[767] “Arsenic in Glycerin,” by Dr. H. B. H. Paul and A. J. Cownley, Pharm. Journ., Feb. 24, 1894.
§ 740. Arsenic in Organic Matters.—Orfila and the older school of chemists took the greatest care, in searching for arsenic, to destroy the last trace of organic matter. Orfila’s practice was to chop up the substance and make it into a paste with 400 to 700 grms. of water; to this ·010 grm. KHO in alcohol was added, and ·020 grm. of potassic nitrate. The substances were heated up to from 80° to 90° for some time, until they were pretty well dissolved; the organic matter was then burnt off in a Hessian crucible heated to redness, on which small quantities of the matters were placed at a time. When the whole had thus been submitted to red heat, the melted mass was run into an almost red-hot porcelain basin, and allowed to cool. Afterwards, it was again heated with concentrated sulphuric acid, until all nitric and nitrous fumes were dissipated; on dissolving and filtering in water, the liquid was introduced into a Marsh’s apparatus. Orfila never seems to have failed in detecting arsenic by this process. For an organ like the liver, he considered that 100 grms. of potash and 86 of strong sulphuric acid were necessary in order to destroy the organic matters.
The liability of the various reagents used to impurity, and the probability of loss in these operations, have tended to discredit destruction of the organic matter by a red heat, and chemists generally have preferred to oxidise animal matters by a moist process. The organic substance is divided finely and digested with dilute hydrochloric acid, and from time to time crystals of potassic chlorate are thrown in until all the fluid is very thin and capable of passing through a filter. The filtrate must now be submitted to the prolonged action of sulphuretted hydrogen,[768] and the sulphide of arsenic separated from free sulphur by dissolving in sodic sulphide. After filtering, the arsenic sulphide may be again thrown down by the addition of hydrochloric acid, collected on a filter, and still further purified by solution in ammonic carbonate; once more precipitated by hydrochloric acid, and lastly identified by conversion into magnesia pyro-arseniate (see [p. 572]). The above process is a general and safe way of detecting arsenic in almost any organic tissue, but the author prefers the distillation process described [p. 575] et seq.
[768] The SH2 should be washed by passing it through two or more washing bottles supplied with warm dilute HCl—a few samples of sulphide of iron give off an arseniferous gas, so that this precaution is necessary.
From ordinary pills, quack extracts, and similar preparations, drying, powdering, and exhaustion with boiling dilute HCl, will remove the whole of the arsenic, if in a soluble state.
Oils and matters consisting almost entirely of fat, suspected of containing arsenic, are gently heated, and allowed to deposit any insoluble matter they may contain; the oil is then decanted, and, if necessary, filtered from any deposit; saponified by alcoholic potash, the soap decomposed by HCl, the fatty acids separated, and the arsenic looked for both in the first deposit and in the solution, now fairly free from fat, and easy to treat.