_p´_, Fig. 62, is a cock in the bottom of the box _d´_ for drawing off the gelatinous solution from the residue. The box _e´_, Fig. 62, a ground-plan of which is shown in Fig. 63, serves for evaporating the gelatinous solution, which is effected by circulating steam through several tubular pieces of cast-iron which form the bottom of the box and are connected in a similar manner as the pipes in the box _d´_.
The cock _i_ is graduated and similar to _h´_.
The cock _r´_, Fig. 63, is similar to _o´_, Figs. 59 and 62.
_s´_, Fig. 63, is a cock for drawing off the evaporated gelatinous solution.
The wooden box _f´_, Fig. 59, a ground-plan of which is shown in Fig. 64, serves for the reception and settling of the evaporated gelatinous solution. Its bottom is constructed in a manner similar to that of the box _e´_.
The cock _n´_, which is placed 14 millimeters (0.55 inch) above the bottom of the box, serves for running the gelatinous solution into the wooden cooling-boxes.
The bones as received in the factory are sorted by throwing out the spongy material, etc. They are then steeped in lime-water for a few days to free them from adhering particles of flesh, after which they are dried and stored away for future use.
The boiler _a_, is filled two-thirds with water, and heated until the manometer indicates a pressure of 30°. In the meanwhile the drum _e_, is filled seven-eighths with perfectly dry bones, and steam is then admitted from the boiler _a_, through the graduated cock _y_. The fact that the bones in the drum are exposed to the proper temperature of 250° F. is recognized by the thermometer _b´_, placed between the cock and the drum.
To prevent the stagnation of the steam in the drum, _a_ small jet of it is allowed constantly during the operation to escape through the cock _x_. The cock must not be opened wider than is necessary to keep the temperature at 250° F. By opening it wider, this degree would be exceeded, and the gelatine-yielding substance would, in consequence, undergo alteration. A quarter of an hour after admitting the steam into the drum, the cock _t_, is opened, and again closed after allowing a small portion of the condensed steam to escape to the cock _u_, and, through this, into a box. This operation is repeated every quarter of an hour.