HOW BONEBLACK IS MADR. 143 
The boneblack should be reduced to fragments of con- 
siderably less than half the size of those of refiner’s bone- 
black, varying between 0°05 and 0°1 of an inch. The 
depth of the stratum in the filter drawer need not exceed 
6 to 8 inches; the density of the syrup should not exceed 
15° to 18° Beaumé’s saccharometer, and it should always be 
passed through hot. The rapidity and perfection of the 
filtration is secured by the position of the filter immediately 
over a boiling bed of syrup, where it is enveloped in an 
atmosphere of steam, by which contact with currents of 
cold air is prevented, and it is kept continually at a uniform 
degree of heat, receiving the boiling syrup from the pan 
above. 
This system of refining simultaneously with the evapora- 
tion is advantageous in several important particulars. It 
saves time; the syrup is passed directly from one compart- 
ment of the evaporator to the other through the filter. It 
effects more easily the separation of the impurities than if 
they had been suffered to remain and form new compounds 
at higher temperatures. The sugar also is then more 
readily crystallizable, is of better quality, and may be pro- 
duced in larger quantity than after reboiling at any subse- 
quent time. : 
The bone-charcoal should be prepared from large and 
solid beef-bones, carefully burned, according to the usual 
method, as already described. It should be neither of an 
ashy-gray color, nor lustrous black as if glazed, but of a 
deep dull black, and destitute of both odor and taste. 
When it has been exposed to too high a heat, it becomes 
glossy and is partially fused, and when allowed too free 
access to the air while burning, or while being cooled, 
much of the carbon is consumed, and in either case it is com- 
paratively inefficient. When not exposed to the proper heat, 
for a sufficient length of time, a part of the substance of the 
