WITH THE NITRATES. 183 



2. Experiments with equivalent quantities of the three nitrates 

 tried against one another in the same circumstances and upon 

 the same crop. Does the nitrate of soda really promote the 

 growth of barley more than the nitrates of potash or lime do ? 



3. With each of the nitrates tried in different doses applied 

 all at once for example, in doses of , 1, 1J, 2, 2, and 3 cwt. 

 per acre. These will throw light upon the interesting question 

 suggested by the experiments detailed in the preceding section. 



4. With the same quantity applied at different periods in 

 March, April, May, &c., and with the same quantity divided into 

 two or three portions, and applied at as many successive periods. 



5. Do they really, and in all cases, affect that is, injure the 

 quality of corn, especially of wheat? and what is the nature 

 of the difference they are said to cause ? This may require a 

 chemical, as well as a practical and mechanical examination of 

 the grain. 



6. The effects of these nitrates on soils of different degrees 

 of richness. Do they pay best when applied to such as are poor 

 in available (not inert) vegetable matter ? 



7. Their effects compared with equivalent quantities of the 

 carbonates of potash and soda, or of the chlorides of potassium, 

 sodium, and calcium. By these substances the alkaline matter, 

 without the nitric acid, of the nitrates, would be brought within 

 the reach of the plant, and the true value of the nitric acid 

 would be illustrated. 



8. Their effects, compared with those of other substances con- 

 taining much nitrogen, such as urea, gelatine, salts of ammonia, 

 &c., and which have nearly as great a degree of solubility. To 

 this class of experiments I shall revert in a succeeding chapter.* 



9. As I have already thrown out the conjecture that some 

 of the special effects of the nitrates in the soil or in the plant 

 may be due to the large proportion of oxygen they contain, and 

 the ease with which they give up this oxygen, comparative 

 trials with other substances containing much oxygen would not 

 be void of interest. Among such substances, the chlorate of 

 potash is one of the best. This salt is expensive, and we could 

 scarcely hope ever to use it for agricultural purposes ; but with 



* See Chapter xiii. 



