Sec. LVI. Of Blue Vitriol.
Different preparations of copper are used in fire-works, to communicate colour to the flame; and besides copper filings, brass filings, verdigris, and the oxides of copper, the sulphate of copper, or blue vitriol, has been employed. We may observe here, that there are three sub-species of this salt; the bisulphate, sulphate, and sub-sulphate, the first properly speaking being the blue vitriol of commerce.
The sulphate, although recommended in some of the old formulæ for coloured fire, is not, however, preferable to some other preparations of copper. The use and application of copper, and its preparations, will be seen in the article on coloured fire.
When sulphate of copper is heated, it is converted into a bluish-white powder. If the heat be increased, the acid is expelled, and the black oxide of copper remains. Before it is used, it is exposed to heat to expel the water of crystallization. It ought to be in the state of impalpable powder. It is composed of 33 acid, 32 oxide, and 35 water. It is decomposed by the alkalies and earths, the alkaline carbonates, borates, and phosphates, and several metallic salts.
The oxide may be obtained very readily from this salt, for the purpose of fire-works, by dissolving it in water, and adding a solution of caustic potassa; collecting the precipitate, and drying it in a moderate heat. This will expel the water that may be contained in it; as metallic precipitates, made in this way, are more or less in the state of hydrates.
When metallic copper is required, it may be obtained in fine powder, and very expeditiously, by immersing a plate of iron in a solution of any of the salts of copper, as the sulphate. It will precipitate on the iron, and gradually fall to the bottom of the vessel. This metallic copper will be found to be much more impalpable than the filings, however fine, and, for that reason, may be mixed more accurately with different substances.
Copper burns with a beautiful green flame, and deposites a loose greenish-gray oxide. The ammonia-oxalate of copper, of which there are three sub-species, burns with flame.
Sec. LVII. Of Nitrate of Copper.
This preparation of copper is used in some fire-works. It communicates a green colour to flame. When combined with carbonaceous substances, the combustion is vivid. This is owing to the decomposition of the nitric acid, (in the same manner as the acid of nitrate of potassa and other nitrates is decomposed), during which carbonic acid and deutoxide of azote are produced. Nitrate of copper has been more particularly recommended for the preparation of match stick, similar to that of M. Cadet, and of match rope. It is used in the same manner as the nitrate of lead. M. Proust used it in lieu of nitrate of lead when repeating some experiments of M. Born. It is more expensive than the acetate, or even the nitrate of lead. Its effect, however, is the same.
Nitrate of copper attracts the moisture of the atmosphere, and deliquesces. Acetate of lead, on the contrary, by exposure to the air gradually effloresces, and in time is decomposed. The preparations of lead, for that reason, are preferable to the nitrate of copper.