IO PRINCIPLES OF AGRICULTURAL CHEMISTRY 



ing acid phosphate by treating phosphate rock with sulphuric 

 acid. The process, which was patented, became the foundation 

 of the fertilizer industry. The Rothamsted experiments, prob- 

 ably the most famous field experiments yet instituted, have been 

 carried on with the same applications of fertilizers and manure 

 since 1852. Sir John Lawes endowed the Rothamsted Ex- 

 periment Station, and made provision for continuing its work 

 indefinitely. The great fertilizer industries, and the era of 

 agricultural experimentation, may be said to date from the ap- 

 plication of chemistry to agriculture made by von Liebig in 1840. 



Evidence for the Mineral Theory. As evidence that the organic 

 matter of the soil is not necessary to plants, plants have been 

 grown to full maturity in soils from which all the organic mat- 

 ter had been burned out. Plants were also grown in pure water 

 containing no organic matter, or carbon, to which certain mineral 

 salts had been added. A prize was offered by the University of 

 Gottingen for the solution of the question, whether the ash of 

 plants was taken from the soil or created by them. Such prizes 

 are still offered in Europe. This prize was won by Weigmann 

 and Polstorff. 1 In their first series of experiments, they grew a 

 number of plants of different kinds, upon sand from which the 

 soluble materials had been removed, as far as possible, by extrac- 

 tion with strong acids. One set of plants received only distilled 

 water, the other set received a mixture of the mineral salts found in 

 the ash of plants, and nitrates. The plants which received distilled 

 water hardly grew at all, but the others grew well. This was 

 evidence that the mineral matter was necessary for the growth 

 of the plants. The plants grown on the sand with distilled water 

 alone, when burned, were found to contain slightly more ash than 

 was present in the same quantity of seed from which they were 

 grown. Weigmann and Polstorff thought that this gain came 

 from the sand. They accordingly instituted further experi- 

 ments and grew plants in a platinum dish on platinum scraps 

 with distilled water, the seed being weighed. Upon incineration, 

 the quantity of ash in the plants was found to be exactly equal to 

 1 Dissertation, 1842, cited Meyer's Agricultur Chemie. 



