Much glue is converted into "size," which is a weak gel used as a filling rather than as an adhesive agent. A low-grade glue is often therefore preferred for such purposes, as having "body" rather than "strength." Size is often sold in cake, but sometimes in the form of the gel itself, in which case it may never have been evaporated. Indeed, size is often overboiled glue, made by crude and out-of-date methods. It is largely used in the paper trade, and for wallpapers, millboards, papier-mache, paper and cardboard boxes, etc. Mixed with logwood and iron, and possibly alum, it formed the "blue size" once largely used by bootmakers as a foundation for blacking, and is similarly used in currying. Size is also used in making oil paints and varnishes. Distemper is a size with which is incorporated whiting or gypsum and coloured pigments. In all applications of size, it is common to use antiseptics. Salicylic acid has been widely used in this sense. Low-grade glue is used for the manufacture of cheap brushes and for fly-papers. Innumerable patents have been taken out and mixtures invented for the production of plastic materials, which frequently involve gelatine or glue. Thus, gelatine and glue are used in making plaster casts, and for imitation ivory, wood, stone, and rubber. Many of these inventions have been investigated by Rideal, who points out the features common to most of them. Usually a viscous sol is thickened by the addition of inert fibres and powders, and with the object of making the preparation more waterproof it is customary to incorporate oils, fats, waxes, tars, and resins before the gel is set. The surface is hardened by "tanning" with formalin or tannin solution, finally painted or varnished. Equally innumerable are the inventions, recipes, and patents for making glues that shall remain liquid. The convenience of this ideal is obvious, but many of the suggestions are useless. It is quite easy to incorporate into a gel substances which keep it liquid--any soluble substances with a lyotrope influence of the iodide type will do this--but these also prevent the glue setting when used. Even in small quantity they will influence the tenacity of the joint. Other methods depend upon a partial hydrolysis of the protein. Amongst the most successful of these attempts are to dissolve 3 parts of glue either in 12-15 parts saccharate of lime, or in 9 parts of 33 per cent. acetic acid. Many special glues and cements are made from commercial glue, according to the purpose required. "Marine glue" contains no glue; it is made from shellac and rubber mixed with benzene or naphtha. Its advantage is waterproofness. REFERENCES. "Glue and Glue Testing," S. Rideal, D.Sc., 2nd ed. "Uses of Glue," chap. iii. p. 83. "Uses of Gelatine," chap. iv. p. 100. "Special Glues," p. 108. "Liquid Glues," p. 119. "Gelatine, Glue, and their Allied Products," T. Lambert. "Uses of Glue and Gelatine," chap. ix. p. 80.