JAPANNING LEATHER.
In November, 1838, William Gates, of Hanover, N. Y., received a patent for preparing and applying elastic japan to leather, to produce the kind now known by the name of “glazed leather.” Two quarts of linseed oil were boiled until the yellow scum disappeared, and two ounces of umber and one of litharge were added and boiled for an hour and a half. The fire was then withdrawn, and all sediment allowed to settle, after which the clear liquor was run off. Eight ounces of India-rubber in shreds were then heated in a close vessel with two quarts of turpentine, and the two quarts of prepared linseed oil described were added, and the whole kept boiling until the India-rubber was dissolved, when eight ounces of asphaltum were added. This constituted the japan for the leather. It was put on the leather with a sponge or brush and allowed to dry, which it did rapidly. It was then rubbed down with pumice stone, then another coat laid on, and so on successively, like varnishing and polishing mahogany or rosewood. This method of japanning leather is now public property.
GUM.
This word stands for a number of substances which, when dissolved in suitable liquids, possess a powerful adhesive property, and the common and well-known gum-arabic may stand as a type of the class. It is the product of an acacia, and was originally imported into Europe from Barbary and Morocco. In its purest condition, it forms white or rather yellowish masses, which are destitute of any crystalline structure, and break with a shell-like fracture. Its solutions are wrongly called mucilage, which is an entirely different substance. Gum-arabic dissolves in cold water, from which the pure gummy soluble principle can be precipitated by alcohol and by basic acetate of lead. Arabin is composed of 42.1 per cent. of carbon, 6.4 per cent. of hydrogen, and 51.5 per cent. of oxygen, which, by a curious chemical coincidence, is exactly the composition of crystallized cane sugar, and it illustrates the fact, that among organic bodies, substances of the same ultimate composition may have very dissimilar properties.
Another gum is mucilage, very abundant in linseed, in the roots of the mallow, in salep, and in the fleshy roots of the orchis and other plants. It is soluble in cold water, but is less transparent than gum-arabic, and it is precipitated by the neutral acetate or sugar of lead.
Gum Tragacanth is chiefly composed of a kind of mucilage to which the name of bassorin has been given, and which does not dissolve in water, but simply assumes a gelatinous aspect. Caustic soda or potash will dissolve it. The principle use to which this gum is put, is in the manufacture of marbled paper, where it forms the bath on which the colors are thrown, and from which they are taken up by the paper.
Cerasin is the insoluble portion of the gum of the cherry tree, and is nearly like bassorin. Mr. Schmidt has determined the composition of these various substances, and has found them all more or less allied to starch, invariably containing hydrogen and oxygen, the proportions in which they form water, and all when treated with acids yield grape sugar.
The jelly of fruits or pectin is closely related to the gums, but as yet chemists have not paid much attention to it, and consequently much that is said of it is merely conjectural.
GUM ARABIC CEMENTS.
Gum arabic, dissolved in as small quantity of water as may be, and diluted to a proper consistence with gin, or any proof spirits, forms a very useful cement for all purposes where gum-water is commonly used, the spirit preserving it from becoming putrescent. As the spirit evaporates, more should be added. It should be stirred and mixed together at the time of using. If plaster of Paris be added to gum-water, it makes a cement useful to ladies in filigree works.