Cadmium

CADMIUM, Cadmium, a chemical element, symbol Cd, atomic weight 112.41, atomic number 48. It is contained in small quantities in most zinc ores and is obtained as a by-product during zinc extraction; it can also be obtained electrolytically from solutions of ZnSO₄ containing cadmium. It is a white, lustrous metal, specific gravity 8.6–8.7, harder than tin but cuttable with a knife, and melts at 320.9^o. It does not change in dry air, but in moist air it is covered with a very thin layer of basic cadmium carbonate. It dissolves more slowly in HCl and diluted H₂SO₄ than zinc; in nitric acid it dissolves easily with the formation of nitrogen oxides. In its compounds, cadmium is divalent. Its soluble compounds are poisonous. By its physical, chemical, and pharmacological properties, cadmium belongs to the group of heavy metals, having the most resemblance to zinc and mercury. In medicine, its salts are used. Locally, they precipitate proteins (which form with cadmium compounds soluble in excess NaCl) as well as certain lipoids, e.g., lecithins. The local action manifests as irritation and hyperemia, but in weak solutions cadmium has an astringent action. Its bactericidal properties are not very great, since only a 2% solution of cadmium salts inhibits the growth or kills bacteria; protozoa are more sensitive to it and die in a 1:300,000 solution. In experiments on animals (dogs, rabbits, mice), cadmium salts (e.g., CdCl₂) proved to be only slightly toxic when given per os; for example, in dogs, the introduction of 1.0 pro die for 14 consecutive days caused only a slight decrease in body weight. The sensitivity of frogs to cadmium salts is apparently significantly higher. Acute poisoning in warm-blooded animals is manifested by vomiting, diarrhea, gastroenteritis (tenesmus, discharge of pus and mucus), signs of kidney irritation; further noted is excitation of the central nervous system (clonic convulsions) ending in paralysis, preceded by loss of consciousness. Death results from cessation of respiration. Its action on the cardiovascular system is not severe. At autopsy, degenerative changes are found in the parenchyma of the kidneys, severe hyperemia and hemorrhages in all abdominal organs, especially in the intestines and genital organs. Soluble cadmium compounds (sulfates, carbonates, cadmium oxide), introduced daily into the bodies of animals in small quantities, cause chronic poisoning, according to data from several authors, expressed in severe emaciation, decrease in hemoglobin, fatty degeneration of the liver and cardiac muscle, inflammation of the kidneys; in cats, increased secretion in the upper respiratory passages and in the conjunctiva was also observed. In general, cadmium, by its action on the organism, resembles mercury to some extent and zinc to another; its toxicity is 2–3 times stronger than that of zinc. Cadmium salts are used clinically locally (astringent and antiseptic action), and in recent times also for their resorptive action. Like salts of other heavy metals (Hg, Bi, Au, etc.), cadmium salts have been proposed for the treatment of syphilis. Their activity proved to be lower than that of mercury and bismuth salts, but in combination with salvarsan they give an extremely strong effect. Attempts have also been made to treat other protozoan diseases (e.g., malaria) with cadmium salts, but with less success. In technology, cadmium salts find wide application in photography, dyeing, etc. Crystals of cadmium sulfate are part of the Weston element (see Weston normal element). Low-melting alloys of metallic cadmium with bismuth, with tin, or with tin and bismuth are used in dental practice (cadmium amalgam); cadmium is part of the Wood's alloy. 1. Cadmium subsalicylate [C_eH₄(OH)COO]₂Cd—colorless crystals of very weakly acidic or neutral reaction, soluble in 68 parts of cold water and in 24 parts of hot water, in alcohol, ether, and in warm glycerin. It has been proposed (but little used) externally in the form of eye ointments (0.1:10.0) and eye lotions (0.2:12.0) for purulent ophthalmitis, corneal inflammation, and conjunctivitis, in a 1:1,000 solution for douching in gonorrhea and vaginitis. 2. Cadmium sulfate (3CdSO₄-r-8H₂O)—colorless, transparent crystals, efflorescent in air, with a bitter taste, soluble in two parts of water, insoluble in alcohol. Aqueous solutions have a weakly acidic reaction. Externally—as an astringent in ophthalmic practice (especially in conjunctivitis catarrhalis) in aqueous solution (0.05–0.2:10.0) and in ointments «3 (0.1–0.2:10.0 of fat), as well as for douching in gonorrhea and otorrhea (1% aqueous solution). Internally in pills (0.005–0.01 each) for syphilis and rheumatism (little used). 3. Cadmiol (10% oily suspension of Cadmii subsalicylici), proposed in recent times for the treatment of syphilis; it is injected intramuscularly 0.5–1.0 cm³ twice a week; some authors have seen good success. It has also been used against various forms of malaria (Reitler), but without a marked effect; it is also proposed to combine its use with quinine to enhance the latter's action.

M. Nikolaev. Detection in judicial cases and in professional poisonings. For the detection of cadmium (e.g., in vomit, urine, etc.), organic substances are destroyed (see Poisons—isolation) and cadmium is precipitated as yellow cadmium sulfide, insoluble in aqueous ammonia and ammonium polysulfide. Cadmium sulfide is dissolved in nitric acid (concentrated, diluted with an equal volume of water), the solution is evaporated, and the residue is dissolved in water. In the resulting solution, aqueous ammonia gives a white precipitate, soluble without coloration in excess of reagent. When heating cadmium compounds with carbon, the reducing metallic cadmium relatively easily volatilizes. For the detection of cadmium vapors (its oxide) in air, a definite volume of the latter is drawn through flasks with nitric acid by means of an aspirator (see Poisons—isolation). The liquid is evaporated, and cadmium is detected as described above. For quantitative determination, the obtained cadmium sulfide is placed in a flask with a ground glass stopper, a definite volume of titrated iodine solution (e.g., ^p/₁₀₀) is added, concentrated HCl is added, and after 15 minutes the excess iodine is back-titrated with thiosulfite.

A. Stepanov. Cadmium as an industrial poison and the pathologic changes of professional character caused by it are not yet fully accurately studied, since in most cases of poisoning the action of lead, zinc, and arsenic cannot be excluded. Cadmium sulfide is used as a pigment (yellow color); cadmium is part of low-melting alloys (e.g., Wood's metal). Cadmium and its compounds are used in chemical and physical laboratories, in photography (when photographing in ultraviolet light of a certain wavelength in an electric arc, a certain amount of cadmium vapors is formed). Cases of professional cadmium poisoning have been described a few times, and everywhere the cause of poisoning was the inhalation of cadmium vapors. In Saxony in 1914, there was a poisoning of a worker engaged in the melting of cadmium plates for electric mine lamps. Legge described three cases of poisoning of persons working during the melting of cadmium (one of which ended fatally). Symptoms: headache, vomiting, chills, tachycardia. At autopsy, the following were found: hyperemia of the mucous membranes of the respiratory tract, inflammation of the kidneys, stomach, and intestines, fatty degeneration of the liver and cardiac muscle. Stephens (1920) at autopsy of persons working during the melting of zinc in Wales found zinc and cadmium in their livers. Among zinc smelters, he notes many cases of poisoning in which the symptoms very closely resemble the picture of cadmium poisoning: pressure and pain in the stomach area, nausea, diarrhea and constipation, loss of appetite, thirst, unpleasant taste in the mouth. Workers are poisoned mainly those engaged in the initial smelting of zinc; here the mineral galmei, which contains 0.5–1.5% cadmium, is used in the process; the latter, being a more fusible metal, gives off vapors into the air first. During cadmium mining in Germany, several cases of poisoning by arsine were observed. Preventive measures are the same as with zinc work: hermetic sealing of apparatus and powerful exhaust ventilation.