remarks on some other methods of detecting arsenic in medico-legal cases, including some of the older processes, may here find their place. Instead of treating, as in the second case, and as described 9, the food, the contents, etc., with hydrochloric acid and chlorate of potassa, I have formerly recommended to digest the substances in a porcelain dish with water, strongly acidulated with hydrochloric acid; the temperature, which, at first, must be very gentle, is gradually increased till near the boiling point, and even raised to boiling if the liquid should not have become sufficiently clear and limpid to admit of a rapid filtration. Arsenious acid, if present, dissolves readily in the acidulated water; starch, if present, is converted into dextrine and sugar; albumen and albuminous substances are coagulated or dissolved; in short, the whole is liquefied. The residue, after having been separated from the liquid by filtration, is treated in the same manner with acidulated water; the liquid portion is again filtered off, and both filtrates are mixed together. Through this solution a current of sulphureted hydrogen is passed (§ 10), and the arsenic, if present, precipitated as sulphide. If, from the liquid, thus treated, no precipitate is deposited, even after twenty-four hours' resting, it is sure to form on evaporation; evaporation, therefore, ought never to be omitted. The liquid, having arrived at that point where the precipitate begins to appear, is again treated, after cooling, with sulphureted hydrogen, to effect a complete separation of the arsenic. The precipitate is collected on a small filter, dissolved in ammonia, and subjected to the treatment described § 11. If the treatment with hydrochloric acid should not happen to afford a liquid fit for filtration, I recommend to strain the liquid through cloth, and to pass through the filtrate a continued current of washed chlorine-gas, until it has become clear, and of wine-yellow color. The chlorine is then expelled by heat, and the liquid treated, after cooling, with sulphureted hydrogen. Fresenius and Babo have raised against this method (the treatment with hydrochloric acid), the well-founded objection, that a perceptible quantity of terchloride of arsenic is volatilized on boiling a solution of arsenious acid in water, containing hydrochloric acid, and that, if the arsenic is present as sulphide, it does not enter, or only partially enters, into solution: § 40. Drunty proposed to remove the organic matter from the extract, óbtained by treating the substances under examination with acidulated water, by means of alcohol, and Brandes corroborated its usefulness for this purpose. On this, Duflos and Hirsch founded their method, described in the above cited work (§ 3, note), which consists in introducing the organic substances, previously cut into shreds, into a tubulated retort, and adding pure hydrochloric acid of 1.08 spec. gr., about equal in weight to the solid. portion of the masses. A receiver, containing about an ounce of water, is attached to the retort, and the latter heated in a chloride of calcium bath. Ebullition is kept up until the greater portion of the liquid part of the contents of the retort have passed over; in other words, until the residue becomes thick and pasty. The retort is allowed to cool, the receiver removed, and the residue mixed with twice its own weight of alcohol. After a while, the mass is thrown on a cloth, and the residue repeatedly washed with alcohol; the liquid is then filtered, the filtrate introduced into a retort, and the alcohol distilled off. What now remains in the retort is mixed with the first acid distillate, which may contain traces of chloride of arsenic, and the whole, after cooling, treated with sulphureted hydrogen. The objections to this method are, that it does not effect solution of the sulphide of arsenic, and that it does not possess any particular advantage. § 41. Graham effects the removal of the organic substances, held in solution, by means of nitrate of silver. The masses under examination are boiled with water, acidulated with a few drops of nitric acid, then strained through a cotton or woollen cloth, and the filtrate mixed with nitrate of silver, until all organic matters are precipitated. The excess of the silver is removed by chloride of sodium, and the filtrate treated with sulphureted hydrogen. This process has the same disadvantage as the preceding; besides, to effect the separation of a liquid containing chloride of sodium from chloride of silver by filtration, is rather precarious. 42. Danger and Flandin destroy the organic matter by concentrated sulphuric acid. The substances are mixed in a porcelain dish with from onesixth to one-fourth of their own weight of concentrated sulphuric acid, and heat applied. The action of the acid on the organic substances consists in converting them into a black, pasty mass, which, with continued heating, assumes the appearance of a dry charcoal. On reaching this point, the dish is allowed to cool; to the cold mass a little concentrated nitric acid, or aqua regia, is added, and the whole again evaporated to dryness. The residue, on being treated with boiling water, affords a limpid liquid, in which the arsenic, if present in the original substances, occurs as arsenic acid; the liquid may be poured into Marsh's apparatus, or may be treated with sulphureted hydrogen, in order to obtain sulphide of arsenic. The sulphuric acid ought to be pure, and, if the liquid is to be tested in Marsh's apparatus, particular care ought to be taken to completely remove the nitric acid by evaporation. The method of Danger and Flandin has more especially been recommended for the examination of the solid organs, as the liver, kidneys, etc., but can, of course, also be employed for the analysis of the contents, food, etc., and blood, bile, etc., after previous evaporation. Owing to the treatment of the dry mass with nitric acid, the arsenic, in this process, is carried into solution, even if it was present as sulphide; but experiments have shown, what might have been à priori expected, that, under the treatment with sulphuric acid, a loss of arsenic, in the shape of terchloride, is experienced, if chloride of sodium, or other chlorides, are present; and the perfect absence of these is perhaps never to be expected. Orfila and Jacquelin obtained, for this reason, always less arsenic in operating after this method, than after effecting the destruction of the organic matters by means of chlorine gas. The process, it is true, is very simple and very convenient. I have obtained myself, in following it, very pure solutions from organs, food, etc., but the defect above stated, makes it much inferior to the process recommended by us. $43. Founded on the observation that arsenic is volatilized as terchloride, when substances containing arsenious acid are heated with hydrochloric acid, or, what amounts to the same, with chloride of sodium and sulphuric acid, a new method for the detection and separation of arsenic, in chemico-legal cases, has been proposed. The substances under examination (food, contents, vomited matters) are placed in a tubulated retort, and a large quantity of chloride of sodium and sulphuric acid added, of the latter not quite sufficient to effect complete decomposition of the salt; the receiver must be well cooled. The distillate contains terchloride of arsenic, if arsenious acid was present. It is essential that the distillation should be carried on for a considerable time, because the greater portion of the chloride of arsenic passes over towards the end of the operation, when the temperature is higher than at the beginning, owing to the more concentrated state of the liquid. An excess of sulphuric acid has to be avoided, because it gives rise to the formation of sulphurous acid, which makes the distillate impure, and unfit to be tested after Marsh's method. Schneider recommends the use of pieces of fused chloride of sodium, or rock-salt, and a gradual addition of the sulphuric acid during the process of distillation, to be poured through a tube with an shaped bend in the middle. This arrangement permits a concentration of the contents of the retort by distillation, previous to the addition of the acid, if too much water should happen to be present.--(Schneider, Lie |