Manufacturer and builder 1, 1869
The compounds of the metal chromium are among the most useful and most common of the substances used in the manufacture of paints. The colors made from it range from green, through all shades of yellow and orange, to red, and are all, with hardly an exception, bright and beautiful. For that reason they have superseded many paints formerly used - such, for instance, as orpiment, massicot, and others.
Chromium was only discovered at the end of the last century, and the name given to it - derived from the Greek - was chosen on account of the many colors that can be produced from it. It was a mere curiosity at first, until, in Maryland, extensive deposits were found in combination with iron ore. This compound is analogous to magnetic iron ore, which consists of a combination of sesquioxide of chromium and oxide of iron. This substance is that from which all preparations of chromium are derived. It is converted into a chromate of potassa in the following manner:
The ore, having been reduced to powder, is calcined with nitre, or with carbonate of potassa, quicklime being sometimes added, and heated for a long time in a reverberatory furnace. The product is treated with water, and a yellow solution obtained, which upon evaporation deposits lemon-yellow crystals of chromate of potassa. These crystals are a combination of potassa with an acid formed by the chromium, and called chromic acid. This acid is similar to sulphuric acid, and it forms, with the potassa, the above-named chromate of potassa. When a small quantity of sulphuric acid is added to this salt, half the potassa is removed, combining with this acid, and the remaining half of the potassa combines with double the quantity of chromic acid, and thus is the so-called neutral chromate of potassa converted into a bichromate of potassa. Of this salt immense quantities are manufactured for use in the arts. It forms beautiful red crystals. Dissolved in water, it forms, according to the amount dissolved, yellow, orange, or red solutions. One part will saturate ten parts of water. The solution has acid properties, and is quite poisonous.
In order, now, to make chrome-yellow, all that is necessary to be done is to make a solution of some lead salt, as, for instance, the acetate of lead, or, in other words, the sugar of lead, or the nitrate of lead. When such a solution is mixed with a solution of the chromate or bichromate of potassa , a yellow or orange precipitate of chromate of lead will be formed, of which the shade will be regulated by observing certain particulars which will be hereafter explained. The precipitate, dried and boxed up for the trade, is manufacture in this country upon a very large scale, and is known in Europe as American chrome-yellow. Unlike many other articles, it may also be manufactured to advantage on quite a small scale.