Manufacturer and builder, 1870 (page 271)
Blue or copper vitriol is the crystallized sulphate of copper, and contains, when pure, 31.85 oxide of copper, (25.4 copper,) 32.07 sulphuric acid, and 36.08 water.
Formerly the so-salled mixed vitriols, (Salzburg, Cyprian, Eagle vitriols, etc.,) containing a greatly varying percentage of copper, and a greater or less admixture of the sulphates of zinc, iron, etc., were extensively manufactured in connection with the mining of poor copper ores. They were then much used in the arts and manufactures; but as a certain percentage of copper in the vitriol is often required, most establishments prefer at present to buy the pure vitriols and prepare their mixtures themselves. For this reason the production of mixed vitriols has fallen off considerably, and the manufacture of the pure article has increased in all parts of the world. In this country, the manufacture of copper vitriol, as a regular business, is comparatively recent, and has assumed its greatest proportions since last year, when Congress imposed an exceedingly heavy tariff on the imported. article. We do not propose to go into details in regard to all the different methods proposed and carried out in divers parts of the world, as the number of these processes is altogether too large to permit discussion in the columns of this paper. We intend to describe only the methods best suited to the circumstances surrounding any manufacture in this country, that is, such as are simplest in execution and the cheapest. The consumption of blue.vitriol in this country is at present very large, and is steadily increasing. It is used principally in dyeing and printing; for the manufacture of green and blue colors; in telegraphy; for the conservation of grain, wood, and skins. Of less importance is its use in galvanoplastic; as a medicine in laboratories; for the preparation of absolute alcohol; for the manufacture of the so-called copper soap, (the green precipitate resulting from the mixture of a solution of sulphate of copper with a soap-solution, and used as an oil-color,) and for the bronzing of plaster statues.
It is manufactured in its purest state from metallic copper and sulphuric acid, the acid being used in some establishments concentrated, in others diluted with water. In the former process, much residuum of a mixture of sulphide of copper and oxide of copper is formed during the dissolving process, and this is lost for the final product of the particular campaign in which it is produced, while at the same time considerable sulphuric acid is lost as sulphurous acid; the latter, or diluted acid process, is therefore the cheaper of the two, and especially appropriate in connection with sulphuric acid works, where the chamber-acid from the first chamber can be directly used. The manner of proceeding is the following:
The copper is thrown into the dissolving-vessels in the shape of granules, chips, in short, in as small pieces as possible, and in such quantity as to fill a little over half of the tubs. Sprinkled with hot diluted sulphuric acid under access of the air, the metal will dissolve, and sulphate of copper will be formed. The heating of the acid is effected by steam in wooden, lead-lined vessels, and from these the acid is conducted over the copper by means of pipes and rose-heads in thin streams. The dissolving vessels have double bottoms, the upper one being perforated. The acid, percolating through the copper, dissolves it; a very concentrated solution is formed—in fact, so concentrated that, in the troughs below the vessels, crystals of vitriol are deposited along the bottom as soon as the lye begins to cool. The acid mother-liquor runs into a vessel at the end of the troughs, from which it is raised by steam, pressing on top of the liquor, or by other convenient contrivances, into the vessel above holding the hot sulphuric acid. It is then used over again for dissolving new quantities of copper. The crystals are taken out of the troughs and deposited on platforms in front of the troughs, and inclined toward them. Here they are washed with cold water, in order to remove the adhering acid mother-liquor, then transferred to wooden, lead-lined vessels, where they are dissolved in hot water, of which as little as possible is used, in order to produce a concentrated solution, out of which the vitriol will quickly crystallize. The liquid, after standing for some time, is drawn off by means of siphons from the residuum, (which is alwayi present in small quantity,) and conducted into crystallization-vats of square form. Strips of lead hang down into these vats from sticks laid across their top; and on these are deposited the largest and most beautiful crystals. The crystals are the larger the greater the surface of the vitriol solution exposed. Around the leaden sides and the bottom of the vats is collected a dense mass of smaller crystals, which in many establishments form an article of secondary value, and one kept separate, not on account of their constituents, but simply because their appearance is not so inviting. In other works, tine smaller crystals are dissolved again and recrystallized. In most factories, however, all the vitriol formed is taken out after a fortnight, spread on inclined platforms, and washed; or else this operation is performed in baskets, perforated boxes, and the like, which are moved to and fro in vats containing cold water. The mother-liquor and wash-water are both conducted into vessels, from which they are raised into the hot-water tanks above, to be used again for dissolving vitriol. The washed article is thrown upon broad, inclined platforms, in order to let the water run off, and is then dried on drying-scaffolds ley artificial heat. It is packed in wooden barrels, and can thus be shipped without danger of injury.
In our next we shall speak of the manufacture of sulphate of copper from sulphurets of copper, both the natural and the artificially prepared.