218 UREA AND URIC ACID, HOW THEY ACT. 



2. To determine whether their respective sensible effects are in 

 proportion to the quantity of each applied, when different doses 

 are used ; and whether they are directly as, or have any relation 

 to, the proportions of nitrogen they respectively contain. 



3. Whether their action is in any way different from that of 

 the salts of ammonia or the nitrates when applied in quantities 

 containing the same weights of nitrogen, and whether the dif- 

 ference, if any, is the same in the case of all crops. 



4. In comparing these substances with the salts of ammonia, it 

 should be recollected that urea readily decomposes and becomes 

 converted into carbonate of ammonia. This decomposition is 

 very likely to happen when urea is mixed with the soil, and 

 therefore its action may be very analogous to that of carbonate 

 of ammonia. The purpose, therefore, of comparative experi- 

 ments between urea and this carbonate is to ascertain how far 

 the peculiar form of combination of nitrogen in each affects its 

 action upon the plant. 



5. Again, one-third of the nitrogen in the nitrate of urea exists 

 in this compound in the state of nitric acid. This nitrate, there- 

 fore, may exercise an action not unlike that of the nitrate of 

 ammonia, with which it would be interesting to compare it. 



We have, in fact, in regard to urea, these several questions 

 to ask 



a Does urea produce an effect similar or equal to that of 

 ammonia, when the quantities of each applied contain equal 

 weights of nitrogen ? 



b Does nitrate of urea act differently in any way from urea, 

 when equal quantities of nitrogen are applied ? What influence 

 upon the result has the circumstance that one half of the nitrogen 

 in the nitrate of urea is in the form of nitric acid, and the other 

 half in the form of urea ? 



c What is the effect of nitrate of ammonia compared with 

 nitrate of urea ? In both, one half of the nitrogen is in the 

 state of nitric acid, the other half in that of urea or of am- 

 monia. 



These questions indicate the purposes for which the experi- 

 ments are to be made, and the search for answers to them must 

 be very interesting. 



