Phosphatic Materials used for Agricultural Purposes. 31 



paratively speaking little importance to the manufacturer of 

 artificial manures. But the fact pointed out in my analyses, 

 I believe for the first time, that there is in bone-ash, and of course 

 also in bones themselves and in bone-black, a considerable 

 excess of lime over and above the lime in the phosphate and the 

 carbonate, will explain why a larger proportion of oil of vitriol 

 must be used for producing a certain amount of soluble phosphate 

 from bone-ash than appears to be necessary according to pre- 

 vailing theory. 



The theory of the formation of soluble phosphate from insoluble 

 bone-earth has been perfectly well known some years ; it is not 

 affected by apparent discrepancies between so-called theoretical 

 calculations and actual practice. In the case before us the simple 

 fact is, that in all the analyses of bone-materials a considerable 

 quantity of lime has been overlooked or been supposed to be 

 united with phosphoric acid. As this excess of lime, which I 

 have pointed out as existing in all bone-materials, takes up sul- 

 phuric acid when such material is employed for making soluble 

 phosphate, more acid is required than has hitherto been supposed. 

 It is a common complaint of manufacturers of superphosphate, 

 that the materials which they use do not produce the quantity 

 of soluble phosphate which they ought to yield. There is, how- 

 ever, nothing surprising in this complaint, for it originates in a 

 proceeding that rests on calculations in which altogether erro- 

 neous data are employed. Instead of 77 per cent, of phosphate of 

 lime, as supposed, the bone-ash employed in all probability 

 only contains 73 per cent. ; and instead of 2 or 3 per cent, of 

 carbonate of lime, there is an additional quantity of lime, equal 

 to 5 to 8 per cent, of carbonate of lime, to be saturated before 

 any soluble phosphate can be produced. 



10. ANIMAL CHARCOAL (BONE-BLACK). 



The animal charcoal or bone-black which is used by sugar- 

 boilers for decolourizing crude sugar is far too valuable a material 

 to be used for agricultural purposes. When it has served for 

 some considerable time as a decolourizing agent it loses its 

 effect, and then is revivified by heating in cylinders. This re- 

 vivifying process is repeated many times, until most of the 

 carbon in the black is burned off; it is then sold to manure- 

 manufacturers as a refuse material, under the name of animal 

 charcoal. Like all refuse materials, its composition varies 

 greatly. Some samples are very rich in phosphates, others poor. 

 The amount of sand is usually very small ; in some samples 

 I have found a large proportion of carbonate of lime. 



