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´.
Fig. 64.
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.
To change the position of the bones, the drum is revolved twice every half hour, by means of the gearing q, of course closing the cock x during the operation.
By carefully following the above rules, the bones will be thoroughly reduced in four hours. If, for instance, steam has been introduced into the drum at 5 o’clock a. m. the operation will be finished at 9 a. m. The cock y, is then closed, and the steam allowed to escape through the cock x. After the escape of the steam, the drum is emptied, by removing the lid and turning it upside down. It is then refilled with entirely dry bones, and the operation continued in a like manner, day and night, if necessary.
After the bones have been taken from the drum, they are spread out under a shed, and, when dry, ground in a suitable mill. The resulting flour, which contains the jelly-yielding substance, is brought into the vessel d´, which, in the meanwhile, has been furnished with sufficient water to cover the flour 65 centimeters (25.59 inches) deep. The mixture is boiled for three-quarters of an hour, being constantly stirred to prevent the flour from forming a heavy and dense mass which would hinder the quick extraction of the jelly. Ebullition is then interrupted by closing the cock h, and the fat floating on the surface skimmed off. After allowing the gelatinous solution to settle, it is drawn off by means of a faucet placed above the level of the flour. Thirty bucketfuls of the gelatinous solution are then at once poured into a vat and mixed with the condensed steam drawn off by means of the cocks t u, during the reduction of the bones in the drum. After allowing the mixture to cool to 160° to 155° F., 20 kilogr. (44 lbs.) of pulverized alum are added at once and as quickly as possible. When the gelatinous solution has become transparent, it is drawn off into the box e´, and a few bucketfuls of hot water are poured upon the sediment in the vat in order to extract the remaining jelly, which is effected by thorough stirring and allowing to settle until the water is entirely clear.