Elements of the Theory and Practice of Chymistry, 5th ed.

by Pierre Joseph Macquer

Though the Copper melts in this operation, yet it is far from being necessary to apply such a strong fire as Copper usually requires to melt it: for the accession of the Zinc, on this occasion, communicates to it a great deal of fusibility. The increase of its weight is also owing to the quantity of Zinc combined with it. Copper acquires still another advantage by its association with this semi-metal; for it remains longer in the fire without calcining.

Brass well prepared ought to be malleable when cold. But in whatever manner it be made, and whatever proportion of Zinc there be in it, it is constantly found quite unmalleable when red-hot.

Brass melted in a crucible, with a fierce heat, takes fire almost like Zinc, and from its surface many white flowers ascend, dancing about in flakes like the flowers of Zinc. They are indeed the flowers of Zinc, and the flame of Brass urged by a strong fire is no other than the flame of the Zinc that is united with the Copper, and at that time burns. If Brass be thus kept long in fusion it will lose almost all the Zinc it contains. It will also lose much of its weight, and its colour will be nearly that of Copper. It is therefore necessary, towards performing this operation aright, to seize the moment when the Copper is sufficiently impregnated with Zinc, when it hath acquired the most weight and the finest colour, with the least detriment to its ductility, that is possible, and that instant to put out the fire; because, if the Copper be left longer in fusion, it will only lose the Zinc already united with it. Skill acquired by much practice, and an acquaintance with the particular Calamine employed, are necessary to guide the artist surely through this operation; for there are very considerable differences between the sundry ores of Zinc. Some of them contain Lead, as was said above, and in others there is Iron. When these heterogeneous metals come to be mixed with the Copper, they do indeed augment its weight, but they render it at the same time pale, and make it very harsh. Some Calamines require to be roasted before they can be used for this purpose, and in the torrefaction emit vapours of a Volatile Alkali, succeeded by vapours of a Sulphureous Spirit: others exhale no vapours while roasting, and may be employed without any antecedent preparation. These different qualities must evidently produce great differences in the operation.

Brass may also be made as Prince's metal and other imitations of Gold are actually made, by using Zinc in substance, instead of the ores that contain it. But these compositions have not, when cold, the ductility of Brass prepared with Lapis Calaminaris, because Zinc is seldom pure, or free from a mixture of Lead. Perhaps also the different manner in which the Zinc unites with the Copper may contribute to this variation.

To obviate this inconvenience, the Zinc must be refined from all alloy of Lead. The property of being indissoluble by Sulphur, which this semi-metal possesses, points out a very practicable method of doing it. The Zinc must be melted in a crucible, and stirred briskly with a strong iron wire, while tallow and mineral Sulphur are alternately projected upon it; but so that the quantity of Sulphur may greatly exceed that of the tallow. If the Sulphur do not burn entirely away, but form a kind of scoria on the surface of the Zinc, it is a sign that your semi-metal contains Lead. In this case you must continue throwing in more Sulphur, and keep stirring the Zinc incessantly, till you perceive that the Sulphur ceases to unite any more with a metallic substance, but burns freely on the surface of the Zinc. The semi-metal is then refined, because the Sulphur, which cannot dissolve it, unites very readily with the Lead, or other metallic substance, contained in it.

If Zinc thus refined be mixed with pure Copper, in the proportion of a fourth or a third part, and the mixture be kept in fusion and constantly stirring for some time, the Brass produced will be as ductile, when cold, as that made by cementation with the Lapis Calaminaris.

With regard to Prince's metal, and other imitations of Gold, they are made either with Copper or Brass re-combined with more Zinc. As it is necessary, for giving them a fine golden colour, to mix with them other proportions of Zinc than that acquired to make Brass only, they are generally much less ductile. In 1725, M. Geoffroy gave a Memoir on this subject in which he examined the effects of incorporating both Copper and Brass with Zinc, from a small to a very large quantity.

PROCESS IV.

Zinc dissolved in the Mineral Acids.

Weaken concentrated Oil of Vitriol by mixing with it an equal quantity of water. Into a matrass put the Zinc you intend to dissolve, first broken to small pieces. Pour on it six times its weight of the Vitriolic Acid, lowered as above directed, and set the matrass in a sand-bath gently heated. The Zinc will dissolve entirely, without any sediment. The Neutral Metallic Salt resulting from this dissolution shoots into crystals, which go by the name of White Vitriol, or Vitriol of Zinc.