"The Lyotrope Series and the Theory of Tanning," Bennett, J.S.L.T.C., 1917, p. 130. "The Swelling of Gelatine," Bennett, J.S.L.T.C, 1918, p. 40. "The Swelling of Gelatine," Procter, _J.C.S. Trans._, 1914, =105=, 313; and _Koll. Chem. Beihefts_, 1911, =2=, 234. "The Swelling of Gelatinous Tissues," Procter, J.S.C.I., April 16, 1916. "Summary of Procter's Views, and Bibliography," Collegium (London), p. 3, 1917. "Lyotrope Influence and Adsorption in the theory of wet work," Bennett, J.S.T.C., 1920, p. 75. For the "finger test," see-- "Glue and Glue Testing," Rideal, 2nd ed., p. 158. "Leather Trades' Chemistry," Trotman, p. 241. SECTION II.--RAW MATERIALS AND PRELIMINARY TREATMENT The raw materials for the manufacture of gelatine and glue may be classified according to their origin. The preliminary treatment, which comprises chiefly purifying and cleansing operations, is varied according to type of manufacturing process for which it is a preparation. In the case of hide or =skin gelatine=, the raw material is a bye-product of the leather industry. After the hides or skins have passed through the preparatory processes which convert them into "pelt" (see Part I., Section II.), they are so trimmed that all that is left will make a useful leather. These "trimmings" or "roundings" include ears and noses, the udders of cows and heifers, and also include parts from the butt, belly and shanks which are collectively termed "pieces." The operation of fleshing (Part I., Section II.), in which fat and flesh are cut from that side of the hides and skins which was next the flesh, also involves cutting into the collagen to some extent, and these "fleshings" comprise another very large class of raw material. The fleshings obtained by hand labour contain distinctly more hide substances than those obtained by machine work, and their commercial value to the gelatine manufacturer is of course proportionate to the collagen content. Some hides and skins are split in the pelt (Part I., Section IX.; Part II., Sections II., III. and IV.), and the "flesh split," though sometimes made into leather, is also used in making gelatine, a high quality being obtained from such material. Minor sources of material are tendons and cartilages, and also hides and skins which have been too much damaged by partial putrefaction or by accidents to make sound leather. Of course the material from the hides for heavy leathers form the greater bulk of raw material for skin gelatine which is thus derived principally from ox hides but sheep and goat skin pieces have also an important place. The skins of other animals, such as dogs, cats, hares and rabbits not usually made into leather can also be depilated and used for making skin gelatine and glue. Horse hide fleshings and pieces are sometimes used, but are notorious for the poor quality of their product. They seem to contain less [alpha] gelatin.