Читать книгу Poisons, Their Effects and Detection - Alexander Wynter Blyth - Страница 58

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§ 43. Chlorine is a yellow-green gas, which may, by cold and pressure, be condensed into a liquid. Its specific gravity is, as compared with hydrogen, 35·37; as compared with air, 2·45; a litre under standard conditions weighs 3·167 grms. It is soluble in water.

The usual method of preparation is the addition of hydrochloric acid to bleaching powder, which latter substance is hypochlorite of lime mixed with calcic chloride and, it may be, a little caustic lime. Another method is to treat manganese dioxide with hydrochloric acid or to act on manganese dioxide and common salt with sulphuric acid.

Accidents are liable to occur with chlorine gas from its extensive use as a disinfectant and also in its manufacture. In the “Weldon” process of manufacturing bleaching powder, a thick layer of lime is placed on the floor of special chambers; chlorine gas is passed into these chambers for about four days; then the gas is turned off; the unabsorbed gas is drawn off by an exhaust or absorbed by a lime distributor and the doors opened. Two hours afterwards the men go in to pack the powder. The packers, in order to be able to work in the chambers, wear a respirator consisting of about thirty folds of damp flannel; this is tightly bound round the mouth with the nostrils free and resting upon it. The men are obliged to inhale the breath through the flannel and exhale through the nostril, otherwise they would, in technical jargon, be “gassed.” Some also wear goggles to protect their eyes. Notwithstanding these precautions they suffer generally from chest complaints.

§ 44. Effects.—Free chlorine, in the proportion of 0·04 to 0·06 per thousand, taken into the lungs is dangerous to life, since directly chlorine attacks a moist mucous membrane, hydrochloric acid is formed. The effects of chlorine can hardly be differentiated from hydrochloric acid gas, and Lehmann found that 1·5 per thousand of this latter gas affected animals, causing at once uneasiness, evidence of pain with great dyspnœa, and later coma. The eyes and the mucous membrane of the nose were attacked. Anatomical changes took place in the cornea, as evidenced by a white opacity.

In cases that recovered, a purulent discharge came from the nostrils with occasional necrosis of the mucous membrane. The symptoms in man are similar; there is great tightness of the breath, irritation of the nose and eyes, cough and, with small repeated doses, bronchitis with all its attendant evils. Bleaching powder taken by the mouth is not so deadly. Hertwig has given 1000 grms. to horses, 30 grms. to sheep and goats, and 15 grms. to dogs without producing death. The symptoms in these cases were quickening of the pulse and respiration, increased peristaltic action of the bowels and a stimulation of the kidney secretion. The urine smelt of chlorine.

§ 45. Post-mortem Appearances.—Hyperæmia of the lungs, with ecchymoses and pneumonic patches with increased secretion of the bronchial tubes. In the mucous membrane of the stomach, ecchymoses. The alkalescence of the blood is diminished and there may be external signs of bleaching. Only exceptionally has any chlorine smell been perceived in the internal organs.

§ 46. Detection of Free Chlorine.—The usual method of detection is to prepare a solution of iodide of potassium and starch and to soak strips of filter-paper in this solution. Such a strip, when moistened and submitted to a chlorine atmosphere, is at once turned blue, because chlorine displaces iodine from its combination with potassium. Litmus-paper, indigo blue or other vegetable colours are at once bleached.

To estimate the amount of chlorine a known volume of the air is drawn through a solution of potassium iodide, and the amount of iodine set free, determined by titration with sodic hyposulphite, as detailed at p. 74.