218 



On Superphosphate of Lime. 



heated in an open furnace, are reduced to a white ash. I do 

 not imao-ine that this is often done with the view of making 

 superphosphate from the products, as, whilst nitrogen and 

 ammonia have so high a value, it v;ould be a very unwise and 

 wasteful process ; but I am given to understand that the bones 

 of Vv'hales and other animals have been occasionally so burnt to 

 render them lighter and more portable and prevent the danger 

 arising from their heating in the holds of vessels in which they 

 are to be brought to this country. 



Bone-ash would contain on an average perhaps from 80 to 90 

 per cent, of phosphate, and from 8 to 12 per cent, of carbonate 

 of lime. Animal charcoal is prepared b}^ heating bones in close 

 iron vessels, such as gas-retorts. It is used very largely by the 

 sugar-refiners, and comes into the possession of the manure- 

 maker only when it has ceased to be of any service to the former. 

 When originally made, animal charcoal, or bone-black, contains a 

 considerable percentage of charcoal, but after it has been burned 

 over and over again, until it ceases to possess any discolouring 

 power for the syrups of the sugar-boiler, the proportion of char- 

 coal is very much reduced, and the phosphate proportionally 

 increased. I have found the waste animal charcoal to contain from 

 65 to 75 per cent, of phosphate of lime, with 10 or 12 per cent, 

 of carbonate, and about the same quantity of charcoal. But 

 both this and bone-ash vary very m.uch in quality, and in all 

 cases it is necessary to ascertain their composition by analysis 

 before employing them largely in the manufacture of superphos- 

 phate. They are seldom the basis of this manure, but only one 

 of the ingredients. 



Superphosphate of lime from coprolites. — The coprolites of the 

 crag formation are obtained abundantly and cheaply, and have 

 been extensively employed as a source of phosphoric acid in 

 the manufacture of the superpospbate. They are very hard, and 

 are only attacked with any energy by sulphuric acid after they 

 have been reduced to a fine powder. 



The following numbers will represent approximatively the com- 

 position of these fossils ; they are the results of an analysis m.ade 

 by me some time ago of a sample taken from a heap of the 

 powdered coprolite : — 



Water (of combination) and a little bituminous matter 10 

 Sand, clay, and oxide of iron . . . . .21 

 Carbonate of lime ....... 10 



Phosphate of lime , . 56 



Fluoride of calcium, with small portions of alkaline sul- 

 phates and chlorides . ..... 3 



100 



It is very possible that the composition of samples of ground 



