HISTORICAL AND INTRODUCTORY 17 



tains a sufficient quantity of alkalis, phosphates, and sulphates, 

 nothing will be wanting. The plants will derive their 

 ammonia from the atmosphere as they do carbonic acid," he 

 writes in the Farmer s Magazine}- Ash analysis led him to 

 consider the turnip as one of the plants " which contain the 

 least amount of phosphates and therefore require the smallest 

 quantity for their development ". These and other practical 

 deductions were seized upon and shown to be erroneous by 

 Lawes (161-162) who had for some years been conducting 

 vegetation experiments. Lawes does not discuss the theory 

 as such, but tests the deductions Liebig himself draws and 

 finds them wrong. Further trouble was in store for Liebig ; 

 his patent manure when tried in practice had failed. This 

 was unfortunate, and the impression in England at any rate 

 was, in Philip Pusey's words : " The mineral theory, too 

 hastily adopted by Liebig, namely, that crops rise and fall in 

 direct proportion to the quantity of mineral substances present 

 in the soil, or to the addition or* abstraction of these sub- 

 stances which are added in the manure, has received its. 

 death-blow from the experiments of Mr Lawes ". 



And yet the failure of the patent manure was not entirely 

 the fault of the theory, but only affords further proof of the, 

 numerous pitfalls of the subject. The manure was sound in 

 that it contained potassium compounds and phosphates (it 

 ought, of course, to have contained nitrogen compounds), but 

 it was unfortunately rendered insoluble by fusion with lime 

 and calcium phosphate so that it should not too readily wash 

 out in the drainage water. Not till Way had shown in 1850 

 that soil precipitates soluble salts of ammonium , potassium and 

 phosphates was the futility of the fusion process discovered, 

 and Liebig saw the error he had made (\J^b). 



Meanwhile the great field experiments at Rothamsted had 

 been started by Lawes and Gilbert in 1 843. These experiments 

 were conducted on the same general lines as those begun 



1 Farmer's Magazine, 1847, vol. xvi., p. 511. A good summary of Liebig's 

 position is given in his Letters on Chemistry, 34th letter, 3rd edition, p. 5195, 

 1851. 



2 



