Glue, gelatine, animal charcoal, phosphorous, cements, pastes and mucilages

by F. Dawidowsky

4. The refining and purifying the phosphorus.

Burning the bones to ash. The object of the ignition of the bones is the complete destruction of the organic matter. The operation is conducted in a kiln very similar to those in use for burning lime. A layer of brush-wood having been put on the bottom of the kiln, bones form the next stratum, and so on alternately. The wood having been lighted, the combustion of the bones ensues. In order to carry off the fumes, the smell of which is very offensive, a hood made of boiler-plate is placed on the kiln, and either connected with a tall chimney, or the smoke and gases are conducted into the fire of the kiln and burnt. The white burnt bones are withdrawn through an opening reserved in the wall on purpose, the kiln being kept continuously in operation, as in the case with some lime kilns.

This kind of kiln, however, possesses many disadvantages, and an improved form, as proposed by Fleck, is shown in Fig. 50.

Fig. 50.

The actual combustion chamber consists of a shaft, A, composed of two inverted cones. In the lowest portion of the lower cone are four or six apertures, b, which terminate in inclined channels and serve as air-flues, as well as for withdrawing the burnt bones. Through the aperture a in the upper portion of the shaft additional bones may be introduced. This aperture is covered with a heavy iron lid.

As will be seen from the illustration, the shaft contracts towards the top in the form of a retort and passes into a horizontal channel B which is provided, near its beginning, with an ordinary fire-place d. The gases and fumes escaping from the burning bones must pass over the flame of the fire-place d, and are thereby so completely consumed to water, carbonic acid and free nitrogen that no odor is perceptible even in the immediate neighborhood of the kiln.

In order not to lose the heat yielded by the fire-place d and the burning vapors, the channel B is covered with shallow pans P, for the evaporation of such fluids as have to be subjected to this treatment in the factory.

The mode of operation with a kiln of this construction is as follows: The shaft is filled two-thirds full with bones and dry wood split in small pieces is placed in the channels b and simultaneously ignited. Four or six long hot flames thus strike the bones, the latter becoming in a short time so highly heated that they commence to burn briskly and ignite fresh portions of bones introduced through the aperture a.

The white burnt bones in the lower portion of the kiln are withdrawn, while in a glowing state, by means of iron hooks; the next layer of bones sinks down and fresh material is introduced through a, the kiln being thus kept continuously in operation.