IV.] SUPERPHOSPHATE 119 



Superphosphate. 



In the early years of the nineteenth century, long 

 prior to the introduction of superphosphate as a 

 manure, the existence of a soluble phosphate of lime 

 produced by the action of sulphuric acid upon bone ash 

 was a matter of common chemical knowledge, and the 

 composition of this and the other phosphates had been 

 studied accurately by Berzelius. The application of 

 this knowledge to agriculture and the introduction of 

 superphosphate as an artificial manure began about 

 1840. The first published suggestion of the kind is 

 due to Liebig, in 1840, in his Report to the British 

 Association, which was published in the September 

 of that year as TJie Chemistry of Agriculture and 

 Physiology. Writing of bones as a manure and the 

 necessity of their being finely divided, he goes on : — 

 " The most easy and practical mode of effecting their 

 division is to pour over the bones, in a state of fine 

 powder, half of their weight of sulphuric acid, diluted 

 with three or four parts of water ; and after they have 

 been digested for some time to add 100 parts of water, 

 and sprinkle this mixture over the field before the 

 plough. In a few seconds the free acids unite with the 

 bases contained in the earth, and a neutral salt is 

 formed in a very fine state of division. Experiments 

 instituted on a soil formed from a Grauwacke, for the 

 purpose of ascertaining the action of manures thus 

 prepared, have distinctly shown that neither corn nor 

 kitchen garden plants suffer injurious effects in conse- 

 quence, but that, on the contrary, they thrive with much 

 more vigour." Liebig then adds : — " In the manu- 

 factories of glue, many hundred tons of a solution of 

 phosphates in muriatic acid are yearly thrown away as 

 being useless. ... It would be important to examine 



