110 THE CHINESE SUGAR CANE. 
the open end of the cotton bag being all “ puckered up,” 
is tied on to a brass tube, which, being fitted with a 
screw, is screwed into a small shallow cast iron or 
wooden tank, large enough to contain twenty-five to 
fifty of these brass tubes; the tank, besides serving to 
hang the filters, (which hang like so many sausages,) 
serves to contain the syrup which is to pass through the 
tubes into the bags, through which it percolates, and 
emerges clear and bright, free from feculencies and ex- 
traneous matters, and ready for the carbon filters. 
BONE BLACK FILTERS. 
These latter are large square or circular sheet iron 
tanks, which should be at least five feet in diameter, and 
six or eight feet deep. These have a false bottom per- 
forated with holes; over this a blanket is laid, and the 
tank filled up evenly with animal charcoal or bone black. 
A small air-tube generally runs from beneath the false 
bottom to the top. Over the top of the bone black the 
bag-filtered liquor is permitted to flow, which soon filters 
down through the false bottom; the cock of the filter is 
then opened, and the first running kept apart, being 
black and smutty from the small particles of charcoal 
dust which it contains. This is thrown on again at the 
top to be refiltered. The stream, however, soon runs 
clear, and, according to the length of time the syrup is 
left in contact with the bone black, does the decoloriza- 
tion sought for take place. If the stream be kept small 
the liquor may be drawn off colorless as water, and so 
