SUPERPHOSPHATE OF LIME. 



169 



it as forty-five per cent. The above, however, may be con- 

 sidered as a fail- averag-e in the state usually employed by 

 farmers. 



Four bushels of bones, which may be considered to be a 

 fair allowance for an acre, will weig'h, in a fine state of bone- 

 dust, about 180 lb. ^ This cpiantity contains 12|- lb. of 

 carbonate of lime, consisting- of carbonic acid, 5|- parts, and 

 lime, 7 parts, which will require 10 lb. of sulphuric acid to 

 convert it into sulphate of lime or gy[)sum. This is the 

 first result of tlie mixture, and is the cause of the very 

 impleasant fumes which are given ofi", and which consist, in 

 fact, principally of carbonic acid diseng-ag-ed from the car- 

 bonate of lime, in consequence of the superior affinity which 

 lime has for sulphuric acid. This result takes place before 

 the acid acts on the phosphates of the bones, and tlius it is 

 that when a small quantity of acid has been sprinkled over 

 bone-dust, the good effect has been but moderate, the car- 

 bonate of lime alone has been acted on, and the phos})hate 

 of lime has remained undecomposed. 



The quantity of phosphate of lime existing- in the 4 bushels 

 of bones, is about 106 lb., containing- 47 lb. of lime, and 

 69 lb. of phosphoric acid. If we consider superphosphate 

 of lime to contain a double portion of acid — a fact, however, 

 not quite decided — then 33 lb. of sulphuric acid will be 

 required, which, by uniting- with half the lime, or 23^ lb., 

 forms g-ypsum, and leaves the other moiety of lime united 

 "with a double jiortion of |)hosphoric acid in a state of su])er- 

 phosphate. Thus, 43 lb. of acid will be required to effect 

 these chang-es, leaving- any additional quantity for other pur- 

 poses. ^ 



Phosphate of lime is a substance very difficult of solution, 

 and thus, in a very dr}- season, the effects of bones are often 

 very slig-ht and imperfect. Superphosphate of lime, on the 

 other hand, is extremely soluble, so much so that the 

 vitriolized bones can be entirely dissolved or suspended in 

 Avater, and thus applied. This at once explains the cause of 

 the valuable properties of the preparation. The bones in 



' I find that the average weight of bone-dust, as it comes from the 

 mill, is 1G8 lb. per 4 bushels, although I have found it reach the weight 

 stated in the text. — Author. 



^ I do not mean to say that these are the precise changes which take 

 place, but only an approximation to them. Probably, some portion of 

 phosphoric acid may be left in a free state in the prepared mixture. 



