MANUFACTUKE OF BONE SUPEEPHOSPHATE. 191 



acid of SO'' to 60" B., and the whole heated to boiling. The leather 

 rapidly dissolves to form a brovv'n liquid, which is drawn off by a 

 tap a little below the false bottom, and which is used in place of 

 ordinary sulphuric acid to dissolve the bones. This method of 

 treating leather presents great advantages. It enables the manu- 

 facturer to preserve all the nitrogen, which would otherwise be lost, 

 as extract. Besides, and it is an important point, the tannin 

 opposed to the decomposition of the leather in the soil is destroyed. 

 Flesh, lungs, livers, spoilt greaves and other waste are dissolved by 

 the acid like leather. The sequel of the treatment is the same as 

 in the case of leather. Greaves are particularly rich in nitrogen. 

 They often give up as much as 10 per cent of fat to the sulphuric 

 acid used to decompose them. If sulphate of ammonia be used to 

 increase the nitrogen content of dissolved bones, it likewise can be 

 dissolved in the sulphuric acid, whilst nitraie of soda can only be 

 added to the finished product. The mixing is then done by aid of the 

 crusher or by the toothed roller mill. Hair, horn, and wool waste 

 are also dissolved in the acid. The solubility of the organic matter 

 is greater in nitrous sulphuric acid than in sulphuric acid alone. For 

 one part of these materials, two parts of nitrous sulphuric acid at 

 50" to 60° B. are taken, and if there be no nitrous acid at disposal 

 residual sulphuric acid is supplied by an addition of 2 per cent of 

 nitrate of soda.^ 



Animal Charcoal. — Commercial animal charcoal comes almost 

 exclusively from sugar refiners and glucose factories. To purify their 

 juices, the refiners use large amounts of animal charcoal. In the new 

 state, that is to say, freshly calcined, the black possesses a very ener- 

 getic decolorizing power. But this property is attenuated by use. To 

 revivify the black, and to restore to it, at least partially, its decoloriz- 

 ing and purifying properties, it is fermented, treated by acids, 

 washed, then again calcined without access of air. Thus revivifying 

 operations give rise to an important waste under the form of a fine 

 powder, which is sold as manure. After a series of revivifications, 

 the granular black is itself spent, and revivification is powerless to 

 restore to it its initial properties. Formerly animal charcoal was 

 in current use in sugar works, but within the last fifteen years it 

 has completely disappeared. The refineries alone continue to use it, 

 and consequently it is not so important a manure as formerly. The 

 composition of this product is very variable, according to the 

 methods of manufacture of the sugar refineries. As the char dust 

 (revivification) waste comes always from the surface of the granules 

 of black, and as these parts are the most attacked by the hydro- 

 chloric acid used to purify it, it contains an important proportion 

 of carbon, but less phosphate of lime, than the granular black, 



1 See note 1, p. 188. 



