The pharmacopoeia of the United States of America, 1850.

  • General Medical Convention.
Date:
1851
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Licence: Public Domain Mark

Credit: The pharmacopoeia of the United States of America, 1850. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    29/1902
    Gum arabic undergoes no change by time, when kept in a dry place. Its aque- ous solution, if strong, remains for a considerable time unaltered, but ultimately becomes sour, from the production of acetic acid. The disposition to become sour is increased by employing hot water to dissolve it. The tendency of a weak solu- tion to become mouldy is said to be obviated by adding a few drops of sulphuric acid, and decanting from the sulphate of calcium deposited. (Am. Journ. of Pharm., Aug. 1872, p. 353.) Mixed with chalk and cheese, at ordinary temperatures, the solution undergoes a fermentation, resulting in the production of alcohol, without an antecedent formation of sugar. (Journ. de Pharm. et de Ghim., 3e ser., xxxii. 261.) Between 300° and 400°, the gum softens, and may be drawn into threads. At a red heat it is decomposed, yielding, among other substances, a minute propor- tion of ammonia. When burnt, it leaves about 3 per cent, of ashes, consisting, according to Guerin, of carbonates of potassium and calcium, a little phosphate of calcium, chloride of potassium, oxide of iron, alumina, magnesia, and silica. The lime is now supposed to exist in the gum combined with gummic or arabic acid, and this compound constitutes pure gum or arabin. In consequence of the presence of lime, oxalate of ammonium occasions a precipitate with the solution. Besides pure gum, gum arabic contains a very small proportion of an azotized body, which is thought to occasion a slight opalescence in its solution, several saline substances, and 16 to 17 per cent, of uncombined water. (Guerin.') Pure gum (or more properly gummic acid) may be obtained by treating the compounjd of gum and protoxide of lead with sulphuretted hydrogen. Its ultimate constituents are carbon, hydrogen, and oxygen ; its generally admitted formula being The properties above enumerated belong to gum arabic generally. There are, however, pharmaceutic varieties with differences which deserve notice. 1. Gum that is transparent and readily soluble. This constitutes by far the greater portion of the commercial varieties distinguished by the names of Turkey and Senegal gum. It is characterized by its transparency, ready solubility, and the comparatively slight degree of thickness and viscidity of its solution. Under this head may be included the gomme blanche fendillee of Guibourt. It is distinguished by the whiteness and deficient transparency of the pieces, attributable to the minute cracks or fissures with which they abound, and which render them very brittle and easily pulverizable. This peculiar structure is generally ascribed to the influence of solar heat and light; but is conjectured by Hayne to arise from the exudation of the juice in the frothy state noticed by Ehrenberg. Though the unbroken pieces are somewhat opaque, each minute fragment is perfectly transparent and homogeneous. This variety, in consequence of its prompt and entire solubility, is usually preferred for medical use, and for most purposes in pharmacy. 2. Gum less transparent and less soluble. Guibourt has proposed for portions of this gum the name of gomme pelliculee, from the circumstance that the masses are always apparently covered, on some part of their surface, by a yellowish opaque pellicle. Other portions of it have a mammil- lary appearance on the surface. It is less transparent than the former variety, is less freely and completely dissolved by water, and forms a more viscid solution. It melts with difficulty in the mouth, and adheres tenaciously to the teeth. It is found in all the commercial varieties of gum, but least in that from Egypt. Its pcculiari- 5. According to M. Fr6my, cerasin is nothing more than metagummate of calcium, being, as is well known, changed by boiling with water into arabin, in other words, gummate of calcium, or gum arabic. 6. Hence, M. Fr6my supposes that, in plants, metagummic acid is first formed, which in the progress of vegetation is more or less completely changed into gummic acid, thus giving rise to different varieties of gum, distinguished by the greater or less proportion of the soluble to (he insoluble ingredients. 7. Bassorin, however, when boiled with water and an alkali, though rendered soluble, is not, like cerasin, converted into gum arabic or arabin; the soluble gum which results being precipitated from its aqueous solution by neutral acetate of lead, which is not the case with gum ai’abic. (Journ. de Pharm. et de Ghim., Fev. 1860, p. 81.)—Note to the twelfth edition. Dr. Grraager has recently, in the Net ten Jahrhuch fur Pharmacie (xxxviii. p. 129), published inves- tigations into the chemistry of gum arabic, which confirm while they modify the results of Fremy. He treats especially of the nature and mode of production of metagummic acid: and, according to the author cited, it is this acid and not the gummic which unites with lime, potassa, and magnesia to form gum arabic. The character of this work does not admit of extended statements of matters purely chemical, and we must content ourselves with referring to a translation of Dr. Gricgcr's paper in the Pharm. Journ. and Trans., Jan. 1873, p. 973. (Note to the fourteenth edition.)