Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 186

In England the raw material, before being boiled, is limed; this treatment is not necessary in the case of hide cuttings from leather dressers and tanners, scrap from trotter-boilers, dry glue pieces and parchment cuttings, which are already limed. The liming is effected by soaking the material in milk of lime contained in pits. Afterwards it is necessary to remove or kill the lime by washing with water in vats or pits, or even in revolving drums. The lime in old glue pieces is killed sufficiently by the action of the atmospheric carbonic acid, the glue being spread out in trays so as to be more readily affected. In some works the washed materials are subjected to heavy pressure, but in others the boiling is proceeded with at once. The boilers or pans generally have each a capacity of several tons. A false bottom of bars keeps a clear space at the bottom. In the middle of the boiler is a removable vertical framework, and its object, like that of the false bottom, is partly to give free space, so that the boiling liquid can circulate thoroughly, and partly to simplify the straining of the liquid. The pans are heated by a fire beneath, by steam, or by the two together. In placing the materials in the pans, any horn “sloughs” that may be used are built up around the central framework, the rest of the material being then put in. During the boiling intermittent stirring is necessary, and the fat which rises to the surface has to be skimmed off. The charge for the pans is in the proportion of twelve tons of fleshings to one ton of water. On the completion of the boiling the fire is put out, or the heat is otherwise removed; a time is allowed for partial settling and cooling, and the liquid is then drawn off through a wooden channel from the space beneath the false bottom. In this wooden channel are lumps of alum, and the liquid glue is conducted to cooling troughs, where it is allowed to cool and harden into a jelly or size. The succeeding processes by which the size becomes glue resemble those practised in America and previously noted. The methods outlined above admit of many variations, nearly every manufacturer adopting a system that in some particular differs from that adopted by his fellows.

Fig. 478.—Defect of Old-fashioned Wood Screw.

Fig. 479.—American Improved Wood Screw.

Fig. 480.—Glue-pot and Brush.