In wood construction, especially in joinery and cabinet-making, a process is involved known as gluing, whereby glue is employed to hold the different parts together. In the shop the technical processes of gluing must be emphasized, but in order that the pupil master the processes in an intelligent way, he must know what glue is, the different kinds of glue, how and of what made, and the uses of the different kinds. He must understand the nature of the wood to be glued. In short, to master a process, one must look intelligently for information regarding the materials and tools employed, and then by associating this information with the process in actual practice an intelligent understanding of the principles of the process will follow.

Glue is a viscous substance made from the scraps of hides, horns, hoofs, etc., which accumulate at large packing houses. These scraps are washed in limewater, then boiled and skimmed. When the liquid reaches a certain point, it is strained, cooled in moulds, cut into pieces, and dried upon nets. Glue is manufactured largely in the United States and in all countries where cattle are raised. In some countries, like France and Germany, a great quantity of glue is made from bones, but the quality is not as good. It is said that the best glue in the world comes from Scotland.

In the manufacture of certain kinds of glue isinglass is used. Isinglass is a gelatine prepared from the air bladder of such fish as the sturgeon, cod, weakfish, hake, etc. It is also one of the principal ingredients in prepared jellies, confections, and gumdrops. There is also a kind of isinglass known as "Japanese isinglass." This is prepared from a seaweed. Most of the isinglass made for commercial use comes from Russia, Brazil, and the United States.

Isinglass is used in the manufacture of white fish glue, isinglass glue, and waterproof glue.

White fish glue, or diamond cement, as it is sometimes called, is made of isinglass dissolved in alcohol. Isinglass glue is made by soaking isinglass in cold water; when the isinglass is swelled enough, it is put into spirits of wine and heated in a bottle plunged in a bath, with powdered chalk added. Waterproof glue is made by boiling two ounces of isinglass to a pint of skim milk until the requisite consistency is obtained.

Marine glue is made of shellac and caoutchouc, equal parts, dissolved in separate portions of naphtha, and then mixed. Marine glue is insoluble in water and is therefore used largely in shipbuilding.

There is also an albumen glue which is made of partially decomposed gluten obtained from wheat flour in the manufacture of starch.

Caseine glue is manufactured from curds of milk. It is an excellent glue for manual training work. There is another article of a similar nature on the market called dextrineglue; this is manufactured from potatoes and corn.

The uses to which glue is put are many. Among some of the more important might be mentioned, in addition to joinery and cabinet making, paper making, match making, bookbinding, in making sizing for paper hanging, etc. In the manufacture of hats and bonnets it is used for stiffening straw, cotton, etc. It is the glue in the straw that makes one's hat have a sticky feel when wet. Glue comes to us in flakes to be prepared for use, or in liquid form ready for use. For woodwork it is better to buy the ordinary flakes and prepare them as the glue is needed. There are different grades of glue, but it is well to buy the best grade, which costs about twenty cents per pound. A poor quality of glue is worse than no glue at all. It is worthless. Glue is prepared in a glue heater.