1HE CHEMISTRY OF THK SOIL. 



97 



It is applied usually at the rate of \ to 2 cwt. per acre, the amount varying 

 with the nature of the soil and with the quantities of the other manures 

 used iii conjunction with it. It is of especial value in the case of wheat 

 and root crops, audit forms the basis of the "general" manures, special 

 manures, mixed fertilisers, etc., on the market, such manures being usually 

 prepared from superphosphates by mixing it with sulphate of ammonia or 

 nitrate of soda and potash salts. 



Superphosphate obtained from mineral phosphate contains no nitrogen ; 

 that obtained from bones usually contains 2 or 3 per cent., a portion of the 

 tiitrogen having been lost in the process of manufacture. 



The following table will serve to convey an idea of the result of the action 

 •of sulphuric acid upon mineral phosphates and upon bone-meal respectively: — 



The tendency to revert is greater in those superphosphates which contain 

 iron and alumina, and in such manures a portion of the soluble phosphoric 

 -acid often reverts to the citrate-soluble condition on keeping for a length of 

 time. 



Dissolved bones is the name applied to superphosphate prepared from bones. 



Dissolved guano is superphosphate obtained from guano. 



Fish guano is not a guano, but fish offal. 



Thomas' phosphate, or Basic slag, must also be mentioned amongst phos- 

 •phatic fertilisers. It is a waste product of the manufacture of steel by the 

 Thomas-Gilchrist, or basic process, and contains, in the form of a phosphate 

 •of lime, the phosphorus existing in the original impure pig-iron. In Germany 

 and England enormous quantities have been consumed, it having proved 

 a very valuable and cheap form of phosphoric acid. Its great weight and 

 the consequent cost of transport has, no doubt, prevented its economical use 

 in this country. Recent changes in the steel-making processes, however, 

 are affecting the supply, and European farmers are likely to be dependent 

 on slags of rather less uniform and somewhat inferior qualities. 



Manufacture of Superphosphate on a Small Scale. 



The following directions for making this invaluable fertiliser on a smaii 

 scale may prove useful on farms where bones accumulate, and the question 

 arises how to deal with them most economically. 



It will be found most satisfactory in the first instance to burn the bones, 

 and convert them into what is known as bone-ash, since fresh bones or bone- 

 meal produce, on treatment with acid, a slimy mass, which is exceedingly 

 difficult to dry. 



t 54797 I) 



