The chemical composition of glue is such as to bring to mind that of starch and cellulose derived from the vegetable kingdom. It contains:
Carbon 49.1 per cent.
Hydrogen 6.5 per cent.
Nitrogen 18.3 per cent.
Oxygen and sulphur 26.1 per cent.
which may be represented by the formula: C12H10N2O4.
The composition of glue differs but little from that of the glue-yielding substance. Isinglass is composed of:
Carbon 49.5 per cent.
Hydrogen 6.9 per cent.
Nitrogen 18.8 per cent.
Oxygen 24.8 per cent.
This justifies the assumption that glue in its various transition stages does not represent different chemical combinations, but only modifications of one and the same combination distinguishable from each other by physical characteristics, as is the case with starch, which without suffering an alteration in its composition, appears as dextrine and grape-sugar, or as with cellulose, which, without altering its composition, can be transformed into amyloid and grape-sugar.
[CHAPTER II.]
USES OF GLUE.
An inquiry into the various technical uses of glue must be of interest to the manufacturer so as to enable him, when acting, as is frequently the case, as salesman, to know to whom to offer his product; and also to learn what special demands he has to satisfy, as not every glue is adapted to every purpose, different qualities being required for special uses.
Glue as a joining medium. In Chapter I, treating of the nature of glue, special attention has been drawn to the fact, that the adhesive power of glutin is greater than that of chondrin; and that glutin obtained from skin and tendons possesses still greater adhesive power than the product from bones. This is the reason why good sound glue made from scraps of skin is preferred by those artisans who may be considered the principal consumers, such as cabinet-makers, carpenters, turners, instrument-makers, wood-carvers, carriage-builders, brush-manufacturers, bookbinders, paper-manufacturers, etc., all of them requiring glue of the greatest possible adhesive power. It must, however, by no means be understood that a good quality of bone glue cannot be used for the same purposes; because much bone glue of excellent quality and at a low price is brought into the market by manufacturers of animal charcoal and bone meal, and is used in glueing wood, etc.