore, under the necessity of designating it by its scientific name, which, at the same time, reveals its chemical composition.

In the same way as the four so-called elementary halogens — chlorine, bromine, iodine, and fluorine — combine with metals and form compounds, some of which are pigments, the compound halogens — cyanogen, ferrocyanogen, ferridcyanogen, sulphocyanogen, etc. — combine with metals, and some of their compounds are likewise pigments. Thus, the combination of iron with the compound halogen ferrocyanogen, forms Prussian blue, and the combination of copper with the same ferrocyanogen forms the red pigment now in question.

To understand the nature of this ferrocyanogen we must first recall that cyanogen is a compound of nitrogen and carbon, 14 parts of nitrogen, by weight, being combined with 12 of carbon. But, since the symbol of nitrogen, N, stands for 14 parts by weight of this substance, and the symbol C, for 6 parta of carbon, (see MANUFACTURER AND BUILDER, VOL. II, page 98,) the cyanogen is expressed by the formula, N C₁. Since this compound, however, behaves, to all intents and purposes, as a single element, a separate symbol, Cy, has been adopted, and may be used as well as N C₂, both meaning the same thing.

This substance will, as already remarked, cmnbine with metals; and it it worthy of notice here that it forms, with gold and silver, soluble salts, from which the most common solutions are made for gilding and silvering by the electro-plating process.

But the most remarkable circumstance is, that when this cyanogen, Cy, or N C₂, (which stands for 26 parts,) combines with 27 parts of iron, which are expressed by the symbol Fe, it forms a new compound. Fe Cy, called ferrocyanogen, which, again, behaves like an elementary substance, and enters into new combinations with metal, forming a new series of compounds called ferrocyanides.

In order to make the ferrocyanide of copper, we take a solution of about 9 parts of the common yellow prussiate of potash, which is a ferrocyanide of potassium, and mix it with a solution of nearly 4 parts of blue vitriol or sulphate of copper. The result is a precipitate which, when washed and dried, possesses a violet-red color of a very pleasing shade; and this, when diluted with white, becomes pink. Although the color of this pigment is not dark, it is highly intense, and will bear a considerable amount of dilution with chalk white, for instance. In this way it can be manufactured into an excellent watercolor, of much purer appearance than can be obtained from the mixture of other pigments.

For the benefit of students in chemistry we append here the formula of its manufacture, somewhat simplified:
Cu O₂ S O₃ + K, F Cy.
Result, K O, S O₃ + Cu F Cy.
Or, sulphate of potash + the new pigment.

This color has never yet been made on a large scale, nor even, up to the present time, introduced to the trade. We think it a valuable one, and, believing its adoption and introduction would be profitable, too recommend it for experiment to those interested.