To ascertain whether antimony was in solution, the liquid contents of the stomach, after dilution with water if necessary, should be allowed to settle, the nearly clear top layer decanted and filtered, and the filtrate examined. The soluble compounds are:—
1. Tartar emetic. Solution slightly acid, taste metallic. On evaporation on a glass slide tetrahedral crystals are obtained. If the solution is moderately strong, it gives a white precipitate with a little hydrochloric acid, soluble in excess: with water it gives no precipitate. Stomach generally inflamed but not corroded.
2. Antimonious chloride, Sb Cl3. Solution strongly acid, effervescing and giving a white precipitate with sodium carbonate. Taste corrosive and powerfully metallic. On evaporation, no tetrahedra. No precipitate with hydrochloric acid: with water a white precipitate, re-dissolved by tartaric acid.[190] By analysis a large quantity of chlorine will be found. The stomach is corroded and often blackened or charred.
3. Antimonates, antimonites, sulphantimonites, and -ates (such as “Schlippe’s salt”), are rare and improbable. Antimonates are alkaline, give a white precipitate with acids, and a white crystalline one with sodium salts. Schlippe’s salt is strongly alkaline, and gives with hydrochloric acid an orange-red precipitate of sulphide.
III. Quantity.
To ascertain the amount of Sb is absolutely necessary. Marsh’s test is not available, since a large part of the antimony is thrown down on the zinc and remains in the generating flask. It has been proposed to wash this off and weigh it, but other metals and impurities are present, so that this is not practicable. Reinsch’s test has been applied quantitatively by weighing the copper before and after the test: the difference of weight was supposed to be the As or Sb. But the copper may dissolve or oxidise, sulphur and other things deposit on it; so that this method is not correct.
If antimony only is present, acidulate with hydrochloric acid, pass sulph. hydrogen in excess, warm, filter, wash the orange hydrated antimonious sulphide into a porcelain capsule, remove most of the water, dry on the water bath, finally at 200°C. and weigh. 100 grains of Sb2 S3 correspond to 85·88 of Sb2 O3, to 196·47 of tartar emetic, to 71·76 of Sb, to 134·41 of Sb Cl3.
But in the stomach any other metal may be present, hence a process of separation must be used. It is not generally necessary to destroy the organic matter: if this be desired, Fresenius and v. Babo’s process, of heating with H Cl and potass. chlorate (previously proved pure) may be used without much danger of loss, as Sb Cl3 is not so volatile as As Cl3. Otherwise the solution made by pure hydrochloric and a little tartaric acids is treated with sulphuretted hydrogen. The precipitated sulphide may be of uncertain, though suspicious colour. After collection on a filter and washing, it should be extracted with dilute ammon. carbonate solution (10 per cent.): arsenic only will dissolve and will be reprecipitated as sulphide on adding an acid. The remainder on the filter must be treated with freshly prepared ammon. sulphide: antimony and tin will dissolve. If any black residue remains on the filter, it will consist of mercury, lead, bismuth, or copper: it should be treated with hot 25 per cent. nitric acid, when all will dissolve except mercuric sulphide. We shall then have three portions:—
1st. The mercuric sulphide. Wash, dry, and weigh. Then heat in a sealed tube with dry sodium carbonate, collect the sublimate of metallic mercury, weigh it, and preserve in a sealed tube.
2nd. The nitric acid solution containing lead, bismuth, and copper. Evaporate nearly to dryness, dilute, add dilute sulphuric acid, and a little alcohol, after standing collect and weigh the precipitated sulphate of lead. Precipitate the bismuth by ammon. carbonate in excess, and the copper from the filtrate by zinc or by sulph. hydrogen. (See Fresenius’ Quant. Anal. p. 411).