From the time the weak sol is decolorized and bleached, the finishing processes consist essentially in the removal of water. This is now usually done partly by evaporation of the sol, and partly by the desiccation of the gel. There is an obvious elasticity in method, and factory practice does actually vary considerably in the relative proportions of these two alternatives. Some factories evaporate to a 20 per cent. sol, approximately, and rely upon drying sheds and lofts to complete the desiccation: other factories evaporate up to a 55 per cent. gelatine sol, and so can manage with less shed room. Something depends upon local conditions, but the main issue is between the cost of steam in evaporation and the cost of land and buildings required for sheds. On the whole the modern tendency is to evaporate more, for this course has the additional advantage of speed, involving both a quicker turnover and less liability of putrefaction. Lower-grade products need relatively greater evaporation to form a gel of equal rigidity. After evaporation and bleaching, the concentrated sol is first cooled rapidly until it has set to a stiff gel, then cut up into cakes according to the size required, these being dried out on network frames arranged in tiers, through which a draught of air is usually forced or induced. This general description is of course applicable to many factories with innumerable variations in detail, most of which variations originate in local convenience and are unessential parts of the manufacture. An essential principle is that the cooling or gelation should be done rapidly, not only to avoid putrefaction but also to avoid the action of heat on the elasticity of the gel. A hot sol or gel is liable to hydrolysis and loss of setting power, and should have its temperature quickly reduced, but a warm sol or gel (say 100° F.) is most liable to putrefaction, so that the cooling should be continued quickly. On the other hand, the gel should not be frozen. For cooling purposes a copious supply of cold water is most usually employed, but some factories have installed refrigerators. These plants operate by the rapid evaporation of liquefied gases such as carbon dioxide, sulphur dioxide, or ammonia, so arranged as to cool a solution of common salt, which forms the circulating liquor and is returned after use to the refrigerator. Where such plants are used, it is natural that their use should be extended to the drying sheds to cool the air entering in the height of summer. In some factories the cooling is attained neither by cold water nor cooled brine, but merely by cold air.