41G 



BONE-BLACK 



furnished abundant materials for making the most satisfactory experiments, and enabled 

 till-so gontlomon soon to obtain ton per coiit. more of refined sugar from the raw 

 article than had been formerly extracted, and to improve, at the time, the characters 

 of the lumps, bastards, treacle, &c. 



The calcination of bones is effected by two different systems of apparatus; by 

 heating them in a retort similar to that in which coal is decomposed in the gas-works, 

 or in small pots piled up in a kiln. On the second plan, which furnishes the best 

 charcoal, the bones, broken into pieces, are put into small cast-iron pots of the form 

 shown in Jig, 148, about three-eighths of an inch thick, two of which are dexterously 

 placed with their mouths in contact, and then luted together with loam. The lip 

 of the upper pot is made to slip inside the under one. These double vessels, con- 

 taining together about fifty pounds of bones, are arranged alongside, and over each 

 other, in an oven like a potter's kiln, till it is filled. The oven or kiln may be either 

 oblong or upright. The latter is represented in figs. 149, 150, 151. A is the fire- 

 place or grate for the fuel ; c c are the openings in the dome of the furnace through 

 which the flame flows; the divisions of these orifices are shown \nfig. 151. B is the 

 wall of brick-work. D the space in which the pots are distributed. E is the door 

 by which the workman carries in the pots, which is afterwards built up with fire- 

 bricks, and plastered over with loam. This door is seen in fig. 149. F F are the 

 lateral flues for conveying the disengaged gases into the air. 



152 



Fig. 152 is a longitudinal section, and fig. 153 a ground plan of a horizontal kiln 

 for calcining bones, a is the fire-chamber, lying upon a level with the solo of the 

 kiln ; it is separated by a pillar b, from the calcining hearth c. In the pillar or wall, 

 several rows of holes, d, are left at different heights ; e is the entrance door ; /, the 

 outlet-vents for the gases, vapours, and smoke, into the chimney g ; h, a sliding 

 damper-plate for regulating the admission of the air into the fire in the space a. 



By this arrangement the offensive emanations are partly consumed, and partly car- 

 ried off with the smoke. To destroy the smell completely, the smoke should be made 

 to pass through a second small furnace. 



The number of pots that may be put into a kiln of this kind depends, of course, 

 upon its dimensions; but, in general, from 100 to 150 are piled up over each other, in 

 columns, at once ; the greatest heat being nearest the roof of the kiln, which resembles, 

 in many respects, that used for baking potteryware. 



In both kilns the interior walls are built of fire-bricks. In the oblong one, the 

 fiercest heat is near the vaulted roof ; in the upright one, near the sole ; and the pots, 

 containing the larger lumps of bones, should be placed accordingly near the top of the 

 former and the bottom of the latter. Such a kiln may receive about seventy double 

 pots, containing in the whole thirty-five cwts. of bones. 



After the hearth is filled with the pots, and the entrance door is shut, the fire is 

 applied, at first moderately, but afterwards it must be raised, and maintained at a brisk 

 heat for eight or ten hours. The door of the ash-pit and the damper may now be 

 nearly closed, to moderate the draught, and to keep up a steady ignition for six or 

 eight hours longer, without additional firing; after which the doors must bo all 

 opened to cool the furnace. When this is done, the brickwork of the entrance-door 

 must be taken down, the kiln must be emptied, and immediately filled again with a 

 set of pots previously filled with bones, and luted together: the pots which have 

 been ignited may, in the course of a short time, bo opened, and the contents put into 

 the magazine. But in operating with the largo decomposing cylinder retort, the 

 bones being raked out hot, must bo instantly tossed into a receiver, which can be 

 covered in air-tight till they are cool. 



