Glue. The hotter the glue, the more force it will exert in keeping the two parts glued together; therefore, in all large and long joints the glue should be applied immediately after boiling. Glue loses much of its strength by frequent re-melting; that glue, therefore, which is newly made, is much preferable to that which has been re-boiled. In melting ordinary glue in the double vessel containing water, it is an excellent method to add salt to the water in the outer vessel. It will not boil then, until heated considerably above the ordinary boiling point; the consequence is, the heat is retained, instead of passing off by evaporation, and when the water boils, the glue will be found to be thor-ougly and evenly melted.

2278. To Prevent Glue from Cracking

2278.    To Prevent Glue from Cracking. Glue is often found to crack in very dry localities, particularly when the objects glued together are not in close contact, but have a thin layer of glue between them; in which case they sometimes fall apart. Very thin layers of glue are not only exceedingly hard, but also more or less brittle when extremely dry; and, therefore, to prevent this dry and consequent brittle condition, the addition of a very small quantity of glycerine will accomplish the desired end. The quantity of glycerine must be modified according to circumstances.

2279. To Make a Very Strong Glue

2279.    To Make a Very Strong Glue. An ounce of the best isinglass may be dissolved, by the application of a moderate heat, in a pint of water. Take this solution and strain it through a piece of cloth, and add to it a proportionate quantity of the best glue, which has been previously soaked in water for about 24 hours, and a gill of vinegar. After the whole of the materials have been brought into a solution, let it once boil up, and strain off the impurities. This glue is well adapted for any work which requires particular strength, and where the joints themselves do not contribute towards the combination of the work; or in small fillets and mouldings, and carved patterns that are to be held on the surface by the glue.

2280. A Strong Glue that will Resist Moisture

2280.    A Strong Glue that will Resist Moisture. Dissolve gum-sandarac and mastich, of. each 1/4 ounce, in 1/4 pint spirits of wine, to which add 1/4 ounce clear turpentine; now take strong glue, or that in which isinglass has been dissolved; then, putting the gums into a double glue-pot, add by degrees the glue, constantly stirring it over the fire till the whole is well incorporated; strain it through a cloth, and it is ready for use. It may now be returned to the glue-pot, and 1/2 ounce very finely-powdered glass added; use it quite hot.

2281. To Make Tungstic Glue

2281.  To Make Tungstic Glue. Tungs-tic glue is prepared by mixing a thick solution of glue with tungstate of soda, and hydrochloric acid, by means of which a compound of tungstic acid and glue is precipitated, which, at a temperature of 86° to 104° Fahr., is sufficiently elastic to admit of being drawn out into very • thin sheets. On cooling, this mass becomes solid and brittle, and on being heated is again soft and plastic. This new compound, it is said, can be used for all the purposes to which hard rubber is adapted.