BIOriKAIMUCAl, INTKODrCTroX 



xxm 



experiments in pots with agricultural plants, the manures made 

 use of supplying various elements of plant food. These cxpci-i- 

 ments were continued on a larger scale in 1^:N .md l^:;i». 

 Spent animal charcoal was then a waste product , and Mr 

 Lawes was asked by a London friend if it coulil I»e turned tu 

 any use. He therefore employed it as a mannre in his pot 

 experiments, and discovered that if previously treate<l witli 

 sulphuric acid its efficacy as a manure was greatly increased. 

 -Vpatite and other mineral phosphates were soon treatecl in a 

 similar manner, and the "superphosphate of lime," thus 

 prepared, was found to be most effective as a manure, especially 

 for turnips. The new superphosphate was employed on a 

 large scale for crops on the Eothamsted farm in ls4() and 

 1841, and the results were so satisfactory that in ls4*2 Mr 

 Lawes took out a patent for the manufacture of super- 

 phosphate. 



The application of sulphuric acid to bones had been 

 practised before the date of Mr Lawes' patent ; the novelty of 

 his patented invention consisted in the treatment of mineral 

 phosphates in this manner. The supply of lione available for 

 farmers is but small, but the supply of apatite, coprolite, and 

 of the various rock phosphates discovered in recent years, is 

 almost unHmited. These mineral phosphates are usually too 

 insoluble to have any practical value as manure, but by treat- 

 ment with a limited quantity of sulphuric acid, a mixture of 

 monocalcic phosphate, phosphoric acid, and gypsum is produced. 

 The phosphates in this compound are almost entirely soluble 

 in water, and far more efficacious as manure than the phos- 

 phates of raw bone. The enormous influence which the 

 introduction of superphosphate has had on the development of 

 agriculture may be gathered from the (juantity now aininall\ 

 employed by farmers. The annual mamifaclure of >nper 

 phosphate in Great Britain amounts at present to about 

 1,000,000 tons, while the total manufacture in the world is 

 about six times this amount. If Sir John Lawes had done 

 nothing more than introduce the manufacture of artificial 



