16 Fish Manures. 



With regard to the nitrogen in manures, it may exist in the 

 form of ammoniacal salts, or combined in organic matters which 

 evolve ammonia by their slow decay. The ammonia which the 

 latter are capable of thus yielding, is designated as potential or 

 possible ammonia, as distinguished from the ammonia of the 

 ammoniacal salts, which is generally soluble in water, and is at once 

 disengaged when these matters are mingled with potash or quick- 

 lime. Such is the sulphate of ammonia, which is prepared on a 

 large scale from the alkaline liquid condensed in the manufacture 

 of coal-gas. In Peruvian guano a large amount of the nitrogen 

 is present as a salt of ammonia, and the remainder chiefly as uric 

 acid, a substance which readily decomposes, and produces a great 

 deal of ammonia. In fact, this decomposition takes place spon- 

 taneously, with so much rapidity, that the best guanos may, it is 

 said, lose more than one-fifth of their nitrogen in the form of am- 

 monia in a few months' time, if exposed to a moist atmosphere. 



Other manures, however, contain nitrogen in combinations which 

 undergo decomposition less readily than uric acid. Thus unburned 

 bones yield from six to seven per cent, of ammonia, and dried blood, 

 fifteen or sixteen per cent, while woollen rags and leather yield 

 about as large a quantity. In estimating the value of such mat- 

 ters as manures, the difference in the facility with which they en- 

 ter into decomposition, must be taken into account. Thus if too 

 large quantities of guano are applied to the soil, a portion of the 

 ammonia may be volatilized and lost, while with leather and wool 

 the decay is so slow, that these materials have but little immediate 

 effect as manures. The nitrogen of blood and flesh is converted 

 into ammonia with so much ease, that it may be considered al- 

 most as available for the purpose of a manure as that which is 

 contained in ammoniacal salts. 



Attempts have been made to fix the money value of the am- 

 monia and the phosphates in manures, and thus to enable us from 

 the results of analysis, to estimate the value of any fertilizer con- 

 taining these elements. This was I believe first suggested a few 

 years since, by an eminent agricultural chemist of Saxony, Dr. 

 Stockhardt, and has been adopted by the scientific agriculturists 

 of Great Britain, France and the United States. These values 

 vary of course very much for different countries ; but I shall avail 

 myself of the calculations made by Prof. S. AV. Johnson of New 

 Haven, Connecticut, which are based on the prices of manures in 



e United States in 1857. In order to fix the value of phosphoric 



