Provided either starch or flour paste is protected against drying in, it can be kept unchanged for a long time by the addition of a small quantity of carbolic acid.
For hanging wall-paper an addition of alum is, generally speaking, more suitable than carbolic acid.
In hanging wall-paper the wall is generally first sized with glue water. By the alum coming in contact with glue an insoluble leather-like combination is formed, which not only resists decomposition, but by far surpasses ordinary paste as regards adhesive power, so that when the paper is to be removed from the wall it has to be scraped and torn off in small pieces, while that hung without previous sizing of the wall is readily removed in large pieces.
But alum cannot be used for preserving a glue solution, as it would cause it to coagulate to a flaky mass. Carbolic acid is, on the other hand, an excellent means for the purpose, but to prevent its characteristic empyreumatic odor from making itself too sensibly felt, no more than about one two-thousandth of the weight of the glue solution should be added.
Shoemakers’ paste. In addition to being cheap, no other paste adheres as well to leather as the so-called shoemakers’ paste. With it leather can be secured not only to leather, but also to woven materials, paper, etc. Though its preparation is very simple, it is connected with some disagreeable features consisting chiefly in the development of a truly terrible stench.
The paste is prepared by stirring crushed barley with hot water to a thick paste and adding small portions of hot water, so that the temperature of the mass is kept at between 86° to 104° F. In a few days the mass commences to develop gas, which shows at first no odor, but soon the development of gas becomes stronger and an acid odor is perceptible, which in a short time is replaced by a terrific stench which, as before mentioned, affects the olfactory organs in a most unpleasant manner.
In consequence of the acid and putrid fermentation the pasty mass gradually loses its granular condition, and is finally converted into a homogeneous, thickly fluid mass of a brown color, which draws threads between the fingers, and possesses great adhesive power. When this is the case, decomposition, which otherwise would go on until nothing remained but a watery and acid fluid, is interrupted by lowering the temperature of the paste by ladling it from the vat or by adding a small quantity of carbolic acid.
To render the stench developed during the fermentation of the paste innoxious, the vat in which it is prepared should be provided with a well-fitting cover, in which is fitted a stovepipe passing into a chimney connected with a kitchen range or furnace, in which a fire is frequently burnt.
By kneading shoemaker’s paste together with indifferent substances it can be used as a cement for various purposes. The substances best adapted for the purpose are burnt lime slaked to a powder, whiting, zinc white, pipe clay, ochre, etc.
Gum arabic. This gum is an exudation from certain tropical species of acacia, and consists essentially of arabine, which has the composition C12H11O11. The best gum arabic is that in the form of very pale-yellow, brittle pieces; golden-yellow to brownish pieces are not valued as highly, though they give a solution of considerable adhesive power.