Composition and Value of Guano. 207 



be carried on without the introduction with their food of a certain 

 portion of some granular substance. 



From the fact that amongst the pure specimens of guano now 

 described, one or two may be selected which contain nearly 3 per 

 cent, of sand, great caution is necessary before a specimen is de- 

 clared to be impure or adulterated, because it contains a larger 

 quantity of insoluble matter than usual ; but there can be no diffi- 

 culty in coming to this conclusion if a high per centage of sand 

 is accompanied with other unusual characters. 



Earthy Phosphates. — It has been before pointed out, that the 

 precipitate which receives this name consists almost entirely of 

 phosphate of lime. Unlike the ingredient which we have just 

 discussed, the proportion of phosphate of lime in guano is of 

 positive importance. 



The lowest proportion (Spec. 1) . is . 19*46 per cent. 

 The highest „ (.Spec. 7) . „ . 34-45 



The average of 32 specimens being , . 24*12 „ 



Here again the exceptional cases are comparatively rare — the 

 majority of specimens affording a proportion of phosphate of lime 

 confined within 20 and 25 per cent. 



Alkaline Salts. — It has been explained that under this head 

 are included the sulphates and muriates of potash and soda, to- 

 gether with any loss occurring in the analysis. Of these ingre- 

 dients the potash is the only one of any importance, as will be 

 more clearly shown presently. The quantity has been ascertained 

 in 16 specimens of guano, and in these it averages 364 per cent. 

 It is not, however, to be thought that it always reaches this high 

 proportion — for in some samples the total amount of alkaline 

 salts is so small, as to preclude the presence of any considerable 

 amount of the alkali. In the 16 cases before alluded to, the 

 alkaline salts average 8T3 per cent., of which 3 64 per cent, is 

 potash. We shall not therefore perhaps be far wrong in esti- 

 mating the potash at something less than one-half of the average 

 proportion of these salts. 



In the 32 specimens the alkaline salts are as follows : — 



The lowest proportion (Spec. 6) . is . 0-61 per cent. 

 The highest „ (Spec. 7) . ,, • 13*48 ,, 



The average of the 32 specimens being . 8*78 ., 



The last number very nearly agrees with that deduced from 

 specimens in which the potash was actually determined, and we 

 shall therefore conclude that the average proportion of this alkali 

 is about 3i per cent. 



The Ammonia.— Oi all the ingredients of Peruvian guano the 

 ammonia is the one of greatest value, and a knowledge of its 



