1. Sulphuretted hydrogen gives a bright yellow precipitate of arsenious sulphide (As2S3) in acid solutions of arsenious acid or the arsenites.

2. Hume's Test. - Ammonio-nitrate of silver gives a lemon-yellow precipitate of arsenite of silver (Ag3AsO3) in solution of arsenious acid, or the arsenites. The same silver-salt gives a similar reaction with phosphoric acid, but with arsenic acid and the arseniates, a chocolate-colored precipitate of arseniate of silver (Ag3AsO4).

3. Ammonio-sulphate of copper gives with compounds either of arsenious or arsenic acid a light-green precipitate of arsenite of copper (Cu HAsO3, Scheele's green.

4. Marsh's Test. - Generate hydrogen by the action of a hot solution of caustic potash or soda on zinc (Zn + 2KHO = K2ZnO2 + H1). Fleit-mann has shown that antimony will not combine with this form of hydrogen, but that arsenic will. Place the solution to be tested in a "Marsh's apparatus," and if arsenic be present it will combine with the nascent hydrogen to form arseniuretted hydrogen (As2O3 + 6H1 = 3H1O + 2AsH3). On igniting the jet of gas (which burns with a bluish flame), and depressing upon it a cold porcelain plate, an arsenical stain will be deposited, while the hydrogen is burned off into water. The stain has the following characters: - (a) metallic brilliancy; (b) hair-brown color; (c) volatility; (d) solubility in chloride of lime; (e) non-solubility in cold disulphide of ammonium; (f) when evaporated with a drop of nitro-hydrochloric acid it yields a residue of arsenic acid, which gives a brickdust-red turbidity on the addition of nitrate of silver.

5. Reinsch's Test. - A piece of copper foil, when boiled in an acid solution of an arsenical compound, will become slate-gray from the deposition of a fine film of metallic arsenic. This test, to be complete, must be verified by heating the coated copper in a narrow glass tube, when metallic arsenic will sublime, and be deposited in a ring on the cooler part.

For the "reduction test" of white arsenic, it should be placed with "black flux" in a similar tube perfectly dry, and, on heating first the charcoal and then the arsenic, the latter sublimes and is deposited in a metallic ring as above mentioned.

Absorption And Elimination

Since the observations of Schmidt, Mialhe, and others, metallic arsenic has been considered inert. Recently, however, Schroff has shown that it may exert a strongly poisonous action, and that doses of 8 to 15 gr. have caused gangrene of the stomach and death in thirty to forty hours (Zeitschrift der Arzte, i., 1858). It is probably oxidized before absorption.

Arsenious acid in all its combinations, and by whatever channel introduced - by mouth or by rectum, by the lungs or by the skin - is readily absorbed, and has been detected in the blood a few minutes after its administration. It passes out by the skin and mucous membranes, by the various glands, as the salivary and even the lachrymal, but mainly by the kidneys.

The rapidity of elimination varies; in some cases, none of the substance could be detected in the secretions three days after the last dose, but in Ludwig's observations on animals, if small quantities were given for a fortnight and then omitted, the urine was not quite free till three weeks afterward (Medical Record, 1877). Gubler gives six weeks as the time during which it may continue to pass out, and when it has ceased to do so it may reappear after administration of iodide of potassium; hence it seems probable that elimination is not always complete, and that of what is taken, a part may be deposited in the tissues and occasion so-called "cumulative" effects. Recently, arsenic has been found to be specially deposited in the nervous system; thus, if in fresh muscle 1 part is found, the proportion in liver is 10.8, in brain 36.5, and in spinal cord 37.3 (Scolosuboff: Annales d'Hygiene, January, 1876). This became a matter of great importance in a recent French trial (Danval), when the experts were blamed for not examining the brain and cord (British Medical Journal, ii., 1878, p. 73); these parts should henceforth be analyzed as carefully as the abdominal viscera. Caillol (de Poncy) offers some analyses to show that arsenic partly displaces phosphorus in nerve-compounds (Medical Record, 1878). If any be contained in the body at death, it may be detected after an almost indefinite period.

Physiological Action (External)

Preparations containing arsenic produce local irritation, inflammation, or destruction of tissue, in varying degree, according to the strength and character of the application. Dry white arsenic in mass may not injure the unbroken skin, but arsenical powders are apt to produce eruptions of various kinds on exposed surfaces, and especially irritative effects on the pudenda, in those who are employed in the manufacture of green dresses, wall papers, artificial flowers, etc. (Annales d' Hyginie; Dr. Guy: British Medical Journal, ii., 1863, etc.). Perforation of the septum nasi has been noted, and anal ulceration has followed the local use of a green paper colored with arse-nite of copper. Arsenic dissolved or moistened is still more irritating, and those who use it, for instance, in sheep-washing, generally suffer from eczema of the scrotum, etc. (Lancet, 1857). Those who work with arsenical powders are liable also to various degrees of acute and chronic arsenical poisoning; and green colors are not the only dangerous ones: fuchsine, a red dye, contains much arsenic (Ludwig: Medical Record, 1877), and blue gloves have shown arsenic on analysis (British Medical Journal, ii., 1878). The use of green-colored cards has caused a disease of the nails resembling psoriasis, and green hat-lining has caused eczema (Farquharson: British Medical Journal, ii., 1879). The external use of a violet powder adulterated with arsenic proved fatal to thirteen children out of twenty-nine subjected to it (British Medical Journal, ii., 1878).

The continued application of a strong arsenical compound has a caustic, destructive effect, which is not simply a chemical one, like that of caustic acids or alkalies, and is not exerted on the dead subject (Hirtz), but is produced by interference with nutritive processes in the part, causing rather a condensation and "mummifying" of tissue than an actual destruction (Gubler). It is much more active in unhealthy, ill-nourished tissue (e.g., that of lupus), than it is in normal tissues. Very strong arsenical applications produce much local inflammation, and so far interfere with the action of absorbents that the effect remains local only; but un-less in such strong concentrated form, arsenic is readily absorbed, especially from wounds and mucous surfaces; hence its surgical use has led to serious constitutional symptoms, and even to death. Roux describes the application of an arsenical ointment - 1 part in 32 - over a space of 1 1/2 square inches of a cancerous breast for one night only, and death from poisoning on the second day. Sir Astley Cooper relates a fatal case from the use of an arsenical solution to a "fungus of the eye" (Lancet, i., 1837).

Arsenical paste applied to an inflamed tooth-pulp has also proved fatal, and Graham has recorded vomiting, severe pain, convulsion, and death from the use of a plaster containing half its weight of arsenic to a cancerous breast (Glasgow Medical Journal, 18G9); the prescriber of the plaster was tried for homicide, and many similar cases have been before the law courts.

The antiseptic power of arsenic deserves mention: it is largely utilized in the dissecting room, and seems to have retarded the process of postmortem decay in some cases of poisoning when large amounts have been used. The recent researches of Johannsohn assign it, however, but a limited power: he found that small quantities checked fermentation in yeast and syrup, but only for a time: in lactic fermentation it diminished the growth of one fungus, but favored another. The same thing occurred in urine: it exerted no influence on non-organized ferments, such as pepsin, amygdalin, etc. (Archiv fur Exper. Path., Bd. ii., p. 106).

Physiological Action (Internal)

The blood and the nutrition-processes are altered by arsenious acid and its compounds, but the symptoms of its physiological action are mainly evidenced in the alimentary canal, the mucous membranes, and the nervous system, and in different cases these parts are affected in different degree, according to the dose, the time and mode of its administration, and the constitution of the individual.