264 ANIMAL PROTEINS 



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 sug- 

 gestions 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 com- 

 mercial 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 water- 

 proofness. 



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. 



' Liquid Glues and Cements," chap. viii. p. 69. 



