Metallic arsenic is not used in medicine. It is steel-coloured, crystalline, and brittle, and when heated gives off garlicky fumes. Very light (sp. gr. 5.8), very volatile. It forms two classes of salts. In one - the arsenious salts - it is tri-, in the other - arsenic salts - pent-atomic. Arsenious oxide, As203, usually called arsenious acid, forms arsenites. Arsenic oxide, As205, or arsenic acid, forms arsenates, or, as they are termed in the B. and U.S.P., arseniates.

General Sources of Arsenic. - It occurs in many ores combined with metals, oxygen, and sulphur. Its presence as a frequent impurity in sulphur has already been mentioned (p. 543). It is chiefly obtained by roasting the arsenides of iron, nickel, and cobalt, and condensing the arsenious oxide in a long, nearly horizontal, chimney.

General Tests for Arsenious Acid. - With hydro sulphuric acid it gives a yellow precipitate, which is brightest in acid solutions. Silver nitrate gives a canary-yellow and copper sulphate a brilliant green precipitate (Scheele's green). These are very soluble in acid, and neither of them is thrown down from simple aqueous solutions of arsenious acid (a little acid being freed in the reaction); a little alkali must be present. Both are very soluble in excess of ammonia, so that to avoid adding excess ammonio-nitrate of silver and ammonio-sulphate of copper are used as reagents, in preference to adding ammonia, along with simple solutions of nitrate of silver or of sulphate of copper. Arseniates throw down a brick-red precipitate with ammonio-nitrate of silver, and are thus distinguished from arsenites.

General Reactions Of Arsenic, Antimony, And Bismuth

Arsenic

Antimony

Bismuth

Hydrosulphuric acid

Yellow precipitate (soluble in ammonium sulphide and re-precipitated by acids).

Orange or brick-red precipitate (soluble in ammonium sulphide, and precipitated by acids).

Black precipitate (insoluble in ammonium sulphide).

Water .......................

...................................

Strong solution thrown into much water gives a white precipitate, which becomes orange on the addition of hydrosulphuric acid.

Strong solution thrown into water gives a white precipitate, which becomes black on the addition of hydrogen sulphide.

General Action of Arsenic. - Although arsenic, like antimony, has no great affinity for albumen, and does not produce with it a coagulum, yet when applied to the skin denuded of its epidermis, it acts as a caustic and produces a slough. If used in a dilute form, and over a large surface, it may be absorbed, and may produce the general effects of the drug upon the system. When applied in a concentrated form it appears to produce a slough more rapidly, and the dead tissue forms a barrier to its further absorption. In the mouth it has a somewhat sweetish taste, and in small doses excites in the stomach a feeling of appetite. In larger doses it produces irritation, colicky pains, diarrhoea, and mucous evacuations, sometimes tinged with blood. In still larger doses it causes symptoms of gastro-enteritis, vomiting, and purging, the stools being finally of a rice-watery appearance, closely resembling those of Asiatic cholera. These are also occasionally accompanied by collapse, with pale, pinched, and somewhat livid surface, and violent cramps of the extremities, so that cases of arsenical poisoning may be readily mistaken for cholera, and vice versa. There is sometimes strangury, priapism, suppression of urine or bloody urine; the consciousness is retained to the last. In some cases there are no symptoms at all of gastro-intestinal irritation, the nervous system being affected, and the patient presents the symptoms of coma, very much resembling those of opium-poisoning.

The treatment in cases of arsenical poisoning is to wash out the stomach freely by means of the stomach-pump, and the copious administration of diluents, taking care to ensure their evacuation by the subsequent speedy administration of such emetics as mustard or sulphate of zinc if they are not at once rejected by the vomiting caused by the arsenic itself. Freshly-prepared peroxide of iron may be administered in doses of a tablespoonful every ten minutes, and alcohol has been given when the moist peroxide could not be obtained. Demulcents should afterwards be given to allay the irritation.

Chronic poisoning by arsenic may occur from the inhalation of arsenical vapour or dust, arising from wall-papers, dresses, or other substances containing arsenic. The proportion of arsenic necessary to produce poisoning when taken into the lungs in this way appears to be very small. The symptoms are at first increased appetite, then colicky pains and mucous or dysenteric stools, with great prostration, irritation of the eyes, running at the nose, a short cough, which is dry or accompanied by slight expectoration, and a white silvery appearance of the tongue. These symptoms may sometimes continue for months, or even years, without the cause being suspected, until the recovery which ensues upon the removal of the offending wall-paper gives the clue to their cause.

When taken internally for a length of time a condition of tolerance may be induced in the case of arsenic, as well as in that of antimony. This is seen in the arsenic-eaters of Styria, who, beginning with small quantities, are gradually capable of taking larger and larger doses, until they can swallow at once, with safety, as much as five grains. In taking such doses as these they are careful not to take water with the arsenic, so that it is probably slowly absorbed from the stomach, and is, very possibly, rapidly evacuated. Dr. Craig Maclagan watched a noted arsenic-eater swallow his dose, and obtained from the urine which he afterwards passed a considerable quantity of the poison. By using the arsenic in this way, these people are said to undergo much greater exertion than usual without exhaustion, and to be able to ascend the steep Styrian hills without being affected with breath-lessness. Some, no doubt, die in the attempt to acquire the habit, but those who have once become accustomed to the drug appear to continue its use without deriving any harm from it, and, moreover, seem sturdy and vigorous, and live to an old age.

After absorption into the blood, arsenic appears to some extent to modify tissue-change. When a solution of arsenious acid is added to blood outside the body, it retards coagulation, prevents putrefaction, and conserves the form of the red blood-corpuscles.