As will be readily understood this process consumes much fuel, and leaves a residue which, though not completely exhausted, cannot be further utilized for the preparation of gelatine. In fact the entire process is obsolete, but as it is still in use in some localities, a description is here given, for the sake of completeness, of the apparatus and improved manner of manufacture employed in the factory of D. J. Briers, which is well known for the beautiful product turned out.
Fig. 59 shows a longitudinal section of the entire apparatus.
Fig. 60 is the horizontal section of the boiler.
a, is the cylindrical boiler 6 meters (19.68 feet) long, and 2 meters (6.56 feet) in diameter. It is made of strong boiler plate doubly riveted, and capable of resisting a pressure of six or seven atmospheres.
b, is the manhole. It is closed by an oval lid secured by two iron rods and two bolts, so that after placing the lid in position, the boiler is hermetically closed by tightening the nuts upon the bolts.
c, is a cast-iron fork with two safety valves with levers graduated from 1 to 100 atmospheric degrees.
Fig. 60.
d, is a float upon the surface of the water, and provided with a wheel graduated from Nos. 1 to 6. Its object is to indicate during the operation how much water is lost and how much remains in the boiler. Care must be had not to allow the indicator of the wheel to get below No. 1. This figure indicates that the water has reached the highest point in the boiler exposed to the fire, which is consequently the lowest point which the water can be allowed to reach. On the other hand the indicator must not move above No. 6, as the water when standing too high in the boiler and too close to the pipes conducting the steam into the various apparatuses might mix with the steam and spoil the operation carried on in the drum, e, Fig. 60.