Composition and Value of Guano. 



201 



eventually be derived from the guano. Dr. Ure (who has pub- 

 lished an able paper on the analysis of guano in this Journal, 

 vol. v. p. 287) has called the former the actual and the latter the 

 potential ammonia ; and in making this distinction he obviously 

 considers it important for the farmer to know how much is and 

 how much will be available to the crop for which the guano is 

 applied. If we had any knowledge of the time which these ani- 

 mal compounds require for their decomposition when distributed 

 through any given soil, some advantage might accrue from this 

 refinement, although from the ever-changing circumstances to 

 which a manure is exposed in the soil, the distinction would 

 possess little practical utility ; but it appears to me that in the 

 absence of such knowledge it is far wiser to take the more simple 

 view. It is believed therefore that the value of the organic part 

 of guano is solely dependent upon the proportion of ammonia 

 which it can eventually supply, without reference to the present 

 state of the compounds which will furnish it. 



With respect to the particular constituents which constitute 

 the mineral value of guano there can be little doubt : magnesia 

 and oxide of iron, as existing in minute quantity only, are already 

 disposed of; soda, whether in the state of common salt or in any 

 other form, exists in such small proportion, and, as will be pre- 

 sently shown, could be supplied from independent sources at such 

 a trifling cost, that little or no money value can be attached to it : 

 the same is true of the sulphuric acid, for which gypsum at an 

 almost nameless expense would be an ample substitute. There 

 only now remains the phosphoric acid combined with lime and 

 the potash ; and these with the ammonia are really the important, 

 and the only important, ingredients in guano. 



If the arguments which have been brought forward are consi- 

 dered satisfactory, we shall have arrived at a much simpler notion 

 of the agricultural value of guano than would be derived from an 

 examination of its recondite analysis. The only important consti- 

 tuents will be reduced to these : — 



1. Ammonia or its elements. 



2. Phosphate of lime. 



3. Potash. 



It is proposed in a later part of this paper to consider the 

 money value of guano and its constituents, and it will then be 

 more apparent that the view we have now taken of its compo- 

 sition is a just one. In the meanwhile we may properly intro- 

 duce the analysis of a number of specimens which have been 

 examined upon the principles now brought forward. 



The following table contains the analysis of eight specimens of 



