"Liquid Glues and Cements," chap. viii. p. 69. SECTION IX.--THE EVOLUTION OF THE GELATINE AND GLUE INDUSTRY The manufacture of gelatine and allied products has received a great stimulus in this country from the circumstances arising from the European War. The large restriction of continental--especially French and Belgian--supplies of gelatine, led to greater demands for the British-made product, and resulted not merely in a period of greater prosperity, but in a period in which much greater efforts were made to supply a high-grade article in larger quantities. Most manufacturers strove to make high-class gelatine rather than low-grade glue, great extensions were made, and many new businesses were established. The development of the leather trades, more particularly in respect of greater production, caused a bigger supply of raw material for skin gelatine, and the slaughter of home animals for food caused a more plentiful supply of bones. At the same time it was realized that greater production not only reduced working costs, but also that a bigger turnover in any one factory involved a proportionately less capital outlay. These facts tend to counterbalance the heavy freight on the raw materials. Production is thus not only on a larger scale but more intensive. One of the greatest difficulties of this industry is to produce a regular or standard article, for the raw material is so exceedingly variable in quality; that for skin gelatine tends also to become less valuable. In such a case, as Rideal has truly remarked, to ensure that supplies to customers shall be always "up to sample," which is often a matter of contract--"exact and regular working, strict cleanliness, observance of temperatures and other physical data, and scientific supervision", are clearly necessary. "Rule of thumb" is never quite certain to produce the same article twice. In past years British methods of manufacture have been far too empirical. As in other industries, "rule of thumb" must inevitably be replaced by scientific principle. The advances in colloid chemistry of this last decade or so have, in the author's opinion, supplied the clue to this line of development. In the preceding pages emphasis has been laid upon the importance of the adsorption law, the lyotrope series, and the valency rule. The manufacturer or supervisor who understands and can apply these generalizations will find his task vastly easier and his factory more efficient. Much remains to be learnt, however, and the industry would certainly benefit by research work, for which there is a fertile field.