3i0 



On Guano. 



§ 5. On the Cause of the fertilising Action of Gucmo. 



Though so variable in composition, however, the nature of the 

 substances it appears always to contain enables us to explain why 

 it exerts so marked an effect on the growth of plants, as well as 

 to answer one or two other questions — in regard, for example, to 

 the duration of its action in fertilising- the land — and to the 

 cause of its accumulation on the coast of Peru. 



1 . The most important and most active ingredient contained in 

 the decomposed guano imported into this country is the ammonia. 

 This substance, there is reason to believe, acts in a most energetic 

 manner upon vegetation in every climate — it is one of the most 

 useful ingredients in our farm-yard manures, and though writers 

 differ in opinion as to the amount of influence actually and con- 

 stantly exercised by this compound on the general vegetation of the 

 glohe,^ they all agree in attributing to it a very beneficial action 

 on growing plants in general, when applied to them in a suffi- 

 ciently diluted state. In proportion, then, to the quantity of 

 ammonia it contains will the value of the guano be increased, 

 and hence one reason why the more recent varieties should be 

 accounted the best, and should bring the highest price in the 

 market. 



2. Next to the ammonia, or perhaps equal to it in value, 

 though in the specimens I examined very much less in quantity, 

 is the uric acid. This substance, as it decomposes, gives rise 

 among other products to the formation and evolution of ammonia 

 in considerable quantity. Under the most favourable conditions 

 100 of pure uric acid might yield 40 of pure ammonia. In 

 nature, however, these conditions probably never occur, so that, 

 during its decomposition, numerous other products containing 

 nitrogen are formed (prussic acid among the rest), which it is 

 unnecessary here to specify. We know little that is certain in 

 regard to the action of these products on the growth of plants, 

 but the well-known effect of liquid manure, which in a state of 



earthy salts as they existed in the ash that was left when the guano was 

 heated to redness in the air. The chemical reader will understand that very 

 different numbers would have been obtained had the soluble salts been 

 separated from the insoluble before either of them was heated to redness. 

 This arises from the circumstance that, when the crude guano is heated, the 

 phosphate of ammonia and oxalate of lime are simultaneously decomposed, 

 and phosphate of lime is formed, whereas, were the phosphate of ammonia 

 previously removed by washing, the oxalate of ammonia would, by the 

 burning, be converted only into carbonate. With a view to a merely econo- 

 mical object it did not appear to me necessary to enter into a rigorous 

 examination of the relative proportions of the several salts of ammonia 

 present in such variable quantities in the guano. 



* The prevailing views on this subject, and the reasons on which they are 

 founded, are explained in my ' Lectures on Agricultural Chemistry and 

 Geology,' part i. p. 248. 



