Green substances, so carefully treated that they only contain phyllocyanate of copper, would yield but small quantities of copper, and probably they would not be injurious to health; but the coppering is usually more extensive, and copper leguminate and other compounds are formed; for the vegetables, when exhausted by alcohol, give a residue which, successively exhausted by water, by soda-lye, and lastly by hydrochloric acid, parts with copper into the three solvents mentioned.
It might be argued that, from the insoluble character of the phyllocyanate of copper, and especially seeing that it does not dissolve in strong hydrochloric acid, that it would be perfectly innocuous; but Tschirch has proved that, whether the tartrate of copper (dissolving easily in water), or copper oxide (not dissolving at all in water, but soluble in hydrochloric acid), or phyllocyanate of copper (insoluble both in water and in hydrochloric acid) be used, the physiological effect is the same.
Copper may be found in spirits, owing to the use of copper condensers, a remark which applies also to the essential oils, such as oleum cajepute, menthæ, &c.[870] In France, it has been added fraudulently to absinthe, to improve its colour.[871] Green sweetmeats, green toys, green papers, have all been found to contain definite compounds of copper to a dangerous extent.
[870] According to Eulenberg (Gewerbe Hygiene, p. 716), Oleum cajepute, Menth. pip., Melissæ, Tanaceti, &c., are almost always contaminated with copper.
[871] Tardieu, Étude Méd. Lég. sur l’Empoisonnement.
§ 801. Preparations of Copper used in Medicine and the Arts.
(1) Medicinal Preparations:—
Sulphate of Copper, Cupri Sulphas, CuSO45H2O.—This well-known salt is soluble in water at ordinary temperature, 3 parts of water dissolving 1 of the sulphate; but boiling water dissolves double its weight; 1 part of copper sulphate dissolves in 21⁄2 of glycerin; it reddens litmus, and is slightly efflorescent; its solution responds to all the usual tests for copper and sulphuric acid. A watery solution of the salt to which twice its volume of a solution of chlorine has been added, gives, when treated with ammonia in excess, a clear sapphire-blue solution, leaving nothing undissolved, and thus showing the absence of iron. Besides iron, sulphate of copper has been found to contain zincic sulphate.