This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is prepared, according to the process of the British Pharmacopoeia, by heating to redness in a crucible a mixture of arsenious acid, nitrate of soda, and carbonate of soda, pouring the melted mass upon a flagstone that it may harden, and then dissolving out the soluble matter by boiling distilled water. The solution having been filtered, is set aside to crystallize. The crystals are then rapidly dried and enclosed in stoppered bottles. In this process, the arsenious acid is converted into arsenic acid by taking oxygen from the nitric acid of the nitrate of soda, and the arsenic acid thus produced combines with the soda of the nitrate and carbonate to form arseniate of soda; carbonic acid and nitrous fumes escaping.
Arseniate of soda is in transparent colourless crystals, of a somewhat saline slightly acrid taste, very soluble in water, and of an alkaline reaction. When heated it melts, and, if the heat be continued, loses its water of crystallization, and 40.38 per cent. of its weight. Its watery vol. ii. - 22 solution gives with chloride of barium, chloride of calcium, and sulphate of zinc, white precipitates consisting of arseniates of baryta, lime, and zinc; and with the nitrate of silver, a brick-red precipitate of arseniate of silver. it consists of two eqs. of soda 62, one of water of combination 9, one of arsenic acid 115, and fourteen of water of crystallization 126; the acid being tribasic.
Arseniate of soda has the same effects on the system as the other preparations of the metal, but is thought to be somewhat milder than arsenious acid and its compounds. it may be employed for the same purposes as the other arsenicals. Dr. Bouchut uses it as a corroborant in the scrofulous diathesis, and asserts that under its use children have their appetites improved, and gain colour and strength. in developed scrofula, it is also often very useful; but in the forms of the disease usually recognized as incurable, such as tubercles in the lungs, bones, etc., it acts solely as a palliative. it is, however, only in very small doses, insufficient to affect the stomach or bowels unpleasantly, that it can be used appropriately in these cases. He begins with about one-fourteenth of a grain, and increases gradually to one fourth of a grain, beyond which it is apt to produce gastralgia, vomiting, or diarrhoea. Being very soluble, it may be given simply with mucilage, or in solution with compatible adjuvants, such as syrup of cinchona, claret wine, etc. (See Am. Journ. of Med. Sci., July, 1861, p. 265.) Though not disposed to doubt the facts stated by M. Bouchut, I should explain the results differently, and ascribe the reconstructive powers which he supposed to be possessed by arsenic to the alterative influence exerted by it on the morbid diathesis, on the removal of which nature exercises her ordinary recuperative powers. Much more accordant with my views of the action of arsenic is the statement made by Dr. Lemare Piquot, physician of the hospital at Honfleur, that, if the blood of a patient who has taken arsenic in the ordinary way for thirty or forty days be compared with its previous condition, it will be found to have suffered a remarkable loss of red corpuscles. On this basis, indeed, Dr. Piquot rests his recommendation of arseniate of soda in cases of apoplectic congestion, attended with an increase of the red corpuscles, or in other words, a plethoric state of the circulation. He has derived advantage from this treatment in upwards of forty cases. His method is to give the arseniate in very minute doses for six weeks or two months. (Ranking's Abstract, No. 31, p. 53; from Gaz. Hebdom. de Med. et Chirurg., Jan. 20, 1860.)
Under the name of Pearson's arsenical solution, made in the proportion of one grain of the salt to a fluidounce of water, arseniate of soda has been long used in Great Britain; but it was first adopted as officinal at the formation of the national Pharmacopoeia. The British officinal solution is much stronger than Pearson's, containing four grains of the anhydrous salt in a fluidounce of distilled water. The dose of the crystallized arseniate of soda is stated at from one-twelfth to one-third of a grain; that of the British officinal solution at from three to five drops or minims, to begin with.
Arseniate of soda has recently been highly recommended by M. Gueneau de Mussy, in the form of bath, in the treatment of that obstinate affection of the joints, now generally recognized by the name of rheumatic gout. Dividing the disease into two forms, one consisting of an indefinite succession of acute attacks, and chronic by its duration, the other truly chronic both in its degree and persistence, he treats the former with arseniate of soda alone in a common or gelatinous bath; in the latter, combines the carbonate of soda with the arseniate. in the simple arsenical bath, he uses from 15 to 45 grains of the arseniate of soda in each bath; in the compound bath, three and a quarter ounces of carbonate of soda, and 15 grains of the arseniate, rapidly increased to 30 grains, which he rarely exceeds. At first he gives a bath every other day, but afterwards daily, with the occasional omission of a day. in some instances, the patient has during the earlier baths complained of pain in the diseased joints; but almost all, on leaving the bath, have experienced an unwonted feeling of relief, and capability of locomotion. With a few, diarrhoea or nausea followed the first baths; in others, a brief excitement, agitation, and inability to sleep; in others, again, an erythematous eruption on the skin. Arsenic was in no instance detected in the urine. The continuance of the treatment depended on the resistance of the disease. in one obstinate case, as many as sixty baths were taken. M. Gueneau de Mussy conjoined with the use of the bath the internal administration of a decoction of guaiacum, with extract of cinchona, and iodide of potassium; but he had never obtained any beneficial effects from this mixture before he began with the baths, though he had used it for fifteen years. The same treatment was found useful in all forms of chronic rheumatism, in certain cases of neuralgia, in one instance of rheumatic paraplegia, and in some chronic cutaneous diseases. (Banking's Abstract, No. 34, p. 39; from the Gaz. des Hopitaux, Aout 10, 1861.)
Other compounds of arsenic acid besides the arseniate of soda above described, have also been used-as the arseniates of potassa, ammonia, and iron; but they have no advantage, as arsenical preparations, over those above treated of; and, in reference to the arseniate of iron, it would be better, in cases in which its two ingredients may be indicated, to employ them separately; as we should thus be guided in the dose of each by the wants of the case, and not by the rigid limits of chemical affinity.