206 Composition and Value of Guano. 



is burned in the open air it loses from one-half to two- thirds of its 

 weight ; this loss consists of the animal compounds, such as 

 uric acid, «Scc., and the carbonate and other salts of ammonia. 

 Upon an examination of the tables before referred to, it will be 

 found that under this head — 



The lowest per centage (Spec. 7) . is . 37" 78 

 The highest . . (Spec. 3) . „ . 58-82 

 The average of 32 specimens being . . 52*61 



Although the extreme differences above given really occur in 

 genuine Peruvian guano, the amount of variation is not by any 

 means common. In the 32 specimens, only three will be found 

 having a higher per centage of combustible matter than 56, and 

 about the same number falling short of 50 per cent. 



At first sight the proportion of organic matter and ammoniacal 

 salts in guano might seem to be a datum of importance, and so it 

 would be if it were a measure of the ammonia which each sample 

 can supply. Such, however, is not the case. Specimens 1 and 7, 

 which contain very different quantities of organic matter, &c., 

 yield very nearly the same amount of ammonia ; and this holds 

 good in many other instances, which will occur to the reader 

 who examines the tables. An analysis of guano therefore, to afford 

 an accurate notion of its value, must state the quantity of ammo- 

 nia — the proportion of " matters containing ammonia" furnishing 

 no definite information on this point. 



Sand, Sfc. — The proportion of sand in guano is of no great im- 

 portance. It serves, however, to indicate its purity or otherwise. 



In some species of guano a large proportion of sand is found. 

 If the deposit is on the mainland, the sand is introduced into it 

 during its formation by the action of winds ; or if on an island of 

 a loose texture, the guano becomes mixed with the surface matter 

 itself. 



The genuine Peruvian guano is brought from one or more 

 islands about 6 miles from the coast of Peru, and is deposited on 

 a solid rock. Neither of the before-mentioned agencies there- 

 fore come into play, and the manure is consequently almost free 

 from sand or other insoluble substances. In the 32 specimens — 



The lowest per centage of sand (Spec. 1) . is . 1-17 

 The highest ,, ,, (Spec. 31j) . „ . 2-95 



The average of all the specimens being . . . .1*54 



In the great majority of cases the proportion of sand is found 

 to be within 1 and l^ per cent. This C(.mparative uniformity of 

 quantity, and indeed the presence of any sand at all, ceases to sur- 

 prise us when it is remembered that the digestion of birds cannot 



