BIOGRAPHICAL INTRODUCTION xxiii 



between chemistry and agriculture. In 1837 he commenced 

 experiments in pots with agricultural plants, the manures made 

 use of supplying various elements of plant food. These experi- 

 ments were continued on a larger scale in 1838 and 1839. 

 Spent animal charcoal was then a waste product, and Mr 

 Lawes was asked by a London friend if it could be turned to 

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

 experiments, and discovered that if previously treated with 

 sulphuric acid its efficacy as a manure was greatly increased. 

 Apatite and other mineral phosphates were soon treated 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 Rothamsted farm in 1840 and 

 1841, and the results were so satisfactory that in 1842 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 bone available for 

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

 of the various rock phosphates discovered in recent years, is 

 almost unlimited. 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 quantity now annually 

 employed by farmers. The annual manufacture of super- 

 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 



