GELATINE, OIL-CAKES, AND UREA. 217 



a On corn-crops of different kinds, under different circum- 

 stances, and applied in different quantities. 



b On root-crops, and especially on the potato, for which salts 

 containing magnesia are alleged by some to be specially 

 adapted. 



c In comparison with equivalent quantities of carbonate of 

 ammonia, carbonate or sulphate of magnesia, and phosphate of 

 ammonia. These comparative trials will throw some light on 

 the part which is performed by each of the constituents in 

 bringing about the result which the compound salt is observed 

 to produce. 



7. Suggestions for experiments with gelatine, oil-cakes, urea, 

 nitrate of urea, and uric acid. 



In connexion with the salts of ammonia and the nitrates, I 

 would suggest experiments with certain other substances con- 

 taining nitrogen, the special and comparative action of which 

 upon growing plants it is desirable to ascertain. I would espe- 

 cially recommend gelatine, the organic or soluble part of bones, 

 rape and other cakes, left by the oily seeds when crushed in 

 the oil-mills, urea, a peculiar substance existing in urine to 

 the amount of about 3 per cent, uric acid, a substance also 

 existing in urine, but in much smaller proportion, and the 

 nitrate of urea, a crystalline compound which is obtained by 

 evaporating urine to a very small bulk, and adding nitric acid 

 to the concentrated liquor. 



These substances contain nitrogen in the following propor- 

 tions : 



Gelatine contains 

 Urea, . 

 Uric acid, 

 Nitrate of urea, 

 Oil-cakes, 



17 per cent of nitrogen. 

 46.7 ... 



36.9 



4 to 



The purposes for which experiments with these substances 

 may be made, are 



1. To ascertain the special action of each upon any given 

 crop, when applied in different quantities, and under different 

 circumstances. 



