Bone Black Filters

The sirup after passing through the bone-black filter is in the state of maximum purity. The subsequent processes of the sugar-maker consist in the removal of the water. This is effected by evaporation ... 

The bone black filters used in decolorizing glucose are tall iron cylinders each having a capacity of from 16 to 20 tons of bone. There is a syrup inlet at the top and a syrup outlet at the bottom. However, the syrup outlet pipe is carried up the side of the filter until it reaches the level of the top of the bone on the inside of the filter. There is a manhole at the bottom for removal of spent bone. 

Dumont s filter consists of a wooden box of j he form of a four-aided truncated pyramid with a double bottom. The inner bottom is a metallic plate pierced with numerous holes upon it a cotton cloth is kid, and coarse-grained animal charcoal moistened with water is then Bpread layer by layer each layer being rendered of uniform thickness, and packed or pressed closely together by means of a sort of trowel. When the bone-black has been thus formed into a compact bed or stratum of about fifteen or eighteen inches in thickness, and Within five to ten inches fi om the top of the box, it is covered with another cotton cloth, and with another metallic plate pierced with holes, The object of the second cloth and metallic cover Is to collect any substances which would otherwise obstruct the interstices of tho superior stratnm. of the bone-black—an inconvenient accident which is easily prevented by the use of such a cover, and this cover is readily exchanged for another, should it be no mo itself obstructed. The superior covir is only of use when the previously described filtration through the cotton bag or leaf filter is omitted. 

The same bone-black maybe employed any number of times, provided the substances which it has withdrawn from tho sirup be. removed. This is sometimes done by allowing them to ferment, as in Peyros s filter but more frequently by simple rekihiirig. The kiln made. by G. -F. Chantrell of Liverpool for the revivification of the bone-black is seen in Fig. 558. Those of Pontifex and. Wood and others are under the article. Cftarcoal,... 

The employment of bone-black, also, resembles almost completely its use with cane sugar. In the beetroot sugar manufacture, however, tho filtering cylinders have usually a longer and narrower form than is the case with cane sugar. 

If the ether extracts are not thoroughly dry, the mercaptan appears slightly cloudy on subsequent distillation. The checkers found that this cloudiness was frequently due to colloidal sulfur. The sulfur can be removed by shaking an ether solution of the cloudy product with bone black, then filtering and distilling. 

Filter Aids.—Among these are calcium sulphate and carbonate, sawdust, flour, pulverized bone black, infusorial earth, etc. Where the amount of solids in the filtrate is small or where the solids arc of such nature that they readily pass through ordinary filter media resort may be had to a filter aid to coat the medium and to prevent the filtrate from issuing from the press as a cloudy fluid. Filter aids are also used to increase the brilliancy of the filtrate and to assist in filtering solids which are adsorbed more or less readily by them. In such cases the aid after having adsorbed the solids or colloids is run with its liquor into the press with the same slight degree of trouble that is had with easily filterable materials. 

Decolorization of Solutions.—If a substance contains tarry materials which impart to it a color it can be purified usually by boiling a solution of it for some time with bone-black, and filtering the hot solution. The efficiency of the process and the amount of bone-black required are markedly affected by the quality of the latter. As an approximation about 1 gram should be used for a solution of 250 cc. which is moderately colored. 

A precipitate of hydrazine sulfate (NH2NH2.H2S04) forms. The mixture is allowed to stand in the cold for a few hours in order to complete the precipitation, and is then filtered by suction in the usual way and washed with cold alcohol. The yield varies from 53 g. to 58 g. per 1500 cc. of ammonia water (34-37 per cent of the theoretical amount). The product is perfectly white and crystalline, and satisfactory for almost any purpose. If an absolutely pure product is desired, it must be recrystallized from water. For every 21 g. of crude product, 100 g. of boiling water are used. If the crude hydrazine is brown, it is advisable to use a little bone-black. After the mixture has been filtered and cooled to 0°, 19 g. of pure white crystals are obtained. 

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