There is also considerable room for improvement in the methods of chemical engineering usually employed. Whilst the heat engineers have certainly done much to solve the question of evaporation and drying, there is still great scope in the more economical application of heat in extraction, and the last word can hardly have been said on the problem of clarification and decolorization. There is indeed almost as much scope for research by the chemical engineer as by the colloid chemist. The industry also exhibits, in common with the leather and many other trades, the same tendency to save labour, both by careful arrangement of the factory and by the installing of mechanical labour-saving devices. Thus, lifts, runways, hoists, and trucks are increasingly used to move the solids, and pipes and pumps to move the liquors. As ever, there is scope for the mechanical engineer. If some of these problems are vigorously tackled during the present reconstruction period, there is little doubt that the gelatine and glue industry will be in a much better position to cope with all possible competition in the future. From what has been said in Section VIII. as to the wide uses of gelatine and glue, it will be seen that general prosperity in trade is conducive to better trade conditions in the gelatine and glue industry. It is similarly true that a general trade slump affects the glue trade adversely. The severe trade depression which commenced in 1920 has had this effect, and has made economic production much more difficult as well as more essential. As often is the case, the larger factories and firms can better face the difficulties, and there can be little doubt that if the depression be long continued there will be a tendency for the smaller factories to be closed down and for the larger firms to unite. As in the leather trade, both the War boom and the Peace slump have caused the gelatine and glue trade to develop along the lines of the great trusts. It may be reasonably expected, moreover, that these will be intimately connected with the leather trusts. This fact, together with the heavy freight charges on the raw material, tends also to make the skin glue factories gravitate towards the leather centres. PART VI.--MISCELLANEOUS PROTEINS AND BYE-PRODUCTS SECTION I.--BYE-PRODUCTS OF THE LEATHER TRADES