760 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



was noticed and valued, but later the main service, rendered by 

 the black, was found to be the absorbtion of alkalies, salts and 

 other substances, impeding the crystallization of sugar. In this 

 respect filtration is only a second defecation. .The boneblack 

 was first used in th€ powdered state, being boiled with the sugar- 

 juice. It then could be used but once. In 1828 Dumont intro- 

 duced the use of coarsely grained boneblack, which he used in 

 small filters. The action of a filter is increased with its heighth 

 in proportion to its diameter, for then every particle of liquor 

 passes through a greater amount of black, exhausting it more 

 thoroughly than when the diameter is greater in proportion to the 

 height ; hence the rule that filters should be at least ten times 

 as high as wide. 



The height of filters for the economical use of bone-black, in 

 quantities proportionate to the present scale of manufacture, 

 would render the use of filters necessary higher than sugar 

 refineries generally are. For this reason filter batteries are em- 

 ployed, i. e., a series of filters communicating with each other. 

 They are generally arranged in the following way: The empty 

 space between the grains of bone-black is sufiicient to hold fifty- 

 five to sixty per ct. of its weight. The amount of bone-black used is 

 twenty per cent of the weight of beets, or twenty-two per cent of 

 the weight of the juice. The filters are closed at the top to pre- 

 vent absorbtion of air, which might otherwise cause fermentation, 

 and of ammonia, which is always present in beet sugar refineries, 

 being produced by the action of lime on the protein substances at 

 the boiling point. Where water is plentifully supplied, it might 

 advantageously be used to cool the filter, to preserve the liquor at 

 a low degree of heat. 



Besides the shape of the filter, the quality of the bone-black is 

 of importance. It should alwaj^s be of a dull black, velvety 

 appearance, should adhere to the tongue, when brought in contact 

 with it, both of which are signs of great porosity. When the 

 filter is exhausted, the access of juice is shut ofi", and steam intro- 

 duced at the top, which condenses in the pores of the black, and 

 washes out whatever saccharine juice may remain in it. This 

 same process is also gone through with a few times before the 

 filter is used, whereby are removed all the salts from the black; 

 it then has an increased absorbtive power for the salts of the 

 liquor. On the whole, filtration is carried on in the same wa}' as 

 in our American refineries for tlie manufacture of cano-su2:<ii*- 



