4 On tlie Theory of Manures. 



It has been attempted to simplify the subject, by selecting 

 some one of the constituents of manure as the most essential. 

 Of the four principal and most abundant elements, hydrogen 

 and oxyo-en being got from the water absorbed, and carbon 

 partly from the air and partly from the soil, and not yet pro- 

 perly decided how much from each, nitrogen has been selected. 

 Beino- generally found in combination with carbon and other 

 substances needed as food, being necessary in the transformations 

 carrying on in the circulating sap, assisting greatly in all the 

 fermentations of manures, and being always found in greatest 

 quantity in the spongioles of the roots, and in the young shoots 

 and leaves, wherever vitality is most active, it has, though 

 small in amount as a constituent, been found very important. 

 It has not been found, however, that manures always produce 

 results in proportion to the quantity of nitrogen they contain, 

 nor that croj)s exhaust the fertility of the soil in the ratio of 

 the quantity of nitrogen they take from it. It has been found, 

 also, that great effects have taken place from an augmentation 

 in the usual quantity of the inorganic saline substances of 

 manures ; and hence nitrogen, though perhaps the most essential 

 ingredient taken by itself and with regard to its combinations, 

 yet cannot generally be taken as an exact measure of value for 

 the whole. 



Dr. Madden, in his Essay published in the Highland Society's 

 Transactions ( Quarterly Journal of Agriculture) for June last, 

 takes a more extended view of the subject, and proposes to 

 comj)are the value of manures by — 



1st. The quantity of soluble matter present. 



2d. The facility with which those portions at first insoluble 

 can be rendered capable of solution by the process of decay. 



3d. The quantity of azote (nitrogen) they contain. 



4th. The whole quantity of organic matter possessed by 

 them. 



5th. The quantity of inorganic matter which each contains, 

 possessing the same constituents as the ashes of the crop to 

 which it is applied. 



Bone dust he finds, by analysis, to contain of 



Organic matter, with 

 some saline ma- - 

 terials 



Water - - - _ . . . _ _ 11-5 



soluble in cold water - - - 4-7 



— in hot water - - - 5-5 



— in a weak solution of potass 26'0 



— in a strong ditto - - 15*3 

 L driven ofF afterwards by heat - 6*0 



Phosphate of lime ---..... 28*0 



Carbonate of lime ---_____ 2'8 



100-0 



