288 AMMONIA AND NITRIC ACID. 



tivity weve wanting. Lawes and Gilbert supplied these 

 conditions to their field, and hence ensured activity to 

 the ammoniacal salts they used. 



The results obtained by Kuhlmann respecting the 

 effect of salts of ammonia upon meadows are precisely 

 similar. He manured a piece of meadow land with 

 sulphate of ammonia, and obtained a crop of hay larger 

 than the yield of the unmanured plot, because a certain 

 quantity of phosphoric acid, potash, &c. was rendered 

 active, which without the cooperation of salts of am- 

 monia, would not have been the case. On adding 

 phosphate of lime to the salts of ammonia, the activity 

 of the latter was enhanced in an extraordinary degree ; 

 he obtained, 



Return of hay, per hectare, 1844. 



Excess above the 

 unmanured plot, 

 kilo. kilo. kilo. 



(1) By manuring with 250 sulphate of ammonia . . 5564 1744 



(2) " 333 sal ammoniac, with phos- 



phate of lime 9906 6086 



(3) Unmanured plot 3820 



Thus, by sulphate of ammonia alone, Kuhlmann ob- 

 tained rather more than half as much hay again as the 

 yield of the unmanured plot ; and by adding phosphate 

 of lime he gained almost three times as much. 



Those who maintained the theory of the special im- 

 portance to agriculture of nitrogen in manure, formed 

 a similar notion about the cause of fertility in land. 



If, in fact, the efficacy of any manure depended on 

 the enrichment of the soil with nitrogen, exhaustion 

 could be explained only by the diminution of the store 

 of nitrogen ; and the manure would restore fertility 

 when the nitrogen which had been removed in the har- 

 vest was again supplied by it to the field. Accordingly, 

 the unequal fertility of land must be due to the unequal 

 amounts of nitrogen contained in it ; and it would fol- 

 low that the soil richer in nitrogen must be more fruit- 

 ful than one which contained less of this element. 



This theory, too, came to a pitiful end ; since that 



