204 GELATINE COMPARED WITH NITRATE OF SODA. 



with the nitrates which I have analysed in the preceding section 

 appear to justify our conclusion that each compound exercises 

 an action special to itself, and to reject the opinion that the 

 proportion of nitrogen in such fertilising substances determines 

 the amount of their sensible action upon the crop. 



But we have other experiments also, the results of which 

 tend to establish the general principle that the state of chemical 

 combination in which the nitrogen exists, in any substance, 

 influences very much its sensible effect upon a crop. Gelatine 

 and rape-cake contain nitrogen, the former in large proportion, 

 and both promote vegetation in a striking degree. But the 

 fertilising effect of this nitrogen is materially affected by the 

 state of combination in which it exists in them respectively. 

 This is shown by the results of certain experiments upon tur- 

 nips detailed in the preceding chapter, p. 193, and to which I 

 refer the reader. It is very distinctly brought out also by 

 three other series of experiments which I shall here introduce. 



1. With gelatine compared with nitrate of soda and sulphate 

 of ammonia upon grass. Along with the other substances 

 employed in his experiments upon hay, Kuhlmann tried also 

 the gelatine of bones. This was obtained by boiling bones in 

 the process for extracting the fat, before burning them for the 

 manufacture of animal charcoal. It was applied in the liquid 

 form, at the rate of 500 kilogrammes of the dry gelatine to the 

 hectare, or 4 cwt. per acre. The applications were made in 

 1844 and 1846, the plots being undressed in 1845. In the 

 following table the results, per hectare, are thrown into a com- 

 parative form : 



Quantity Nitrogen Nitrogen Increase Increase for 



applied in the per cent in applied per of hay in the 100 kilos, of 

 two years, the manure, hectare. three years. nitrogen. 



Sulphate of ammonia, 500 kilos. 21.2 106 kilos. 3291 kilos. 3105 kilos. 



Nitrate of soda, . 500 ... 16.6 83 ... 3827 ... 4610 ... 



Nitrate of lime, . 500 ... 17.1 86 ... 2204 ... 2562 ... 



Gelatine, . . 1000 ... 17.0 170 ... 4866 ... 2862 ... 



The last column shows an approximation among the compa- 

 rative effects of gelatine, sulphate of ammonia, and nitrate of 

 lime. Whether this indicates a real or only an apparent simi- 

 larity of action in these substances, must be cleared up by future 

 experiments. 



