OX.\LATE OF AMMONIA IX GUANO. 259 



efficacious than bone-eartli alone, lias still a difTercnt action 

 from guano. The great distinction between the two lies 

 in the greater rapidity of the action of the guano in the 

 first year, and often even in the course of a few weeks, 

 whilst in the year after it is barely perceptible ; that of 

 the bone-earth, on the other hand, is comparatively slight 

 in the first year, but increases in the following. 



The cause of this difference of action is the oxalic acid 

 in Peruvian guano, which often amounts to from 6 to 10 

 per cent. If guano is subjected to lixiviation, the water 

 chssolves sulphate, phosphate, and oxalate of ammonia, 

 which latter salt crj^stallises out abundantly upon evapo- 

 rating the solution. But if the guano is moistened with 

 Avater, w^ithout hxiviating, and is then left to itself, it is 

 found, upon extracting with water portions of the mix- 

 ture from time to time, that the proportion of the oxahc 

 acid in the solution gradually decreases, whilst that of 

 the phosphoric acid increases. A decomposition takes 

 place in this moistened condition of the guano, through 

 the agency of the sulphate of ammonia, by which the 

 phosphate of lime is converted into oxalate of lime and 

 phosphate of ammonia. Peruvian guano is, in this 

 respect, a very remarkable mixture, which could scarcely 

 have been more ingeniously compounded for the purposes 

 of the nutrition of plants ; for the phosphoric acid in it 

 becomes soluble only in a moist soil, through which it 

 then spreads in form of phosphate of potash, phosphate 

 of soda, and phosphate of ammonia. 



The action of guano may rather be compared to a 

 mixture of superphosphate of lime, ammonia, and salts 

 of potash, which, indeed, in many cases, is equal to it. 

 On a soil abounding in lime, guano is, however, decidedly 

 more advantageous than superphosphate of lime, since 

 the latter, upon coming in contact with the carbonate of 



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