Formula

As2O3.

Arsenic-Arsenicum, the metal from which arsenious acid is obtained, is not employed as a medicine in its native state. It is combined with sulphur and certain metals, and is hard, brittle, crystalline, of a steel-gray color. When heated to a dull redness, it volatilizes in the form of a colorless vapor, with an odor like that of garlic - alliaceous. It is generally found in cobalt ore. It is a powerful poison.

Derivation

Arsenious Acid is obtained by roasting arsenical ores, and purifying by sublimation. It is in the form of a fine white powder, which is often adulterated with chalk, lime, etc.; hence it is better to procure it in the solid form or lump, which is of a milk-white color externally, and often perfectly transparent internally. It has no odor, and is therefore liable to be mistaken for more innocent substances, and scarcely any taste, or merely a faint, sweetish impression.

Medical Properties And Action

Arsenious Acid in large doses is a virulent irritant poison, but in doses of one-sixtieth to one-twelfth of a grain, properly administered, is a tonic increasing the appetite and improving the secretions, both in quality and quantity. In large doses, in the form of Fowler's Solution - Liquor Potassii Arsenitis (prepared by boiling 64 grains of arsenious acid and bicarbonate of potassium, each in half a fluid ounce of distilled water, then adding 12 fluid ounces more of distilled water, half a fluid ounce of compound spirit of lavender, and afterwards water enough to make the solution measure a pint) - it is a powerful antiperiodic. In small doses, administered for a considerable time, it modifies the blood, and through it nutrition, so as to remove various morbid conditions. When continuously used, a sensation of heat in the throat, oesophagus and stomach is sometimes experienced, nausea, pain in the stomach and occasional vomiting ; also, great languor or depression of spirits, with redness of the eyes, swelling of the eyelids and oedema of the face; hence, at the first evidence of such symptoms, the remedy should be discontinued until they have passed away. When continually increasing doses are administered, the arsenic accumulates, and poisonous symptoms quickly appear; hence, it is recommended to begin a course of arsenic with large doses, and the quantity given regularly reduced. When arsenious acid is administered, the bowels should be well evacuated by a purgative, given previously, and the arsenic taken directly after a meal, but never upon an empty stomach, on account of gastric irritation. Its use should be omitted for a day or two every two or three weeks, and a mild aperient employed, in order to prevent the accumulation of the arsenic in the system. A few drops of laudanum added to the arsenical preparation will prevent nausea and vomiting. All arsenical preparations should be administered with the greatest regularity, at stated times.

During the employment of arsenic, the eyes of the patient should be examined daily, and if the eyelids and conjunctiva become inflamed, the remedy should be discontinued; also, when the urine, from being pale and copious, becomes scanty, acid and high-colored, the arsenic should be suspended.

Poisonous symptoms have been caused by half a grain of arsenious acid, and fatal effects have followed the administration of two grains, although much larger quantities have been taken with impunity ; very large quantities often cause emesis, which removes the substance from the stomach, and thus prevents fatal effects. When the idiosyncrasies of the patient are unknown, it is better to use small doses before beginning with large doses. The quantity of arsenic required to produce a fatal effect varies according to the susceptibilities of the patient and the state of the stomach. Much, however, depends on the idiosyncrasies of the individual, which differ greatly in different persons. When large quantities are taken, the effects are sometimes manifested on the cerebro-spinal system, death following, from narcotism, in a short time.

The amount of arsenious acid which may be safely introduced into the stomach should never be equaled in an application to the pulp of a tooth. One-twentieth of a grain may be a safe dose medicinally, but a much less quantity is sufficient for devitalizing the pulps of teeth.

When arsenious acid is swallowed or applied to a denuded surface, it is rapidly absorbed into the system; hence it is a dangerous agent, and in every case it should be carefully used, and its effects closely watched. It possesses a very powerful antiseptic property, arresting the process of putrefaction. The stomach and alimentary canal of persons who have died from its effects have been found in a perfect state of preservation for a long time after interment.

Poisonous doses produce great intestinal inflammation, with ulceration in some cases, and rarely, gangrene. It has also been detected after death, in the blood, in the urine, and also in the liver, spleen, kidneys, muscles and stomach. A certain degree of tolerance in the use of arsenic may be established, when poisonous doses can be taken with impunity. Such a state may be produced by the constant legitimate use of the agent, or in the case of those who begin the habit of arsenic eating at an early age, and who find this practice of service in increased breathing power, strength, and improved bodily condition. As long as such a habit is continued, no ill effects are apparent; but as soon as the arsenic is discontinued, symptoms resembling those of poisonous doses make their appearance.

Arsenious acid acts locally as an escharotic, but while a true escharotic acts chemically, producing decomposition of the part to which it is applied, a state incompatible with life, arsenic destroys the vitality of the organized structure, and its decomposition is the consequence. This distinction should be remembered in the use of arsenious acid in dental practice.