Laboratory manual for the detection of poisons and powerful drugsAuthorized translation of the completely rev4th German ed. . pour the liquidthrough a wetted filter. Ifthe excess of free hydro-chloric acid is not too large,saturate the filtrate directwith hydrogen sulphide asdirected on page 145. Other-wise, evaporate the solutionin a porcelain dish upon thewater-bath nearly to drynessto remove most of the freehydrochloric acid. This stepfrequently gives rise to a darkbrown color which a fewcrystals of potassium chloratewill discharge. In testing forlead, cadmium and copper, itis advisable to
Laboratory manual for the detection of poisons and powerful drugsAuthorized translation of the completely rev4th German ed. . pour the liquidthrough a wetted filter. Ifthe excess of free hydro-chloric acid is not too large,saturate the filtrate directwith hydrogen sulphide asdirected on page 145. Other-wise, evaporate the solutionin a porcelain dish upon thewater-bath nearly to drynessto remove most of the freehydrochloric acid. This stepfrequently gives rise to a darkbrown color which a fewcrystals of potassium chloratewill discharge. In testing forlead, cadmium and copper, itis advisable to evaporate,because hydrogen sulphideprecipitates the first twometals incompletely, or notat all, from solutions contain-ing too much alternative procedure consists in removing part of thefree hydrochloric acid from the filtrate, obtained after treat-ment with hydrochloric acid and potassium chlorate, by firstevaporating to smaller volume and then adding ammoniumhydroxide solution until alkaline. Add dilute nitric acid untilthe solution is faintly acid and saturate with hydrogen sulphide(seepage 145).. Ftg. 12. MKIALLIC POISONS 143 The residue upon the filter may contain silver chloride,barium sulphate and lead sulphate in addition to fat. Examineas directed under Metallic Poisons IV (see page 163). H. Thoms^ destroys organic matter in the apparatus shown in Fig. 12. Oxidation is carried on in an ordinary fractioning flask (A) with the tubulus (B) bent upward. A separating funnel (C), held in the neck of the flask by a stopper, contains an aqueous solution of potassium chlorate (i : 20) saturated at room temperature. The organic matter is in the flask as a thin mixture with per cent, hydrochloric acid. Add about I gram of solid potassium chlorate and warm the flask on a boiling water-bath. When the mass in the flask is warm, let the potassium chlorate solution run in drop by drop and shake constantly. Care must be taken not to add too much of this solutio
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