COMPOSITION OF GUANO. 457 



This surface soil I have found to be especially rich in phosphate of lime, 

 vvliich has gradually accumulated and remained in it while the volatile 

 and soluble parts of the droppings of the birds have slowly disappeared. 



5°. Guano is the name given to the accumulated dung chiefly of 

 sea birds, which is found upon the rocky promontories, and on the isl- 

 ands that skirt the coast of South America, from the 13th to the 21st 

 degree of south latitude. In that part of America, the climate being 

 very dry, the droppings of the birds have decomposed with exceeding 

 slowness, and upon some spots have continued to accumulate for many 

 centuries, forming layers, more or less extensive, of 10, 20, and at cer- 

 tain places it is said even 60 (?) feet in thickness. In some places 

 the more ancient of these deposites are covered bv layers of drift 

 sand, which tend further to preserve them from decay. In our moist 

 climate the dung of the sea fowl is readily washed away by the rains, 

 so that even where sea birds most abound no considerable quantity 

 of guaiio can ever be expected to collect. 



The solid part of the droppings of birds in general, when recent, con- 

 sists chiefly of uric acid, with a little urate of ammonia, and a variable 

 per-centage of phosphate of lime and other saline compounds. The 

 liquid part, like the urine of other animal^ contains much urea, with 

 some phosphates, sulphates, and chlorides. The uric acid and urea, 

 however, gradually undergo decomposition, and are changed into car- 

 bonate and other salts of ammonia. If applied to the land when this 

 stage of decomposition is attained, they form an active, powerful, and 

 immediately operating manure ; but if allowed to remain'exposed to 

 the air for a lengthened period of time, the salts of ammonia gradually 

 volatilize, and the efficacy of what remains becomes greatly dimin- 

 ished. Hence, the guano which is imported into this country is very 

 variable in quality, some samples being capable of yielding only 7 

 per cent, of ammonia, while others are said to give as much as 25 

 per cent. Of two portions taken by myself from the same box, the 

 one contained 8 per cent, and the other only 1^ per cent, of sand, 

 while their other constituents were as follows : — 



1 • percent- '^ • ^ percent 



Water, salts of ammonia, [Ammonia ' 7-0 



and organic matter ex- | Uric acid '. . 0-8 



pelled by a red heat 23-5 



Sulphate of soda 1-8 



Common salt, with a little 



phosphate of soda 30-3 



Phosphate of lime, with a lit- 

 tle phosphate of magnesia 

 and carbonate of lime 44-4 



100 



Water and carbonic and ox- 

 ahc acids, &c., expelled 

 by a red heat 51-5 



Common salt, with a little 

 sulphate and phosphate 

 of soda ... 11-4 



Phosphate of lime, &c 29-3 



100 



On the other hand, Dr. Ure gives the following as the average re- 

 sult of his analyses of genuine guano : — 



perc««t. 

 Organic matter containing nitrogen, including urate of ammo- 

 nia, and capable of aflfording from 8 to 17 per cent, of am- 

 monia by slow decomposition in the soil 50 



Water 11 



