200 *THE CANADIAN NATURALIST. [June, 



vening molecules, collapse into dust. In this form they do not 

 occupy a hundredtii part of the volume through which they were 

 previously spread ; and they are, moreover, very apt to be further 

 eompacted by actual fusion during thn agitation. Farm-dung 

 ash is particularly liable to vitrification, because its straw contains 

 both the alkaline and silicious elements of glass. The vitreous 

 or semi-vitreous ash thus produced by incineration is but slightly 

 soluble. In a word, the effect of incineration on farm-dung 

 closely resembles that produced by Liebig's furnace-treatment on 

 his Mineral Manure. 



These considerations should be attentively borne in mind, in 

 estimating the value of experiments adduced to prove the ineffi- 

 cacy of the cinereal constituents of farm-dung, as contradistin- 

 guished from its ammoniacal ingredients.* 



The Nitrogen THEoaY, and the Doctrine of Specific 

 Manures. — It is not however to be inferred from the foregoing 

 remarks that cinereal plant-food, such as Liebig's manure (or as 

 the ash of incinerated dung), even if supplied in a p^ rfectly solu- 

 ble form, would be indiscriminately applicable to increase in an 

 dqual degree the immediate productive power of all conditions of 

 soil, for every kind of crop. It was against this undue pretension, 

 which was supposed to follow from some of the statements put 

 forth in Liebig's earlier works, that the advocates of the so-called 

 " Nitrogen theory" (who also support the doctrine of '* Specific 

 manures") originally raised their flag. It may be doubted whether 

 the illustrious author of the mineral theory, even in his earliest 



* In pointing out the valuable distributive properties of farm-dung 

 the reporter would not be supposed to overlook the still wider diffa- 

 sion of fertilizing matters obtainable by liquid manuring. This system, 

 indeed, has been already indicated as the principal distributive mech m- 

 ism of the future. It enables the farmer to direct, from a central point 

 radiating streams of plant-food to his remotest fields ; and by the mere 

 turning of a tap, to adopt the ' supply with the utmost nicety to the 

 requirements of every plot. The cartage-cost, and manual labor incur- 

 red in spreading dung upon the soil, may thus to a great extent be 

 replaced by steam-power; or even, in favorable cases, by the still 

 cheaper force of gravitation. To soils requiring a carbonaceous supply 

 3uch as the cattle-litter in dung affords, this material (cut up) might 

 perhaps be economically conveyed in suspension in the liquid manure- 

 streams. For clay, and other insoluble matters capable of suspension 

 in water, this mode of distribution has been found available. 



