Such a substance can only be sulphide of antimony. With regard to (2), bismuth would act similarly, but under the circumstances could not be present, for the sulphide of bismuth is insoluble in sodic sulphide.
§ 764. Quantitative Estimation.—The quantitative estimation of antimony is best made by some volumetric process, e.g., the sulphide can be dissolved in HCl, some tartrate of soda added, and then carbonate of soda to weak alkaline reaction. The strength of the solution of tartarised antimony thus obtained can now be estimated by a decinormal solution of iodine, the end reaction being indicated by the previous addition of a little starch solution, or by a solution of permanganate of potash, either of which should be standardised by the aid of a solution of tartar emetic of known strength.
3. CADMIUM.
§ 765. Cadmium, Cd = 112; specific gravity, 8·6 to 8·69; fusing-point, 227·8° (442° F.); boiling-point, 860° (1580° F.).—Cadmium in analysis is seldom separated as a metal, but is estimated either as oxide or sulphide.
§ 766. Cadmium Oxide, CdO = 128—cadmium, 87·5 per cent.; oxygen, 12·5 per cent.—is a yellowish or reddish-brown powder, non-volatile even at a white heat; insoluble in water, but dissolving in acids. Ignited on charcoal, it is reduced to metal, which volatilises, and is then deposited again as oxide, giving to the coal a distinct coat of an orange-yellow colour in very thin layers; in thicker layers, brown.
§ 767. Cadmium Sulphide, CdS = 144—Cd, 77·7 per cent.; S, 22·3 per cent.—known as a mineral termed Greenockite. When prepared in the wet way, it is a lemon-yellow powder, which cannot be ignited in hydrogen without loss, and is insoluble in water, dilute acids, alkalies, alkaline sulphides, sulphate of soda, and cyanide of potassium. The solution must not contain too much hydrochloric acid, for the sulphide is readily soluble with separation of sulphur in concentrated hydrochloric acid. It may be dried in the ordinary way at 100° without suffering any decomposition.
§ 768. Medicinal Preparations.—The Iodide of Cadmium (CdI2) occurs in white, flat, micaceous crystals, melting at about 215·5° (419·9° F.), and at a dull red heat giving off violet vapour. In solution, the salt gives the reactions of iodine and cadmium. The ointment of iodide of cadmium (Unguentum cadmii iodidi) contains the iodide in the proportion of 62 grains to the ounce, or 14 per cent.
Cadmium Sulphate is officinal in the Belgian, Portuguese, and French pharmacopœias.
§ 769. Cadmium in the Arts, &c.—Cadmium is used in various alloys. The sulphide is found as a colouring ingredient in certain toilet soaps, and it is much valued by artists as a pigment. The iodide of cadmium is employed in photography, and an amalgam of metallic cadmium to some extent in dentistry.
§ 770. Fatal Dose of Cadmium.—Although no deaths from the use of cadmium appear to have as yet occurred, its use in photography, &c., may lead to accidents. There can be no question about the poisonous action of cadmium, for Marmé,[819] in his experiments on it with animals, observed giddiness, vomiting, syncope, difficulty in respiration, loss of consciousness, and cramps. The amount necessary to destroy life can only be gathered from the experiments on animals. A strong hound died after the injection of ·03 grm. (·462 grain) subcutaneously of a salt of cadmium; rabbits are poisoned if from 19·4 to 38·8 mgrms. (·3 to ·6 grain) are introduced into the stomach. A watery solution of ·5 grm. (7·5 grains) of the bromide administered to a pigeon caused instant death, without convulsion; the same dose of the chloride killed a second pigeon in six minutes; ·25 grm. (3·85 grains) of sulphite of cadmium administered to a pigeon excited vomiting, and after two hours diarrhœa; it died in eight days. Another pigeon died from a similar dose in fourteen days, and cadmium, on analysis, was separated from the liver. From the above cases it would seem probable that 4 grms. (61·7 grains) would be a dangerous dose of a soluble salt of cadmium for an adult, and that in a case of chronic poisoning it would most probably be found in the liver.