190 
Peruvian Guano. 
Organic Matter and Salts of Ammonia. — For all practical pur- 
poses it is quite sufficient to determine together organic matters 
and ammoniacal salts, and to indicate how much ammonia will 
be produced by 100 parts of guano on its final decomposition in 
the soil. 
The salts of ammonia, as well as the organic matters, include 
several distinct chemical compounds. Phosphate, sulphate, 
oxalate, urate, and carbonate of ammonia are constantly present 
in Peruvian guano ; but the relative proportion of these salts 
varies to a considerable extent in different samples. The 
organic matter includes uric acid, a little urea, oxalic acid, 
guanine, and other nitrogenised substances, and also butyric, 
phocenic, and similar fatty acids, to which the peculiar and 
characteristic smell of guano is principally due. With the 
exception of the fatty acids, all these organic substances are 
rich in nitrogen, and very prone to suffer decomposition in 
the presence of water. The most important product of their 
decomposition is ammonia. The strong and pungent smell of 
guano damaged by sea-water is due to ammonia, and indicates 
a partial decomposition which the nitrogenous organic matters 
have sustained. Such a decomposition does not take place 
without loss of ammonia. Hence dark-coloured and pungent- 
smelling samples are generally poorer in nitrogen, and less 
valuable than those which are light-coloured, dry, and far less 
pungent. Uric acid and urate of ammonia, which are nearly in- 
soluble in water, contain fully one-third of their weight of 
nitrogen. As long as guano is kept in a dry atmosphere, the 
nitrogen in these compounds remains in a fixed condition. Under 
the influence of oxygen and a certain temperature, uric acid in 
the presence of water passes through a very remarkable series of 
transformations, producing allantoin, urea, and oxalic acid. Urea 
in its turn is readily resolved into carbonate of ammonia. These 
changes in the nitrogenised constituents proceed rapidly when 
guano is incorporated with a moist soil. It cannot, therefore, be 
doubted that the nitrogenous matters of guano, in virtue of the 
ammonia they produce, are as useful to vegetation as the actual 
ammonia which occurs in it in the shape of ammoniacal salts. 
For all practical purposes, therefore, the distinction • between 
actual ammonia and potential ammonia * is of little significance, 
and the same money-value which is given to the actual ammonia 
may with propriety be assigned to the ammonia which guano is 
capable of yielding on decomposition. 
Oxalic acid, it will be noticed, is a product of decomposition 
of uric acid, and therefore is always present in damaged guano 
* That is to say, the ammonia which nitrogenous matters are capable of 
evolving gradually in the soil. 
