THALLIUM 547 The liver is congested and shows fatty degeneration. The kidneys are con- gested, the glomeruli are swollen, and cloudy swelling and necrosis of the cells are seen in the convoluted tubules. The trachea and bronchi are congested. The lungs are congested with subpleural haemorrhages. The heart shows fatty degeneration.20 Chemical Analysis.—The detection of thallium in viscera or urine is carried out as follows 21 : — A weighed quantity of the material is broken up with hydrochloric acid and potassium chlorate by Fresenius and Babo method and, when solution of all the material except fat has been achieved, the liquid is filtered (well washing the precipitate), and the filtrate boiled until practically all the excess of chlorine has been driven off or removed by the sulphur dioxide method. If necessary, it is filtered again, discarding the precipitate. To the filtrate ammonium chloride and ammonia are added and it is then boiled. The precipitate which consists of iron, calcium and magnesium chiefly in the form of phosphates, is filtered off and discarded. It may be advisable to add a small amount of calcium chloride solution to the liquid before the ammonia to ensure complete removal of phosphate. The filtrate is then saturated with sulphuretted hydrogen or an excess of freshly prepared ammonium sulphide is added; a black precipitate is then, formed. The precipitate is filtered off, well washed with dilute ammonium sulphide, and finally with distilled water. It consists of thallium sulphide together with traces of other metals which precipitate with sulphuretted hydrogen in an alkaline solution but so far as toxicological analyses are con- cerned, the only likely metal to be present—and then only in traces—is copper. When the precipitate is completely washed it is dissolved off the paper with hot dilute hydrochloric acid. The thallium is converted into thallous chloride and any trace of the copper which was present as the sulphide remains behind, for this sulphide is insoluble in dilute hydrochloric acid. To the solution ammonia is added in slight excess and the liquid is boilefi. If the process of separation has been completed no precipitate should occur at this stage. Any precipitate should be filtered off and discarded. This filtrate is then made very faintly acid, and excess of potas- sium iodide solution is added. An immediate yellow precipitate of thallous iodide forms. As there is some tendency for thallous iodide to come down in colloidal form, the liquid should be boiled and allowed to stand for twelve hours. The precipitate is then collected in a weighed Goodh, crucible and is well washed, first with potassium iodide solution and subsequently with alcohol, until the washings give no reaction for an iodide. The crucible is then dried at 120°C. until constant weight is obtained. Although thallous iodide is very slightly soluble in water (1 : 17,000), it is almost completely insoluble in potassium iodide solution and in alcohol, so that filtration in the cold and washing with these reagents will give an accurate estimate of the amount present. The iodide after weighing may be confirmed as thallium by dissolving it in a solution of sodium thiosulphate, in which it is only dissolved with difficulty, whereas lead iodide is readily soluble. Finally, some of the iodide may be heated in a Bunsen flame on a plati- num wire and the characteristic green line in the spectrum obtained. Medico-Legal Points.—Poisoning by thallium is rare as contrasted with that by lead or mercury, owing probably to the relatively infrequent use of the former in medicine and industry. A few accidental cases of poisoning have occurred from the internal administration of thallium acetate or from 20. Roche Lynch and Scovell, Lancet, Dec. 20, 1930, p. 1342. 21, Ibid., p. 1342.