(Also known as Anhydrous Sodium Arsenate.)

Description and Properties. - An amorphous, odorless, white powder, Na2HASO4. Permanent in dry air. Soluble in 3 parts of water; very soluble in boiling water.

This is prepared from sodium arsenate by expelling by heat the seven molecules of water of the latter. The hydrous sodium arsenate (sodii arsenas, U. S. P.) is efflorescent in dry air and somewhat deliquescent in moist air; hence the percentage of arsenic is somewhat uncertain. The new preparation is permanent in dry air. The hydrous sodium arsenate contains 40.4 per cent. of water; hence, a given weight of this substance will contain but little more than half as much arsenic as an equal weight of the exsiccated. The average dose of the latter is accordingly placed at about one-half that of the former.

Dose. - Average dose: 1/20 grain (0.003 Gm. = 3 milligrammes), U. S. P.

Official Preparation

Liquor Sodii Arsenatis - Liquoris Sodii Arsenatis - Solution of Sodium Arsenate (Pearson's Solution). - Strength, 1 per cent. of sodium arsenate. Dose. - 1-10 minims (0.06-0.6 Cc.) [3 minims (0.2 Cc), U. S. P.].

Antagonists and Incompatibles. - Arsenic is incompatible with the salts of iron, silver, magnesia, lime, copper, ammonium, and with vegetable astringents.

Synergists. - Iron and general tonics are synergistic to arsenic.

Physiological Action. - Externally and Locally. - Arsenic itself is largely inert. It is partially oxidized, however, particularly in the intestinal canal, and the arsenous acid ion H3AsO3 and the anhydride, As2O3, are converted into arsenites and are active. Applied to the skin, arsenic acts as a caustic, exciting violent inflammation. Its escharotic influence results in destruction of vitality in the affected parts, accompanied with sloughing. Arsenic may be absorbed from the unbroken skin. Skin eruptions are frequent under arsenical applications.

Internally. - Digestive System. - Except in exceedingly small doses arsenic acts as a gastro-intestinal irritant. Minute and medicinal doses stimulate the flow of gastric and intestinal juices, and augment peristalsis, improving the digestive and nutritive functions. When too long continued, the drug produces nausea, diarrhea, and increased micturition, with a sensation of heat and dryness of the throat and stomach. Toxic doses are followed by violent gastroenteritis. Indeed, in whatever manner introduced into the system, arsenic has a marked action upon the gastro-intestinal tract, causing vascular changes, in the nature of dilatation of the capillaries, which when prolonged bring about destructive lesions. (See Chronic Poisoning.)

Circulatory System. - Cardiac action may be slightly stimulated by small doses, the experience of arsenic eaters proving that the drug, so far from being necessarily deleterious, actually tends to invigorate the heart action for a time at least. Large doses render the heart irritable and feeble.

On the blood-making organs, arsenic has a distinct action, though as yet not definitely understood. New-formed blood-cells have been found, and the spleen and long bones seem to be stimulated to increased blood-making activity. Arsenic in its relations to chronic poisoning shows itself to have a destructive action on the minute blood-vessels. It seems, in common with many other substances, to increase the clotting properties of the blood-serum. Capillary thrombi are constant features of chronic toxemia.

Nervous System. - The general effect of arsenic upon the brain and nervous system is that of a tonic. The cerebral functions are somewhat stimulated.

The grade of stimulation caused by arsenic is difficult to determine, as other factors, notably its action on the skin and blood, should be borne in mind. In chronic poisoning (q. v.), even from very minute doses, the nervous system is markedly affected, particularly the peripheral nerves, both motor and sensory.

Under prolonged use arsenic tends to accumulate to a greater extent in nervous than in other tissues. Thus, according to Scolosuboff, if 1 part is found in fresh muscle, the proportion in the liver is 10.8; in the brain, 36.5; in the spinal cord. 37.3.

Respiratory System. - Ordinary amounts effect no special change in respiration other than increased power and stimulation of the respiratory center. It has been held, with authority, that small doses stimulate the peripheral endings of the pulmonary vagi. In toxic doses arsenic acts as a powerful respiratory depressant.

Absorption and Elimination. - Arsenic is readily absorbed by the blood. Its presence has also been detected in the viscera, bile, urine, sweat, the bronchial and intestinal mucous membranes, and even in the parenchymatous tissues. It is eliminated slowly from the body by the intestines, and rapidly by the urine; possibly, also, by the bile and the skin. The saliva, milk, and even the tears are said to share in the process of elimination.

Medicinal doses prevent tissue-change, while large doses increase nitrogenous metamorphosis. The therapeutic action is certainly to modify and improve nutrition. Binz has suggested the novel idea that the main activity of arsenic is due to its peculiar oxidizing properties by which arsenous acid is oxidized to arsenic acid, which in turn is reduced to arsenous acid, etc. Thus the alternating oxidation and reduction would account for its stimulating general metabolic activity.

Temperature. - The temperature is unaffected by medicinal doses. Chronic intoxication may be accompanied by a rise in temperature.

Eye. - Large doses, or small doses repeated, are followed by injection of the conjunctivae, eczema, inflammation, and edema of the lids. This is a manifestation of the general engorgement of the capillaries of the gastro-intestinal and respiratory tract mucosa.

Untoward Action. - Differing from the characteristic symptoms of poisoning occasionally produced by medicinal doses in very susceptible persons, there are induced, not infrequently, restlessness, headache, alopecia areata, bronchitis, hoarseness, disturbances of digestion, thirst, coryza, and, in rare cases, epistaxis, anaphro-disia, icterus, lacrimation, photophobia, amblyopia, dermatitis, and various cutaneous eruptions, frequently followed by desquamation.