ACTION OF FILTERING MATERIAL. 141 
The filter used in this proces differs from the boneblack 
filters of the ordinary form in its shallowness, the compara- 
tively small quantity of the charcoal used, the fineness of 
division of its particles, and in some of its chemical 
properties. 
Ordinary boneblack, as used by the sugar refiners, is 
prepared by subjecting clean beef-bones in iron retorts, or 
covered pots in a furnace, to a red heat for some hours. 
An imperfect combustion of the bones takes place, access 
of air is prevented, all volatile substances which are pro- 
duced are driven off, and a dull black substance remains 
behind retaining the original form of the bones, consisting 
of phosphate of lime associated with a little carbonate of 
lime, sulphuret or oxide of iron, and silicated carburet of iron 
90 parts, carbon 10 parts. The charred bones are excluded 
from the air until cool, and then are broken up in a mill 
into small fragments, averaging 0:1 to 0°3 of an inch in 
diameter, and the finer particles are sifted out. This 
charcoal is exceedingly porous, and its superior decolor- 
izing power, as well as its chemical action, seems to depend 
upon the very great extent of surface presented by the 
carbon to the liquid with which it comes in contact. For 
the same reason the more finely divided its particles are 
the more effective it becomes. It is far more energetic in 
its action than most other forms of charcoal, besides pos- 
sessing other properties peculiar to itself. All these prop- 
erties, however, may be variously modified, by the mode 
in which it is prepared, and its particular form, to suit 
certain ends. 
The action of the filtering material used in this process 
embraces the following particulars: 
1. It removes the extractive matter which imparts to 
sorghum syrup its peculiar harsh flavor, and which resists 
the action of heat and all other means that have been used 
to effect its separation. 
