The kind of vessel in which gelation is induced varies widely in different factories. For lower-grade products metal boxes are used, heavily galvanized iron being the most common material. If the liquor be muddy, deep boxes are preferred, but if clear, rapid cooling is best attained by having them long and shallow, and so exposing a relatively greater area to the cooling action. In either case the boxes may contain up to 1/2 cwt. of jelly. Lambert mentions boxes 24" × 6", which are 5" deep; Cavalier suggests rectangular moulds holding 30 litres. In place of galvanized sheet iron, boxes of sheet zinc or of wood lined with zinc are sometimes used. In any case the most scrupulous cleanliness should be observed in all cooling-house work, and in some factories the most elaborate precautions are taken for cleansing vessels, tools, floors, etc., and even for their disinfection and sterilization. Iron, tinned iron, and copper cooling vessels are ruled out on account of their tendency to rust and tarnish, and the last is unjustifiably expensive. Many of these vessels are unsuitable for pure food gelatines in which traces of copper, zinc and arsenic are held to be very objectionable. For the best gelatines, therefore, a very shallow vessel (1/4" to 1/2" deep) with a sheet glass bottom is preferred, and the concentrated sol is run on to this for gelation. Glue (or gelatine) which has set in this way is sometimes called "cast glue." That which sets in metal boxes in blocks is termed "cut glue," because the blocks of jelly need subsequently to be cut into slabs of the desired size and shape. Jelly blocks may be cut by hand with the "wire knife" which yields a characteristic wavy appearance to the finished product. This may also be done by machinery, the block of gel being placed on a series of correctly spaced wires and forced through the network by hydraulic pressure. A cutting machine (Schneible) has also been used to cut up blocks of jelly into slices of the required thickness, but these machines have not made great headway in this country. It will be clear that cast glue is cooled more rapidly than glue in blocks; it is therefore not surprising to note Lambert's statement that the former comprises the larger proportion on the market.