Arsenic is not naturally present in the body (Sonnenschein, Gerichtlich. Chemie, p. 122; and others). As it occurs in soils, in cases of disinterment a portion of the earth surrounding the coffin should be tested.[138]
When absorbed, it may pass into every part of the body, but more especially into the liver and spleen. De Poncy and Livon have supposed that it was capable of replacing phosphorus in the actual brain substance (Comptes Rendus, 23, June 9th, 1879), and that it is mainly localized in the brain. Another author finds it concentrated in the bones. Prof. E. Ludwig of Vienna, in the case of a woman who suffered from making artificial flowers coloured with magenta containing arsenic, found arsenic in the liver, spleen, kidneys, and stomach, but not in the bones or urine (Lond. Med. Record, Dec. 15th, 1877, p. 509). He found also that in human beings as well as dogs poisoned with arsenic, in both acute and chronic cases, the liver contained the largest amount, the kidneys sometimes a considerable quantity, and the bones, brain and urine, only small traces (Jahresb. für Thierchemie, 1879, 85). These results have been discussed by Johnson and Chittenden (American Chem. Journal, 2, 332), who, in a woman poisoned by arsenic, found, a year and a half after burial, over 5 grains of As2 O3, almost evenly distributed. The conclusion to be drawn is, that, of the absorbed arsenic, the main part will be in the liver, and the rest in varying proportions in other tissues, so that as much as possible of the whole body should be examined.
As the large quantity of organic matter is in the way of the tests, it has been proposed to get rid of this by different processes. That of Fresenius and V. Babo consists in oxidizing the substances by strong hydrochloric acid and chlorate of potash. There is a great objection to this, as loss is liable to occur from volatilization of arsenic trichloride, unless it is done in a retort, which is practically impossible on account of the bulk and frothing, and the danger of explosion from the oxides of chlorine formed.
The following modification of an old process has been found by the author to be satisfactory. It may be used also for antimony and mercury. Weigh the whole, cut up finely, and grind the matters to a pulp with water, reserving a weighed portion of about one third; render strongly alkaline with potash or soda previously tested for arsenic. Pass in a current of chlorine, stopping before the alkalinity is destroyed. Boil the solution down to a low bulk, not to dryness, till a portion taken out and treated with acetic acid gives no chlorinous odour, showing that the hypochlorite has been completely decomposed. Arsenic trichloride does not escape from alkaline solutions, so there is no loss. Add sufficient pure aqueous sulphurous acid, to reduce the arsenic acid to arsenious. Now transfer to a large retort provided with a tube-funnel and condenser, the end dipping into water in a well-cooled tubulated receiver, itself connected by a tube with a flask containing dilute potash solution. Through the tube-funnel pour in pure concent. sulphuric acid in volume about equal to the liquid, adding it gradually, as there is much heat and effervescence. Mix well by shaking, and distil slowly from a sand bath. In distilling a moderately strong solution of mixed arsenious and antimonious chlorides in concent. hydrochloric acid, I have found that the arsenic all comes over in the first third of the distillate, and that after two-thirds have passed over, the antimony also begins to distil. Hence, in the above process the distillation should not be carried beyond half the volume of the liquid in the retort, when all the arsenic, in whatever form it originally existed, will be found as chloride in the receiver, except a little which may have escaped into the potash. Test a portion of the potash solution by Marsh’s or Reinsch’s process as hereafter described: if any arsenic be present, add the remainder to the liquid in the receiver, taking care that excess of free acid is left. Pass into the distillate washed sulphuretted hydrogen in excess (or add a solution of the gas in water), warm, cover, and allow to stand. (The excess of sulphuretted hydrogen may afterwards be removed by warming and passing in carbonic acid gas.) If any arsenic be present, a yellow precipitate of arsenious sulphide, As2S3, will appear; if the precipitate be pale, it will consist mainly of sulphur, formed by the action of the sulphuretted hydrogen on the sulphurous acid which is present. Some organic matters are also generally present. Collect the precipitate on a filter, wash with sulphuretted hydrogen water, dissolve in a dilute solution of ammonium carbonate, and again precipitate with hydrochloric acid. The precipitated arsenious sulphide is now nearly pure: it may be collected on a small filter, washed rapidly, again dissolved in ammonia, the solution received in a porcelain dish, evaporated to a low bulk, transferred to a weighed porcelain boat, and heated cautiously in a current of carbon dioxide to a temperature not above 400° C., sufficient, in fact, just to melt the arsenious sulphide. [Sulphur boils at 446° C., As2S3 at 700° C.] Any remaining sulphur is thus removed, and the arsenious sulphide may then be weighed. The weight multiplied by 0·805 gives the amount of arsenic trioxide.
A less preferable way is to collect the arsenious sulphide on a weighed filter, to dry, and dissolve out any sulphur by carbon disulphide. Yet another method is to oxidize by nitric acid, evaporate, precipitate the arsenic acid by a mixture of ammonic chloride, magnesic sulphate, and strong ammonia —“magnesia mixture”) as ammonio-magnesic arsenate, and weigh, either as that salt, or, after ignition, as pyroarsenate of magnesia. The former, dried at 100° C., contains 39·57, the latter 48·29 per cent. of As. Lastly, if the sulphide, oxidized by nitric acid, be alkalized with ammonia, and warmed to 70° or 80° C. with a solution of ammonium molybdate in nitric acid, as used for the ordinary determination of phosphates (see Fresenius, Qual. Anal., p. 54), a yellow precipitate of arsenomolybdate of ammonia appears, which can be weighed: it contains 3·3 per cent. of As (Bull. Soc. Chem., Jan. 7th, 1877).
But where such importance may hang on quantities, the use of weighed filters for such small amounts is simply courting error. When the As2S3 has been weighed in the porcelain boat, calculate it into As2O3, or into As (it contains 61 per per cent. of As), then cover it with a mixture of pure potassic cyanide and sodium carbonate, place it in a piece of combustion tubing drawn out at the end into a long thin point, pass washed dry carbon dioxide over it, and heat cautiously till all the water is expelled. Finally raise the temperature to full redness, and pass a slow continuous current of the gas, keeping the narrow part of the tube cool with moistened blotting paper. The sulphide will be reduced to As, which will deposit in a metallic coating on the narrow portion. Seal this part, and preserve it as evidence.
It is obvious that the residue in the retort may be tested for other metals.
The presence of arsenic ascertained, and the quantity known, it would seem as if nothing more was necessary. Still, it is useful to confirm results by the other tests. The reserved portion may now be divided and used as follows:—
MARSH’S TEST.