The dispensatory of the United States of America / by George B. Wood and Franklin Bache.

Date:
1845
Catalogue details

Licence: Public Domain Mark

Credit: The dispensatory of the United States of America / by George B. Wood and Franklin Bache. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    easily escape detection. Their want of solubility, however, is a ready test. More or less of a similar substance is found in the parcels of gum Arabic from other sources; and we have seen one parcel, said to have come from Barbary, chiefly composed of it. Besides this impurity in the India gum, there are often others more readily detected. Among these, we have ob- served a yellowish-white resinous substance, which has the sensible pro- perties of the turpentines. If proper care be used in assorting this com- mercial variety, it may be employed for all the purposes of good gum Arabic. The India gum is brought into this country partly from Calcutta, partly by way of England. It usually comes in large cases. We have seen a parcel of gum said to have come directly from the Red Sea, enclosed in large sacs made of a kind of matting, and bearing a close resemblance to the gum from Calcutta, except that it was more impure, and contained numerous large, irregular, very brittle masses, not much less than the fist in size. 5. Cape Gum. Pereira mentions that gum has recently been imported into Great Britain from the Cape of Good Hope, where it is collected pro- bably from the Acacia Karroo, which grows abundantly on the banks of the Gariep and in other parts. It is of a pale yellow colour, in tears or frag- ments, and is considered an inferior variety. None of it probably reaches this country. General Properties. Gum Arabic is in roundish or amorphous pieces, or irregular fragments of various sizes, more or less transparent, hard, brittle, pulverizable, and breaking with a shining fracture. It is usually white, or yellowish-white; but frequently presents various shades of red, and is some- times of a deep orange or brownish colour. It is bleached by exposure to the light of the sun. In powder it is always more or less purely white. It is inodorous, has a very feeble, slightly sweetish taste, and when pure dis- solves wholly away in the mouth. The specific gravity varies from 1-31 to 1-48. (Bcrzelius). Gum Arabic consists essentially of a peculiar proximate principle of plants usually called gum, but for which the name of arabin,* * Much confusion has existed in the use of the word gum, which has been employed to express various concrete vegetable juices, and, at the same time, a peculiar proximate principle of plants. It is now proposed to restrict the term to the former of these appli- cations, and to designate the principle alluded to by a distinct name. Within a few years the subject of the gums has been investigated by M. Guerin, who has repealed and cor- rected the experiments of former chemists, and thrown new light upon the nature nf these substances. Several of the facts mentioned in the text have been derived from his me- moir, published in the Ann. de Chim. et de Phys., t. xux, p. 248. M. Guerin considers as characteristic of gums, the property of affording mucic acid, when acted on by nitric acid. He recognises in the different gums three distinct proximate principles; namely, ]. arabin, or the pure gum of chemical writers, which is the essential constituent of gum Arabic in all its varieties; 2. bassorin, which enters largely into the composition of Bas- sora gum and tragacanth; and 3. cerasin, which constitutes the portion of cherry gum insoluble in cold water. Of arabin sufficient is said in the text. Bassorin will be treated of under the head of Bassora gum. (See Appendix.) Of cerasin it may be proper to say a few words in this place. The gums which exude from the cherry, apricot, peach, and plum trees, and which the French call gomme dii pays, appear to be identical in compo- sition, consisting of a portion soluble in cold water, which is arabin, and a portion inso- luble, which was formerly thought to be the same with bassorin, but has been proved by M. Guerin to be different, and is appropriately denominated cerasin. This principle is colourless, semitransparent, tasteless, inodorous, uncrystallizable, insoluble in alcohol, in- soluble in cold water, in which it softens and swells a little, and convertible by the action of boiling water into arabin, with which it appears to be isomeric. In this last property it differs materially from bassorin, which is not changed by boiling water. M. Guerin suggests that the natural heat of the climate, in tropical countries, produces the same effect upon the exuded gums as artificial heat in colder regions, and that consequently the acacia gum consists chiefly of arabin.—Note to third edition.