GUANO 



747 



Dr. Ure drew a distinction between what he called the actual and potential ammonia, 

 i.e. between ammonia and ammoniacal salts ready formed, and compounds, such as 

 uric acid, which during their decay are gradually converted into ammonia. It appears 

 that recent guano contains from 3 to 5 per cent, of uric acid, whilst the older deposits 

 contain generally less than 1 per cent. No doubt the guano at the time of its depo- 

 sition consisted chiefly of uric acid ; and it is this uric acid which has become con- 

 verted into salts of ammonia ; for the excrements of birds which live chiefly on fish 

 are found to contain from 50 to 80 per cent, of uric acid. It is also an established 

 truth in agricultural chemistry that a manure which contains bodies capable of gra- 

 dually yielding up any valuable compound, such as ammonia, are more useful than 

 those which contain that compound ready formed, and in the state of soluble combi- 

 nations, which the first storm of rain may wash away from the roots of the plants, 

 where they are required. Nevertheless, admitting the truth of all this, the writer is 

 of opinion (and he believes this is the general experience of agriculturists) that the 

 importance of this distinction between actual and potential ammonia has been rather 

 exaggerated ; and that generally it is enough for all practical purposes, in estimating 

 the value of a guano, to determine the total quantity of nitrogen present in every form, 

 and to consider it as representing an equivalent quantity of ammonia ' in esse ' or 

 ' in posse.' 



Potash. Of the two alkalis, potash and soda, the soil usually contains more than 

 sufficient soda for the supply of vegetation ; it is therefore chiefly potash which it is 

 necessary to add in the form of manure. 



Besides, even the best guano always contains a considerable quantity of common 

 salt, viz. from 1-0 to 2'5 and even 5 per cent. 



Mr. Way, in his valuable paper, * On the Composition and Value of Guano,' only 

 gives the quantity of alkaline salts, not having determined the potash ; but the average 

 quantity of potash in genuine guano may be seen by referring to the analyses before 

 given in detail, and will be found to vary from 3 to 4 per cent. 



However, in estimating the value of guano the knowledge of the quantity of potash 

 is by no means of the same importance as of the ammonia, or of the phosphoric acid. 



Phosphoric acid. The phosphoric acid is second in importance to no other consti- 

 tuent than the ammonia ; being essential for the development of the seeds and all those 

 parts of the vegetable organism which serve as foods in the production and restoration 

 of the flesh and bones of animals. It exists in the guano (as is shown by the pre- 

 ceding detailed analyses) in combination with ammonia, potash, soda, and lime. 



In most analyses the quantity of phosphate of lime, 3CaO,P0 5 , is given instead of 

 phosphoric acid, PO 3 or 3HO.P0 5 ; but 156 parts of phosphate of lime (3CaO,P0 5 ) 

 correspond to 72 of phosphoric acid (PO 5 ), or as 13 to 6. 



The amount of phosphate of lime in the several varieties of guano is as follows : 



Peruvian. 



From analyses of 9 samples by Way, imported in 1847-8 



From Mr. Way's analyses of 10 samples, imported in 

 1848-9 .... . 



From Mr. Way's analyses of 14 samples, imported in 



1849 



Angamos. 



From 2 analyses by Dr. Ure . :v ,:c vr. '- c.*l* " '"* 

 Ichaboe. 



From 1 1 analyses by Dr. Ure and Mr. Teschemacher 

 Patagonian. 



From analyses of 14 samples by Dr. Ure and Mr. Tesche- 

 macher . . . ; ;; i '. . 

 Saldanha Bay. 



From analyses of 9 samples by Mr. Way 



From analyses of 9 samples by Dr. Ure and Mr. Tesche- 

 macher . . . . . . . . - - <.' 



Kooria Mooria. 



From analyses of 3 samples by Mr. Nesbit 



From analyses of 3 samples by Mr. Apjolm . 



Maxi- 

 mum 



34-45 

 25-30 

 28-98 

 22-00 

 37-00 



65-5 



60-96 



62-5 



25-50 

 28-50 



Mini- 

 mum 



19-46 

 21-31 

 21-28 

 18-50 

 26-00 



29-3 



49-01 



51-0 



2-80 

 5-84 



Mean 



26-95 

 23-30 

 25-13 

 20-25 

 31-50 



47-4 



54-98 



56-7 



14-15 

 17-17 



So that the average quantity of phosphate of lime in the several specimens is as 

 follows : 



