432 History of the English Landed Interest. 



burning, liming, and pulverising both light and heavy soils. 

 He detected the presence of ammonia in the fermenting mat- 

 ter of the dung-heap, proved its great value as a fertiliser, and 

 thus induced the husbandman to give up the practice of rotting 

 his manure, whereby its preservation for practical uses had 

 hitherto been damaged,^ 



It remained for Liebig, in 1840, to replace the " liumic " 

 by the " mineral " theorj^, and thus to carry the farmer one 

 step further in the right direction. He rightly demonstrated 

 that before plants can thrive they must have access to both 

 organic and inorganic matter in a form in which it can be 

 assimilated, Regarding, however, the atmosphere and the soil 

 between them as the inexhaustible sources of all organic con- 

 stituents required bj^ the vegetable economy, he considered 

 himself free to direct his undivided attention to the best 

 means of suppl^^ing it with its inorganic wants, which, accord- 

 ing to his views, were alone liable to be exhausted. He 

 pointed out that though humus contains carbon, it must be 

 converted into carbonic acid before it can be assimilated by 

 plants ; and though, by the process of decomposition, it 

 furnishes a source of this gas, it does so in a far more 

 roundabout way than does the atmosphere, and therefore its 

 chief fertilising agencies are owing to its being a reservoir of 

 mineral foods. He applied the same reasoning to the virtues 

 of ammonia as a manure, asserting that it was not the 

 chemist's duty to waste time in seeking sources of expensive 

 nitrogenised foods for an impoverished crop, since nature her- 

 self afforded these by means of the atmosphere. He therefore 

 set to work in the laboratory to find out the proportions of 

 the mineral constituents in each plant, and then to synthesise 

 equivalent proportions of minerals, parcels of which he sold to 

 the farmers as patent manures. He maintained that, were he 

 placed in possession of the elements of any given soil, and the 



' I must not be regarded as an opponent of tlic practice of rotting 

 farmj-ard manure under every circumstance. Unrotted manure would if 

 applied, say, to a potato crop, lie in the ground without fertilizing it till 

 alter the tubers had been harvested, nor would it retain moisture like 

 rotted dung. 



