144 ANIMAL CARBON, OR BONEBLACK. 
bones is not charred at all, and it proves ruinous to the 
syrup by communicating to it the peculiarly offensive flavor 
and odor of the animal oil and empyreumatic matter, 
which has not been driven off. This flavor and odor cannot 
be afterward removed from the syrup by any means known. - 
In burning boneblack a low red heat, prolonged for about six 
hours, in the ordinary covered iron pots, is productive of 
the best results, and no difficulty whatever need be appre- 
hended when the covers of the pots are luted with clay, or 
when pairs of pots are used fitting closely together, mouth 
to mouth, or when the bones are calcined in retorts. 
The powers of the boneblack become exhausted by use, 
and as has been mentioned, it is necessary to replenish the 
filter daily. But little loss of the material is thus incurred, 
however, for its energy may be restored by reburning, and 
this process of successive exhaustion and revivification may 
be repeated indefinitely, if the very fine particles or dust, 
amounting to but a small percentage of the whole mass, be 
sifted out each time after reburning, and enough of fresh 
carbon be added to supply its place. In order that its 
action may not be impaired, the boneblack should always 
be washed free from sugar before reburning it. (See Ch. 
aN T,) 
The revivification of the carbon is accomplished econom- 
ically on the large scale in different ways. It may be ex- 
posed to a red heat in cast-iron retorts of a conical shape, 
placed vertically over openings in a bed-plate in a furnace. 
Through these openings the boneblack is discharged, when 
red hot, by drawing a slide, and through similar apertures 
in the tops of the retorts, they are refilled. Or it may be 
placed in a cylinder, and steam, heated to 700° or 750° F., 
driven through it. It may also be reburnt in the iron pots 
above mentioned, with success. Large retorts are some- 
times made of fire-bricks, of the shape of a square hollow 
