MANURES 55 



carried to the earth in the form of the ammonia and nitric 

 acid of the atmosphere. As nitrogenous matters exist but Nitrogenous 

 sparingly in most soils, they are easily exhausted when crops ^n"soon " 

 are continually reaped off the land ; and hence the exhausted, 

 necessity for restoring them in the form of special manure, 

 if the soil is to be kept fertile. The most important and the 

 best known of the nitrogenous manures is Guano^ which, as 

 a fertiliser of the soil, ranks next to farm yard manure. It 

 is the dry dung of sea-birds, found principally on the coast Composition 

 and the adjacent islands of Peru, and it contains from 8 to °^ s^^no- 

 20 per cent, of ammonia. As rain rarely or never falls in 

 these places, the dung has retained its soluble nitrogenous 

 constituents and these give value to the manure. Some of 

 the best guano deposits have become exhausted, and so 

 the manure now supplied under that name is very often of 

 an inferior quality, hence the necessity of particular care in 

 purchasing the article ; some buyers, indeed, exercise so much 

 caution in the matter as to require a chemical analysis of the 

 manure they are about to purchase. Guanos contain phos- 

 phates of lime and magnesia, and sometimes these substances 

 are in such large proportions as to render the manure partly 

 a phosphatic one. Rain and sea-water dissolve out the 

 nitrogenous substance, and when guano is taken from 

 places subject to these influences it is found that the nitro- 

 genous matters are low in quantity and that the phosphates Two kinds 

 are abundant. Consequently there are two kinds of guano °^ guano. 

 one remarkable for its nitrogenous substances which is called 

 nitrogenous guano, and the other called phosphatic guano 

 on account of the abundance of phosphates in it. 



The principal other nitrogenous manures are sulphate of 

 ammonia^ and nitrate of soda. They are richer in ammonia 

 than even guano ; and, as they are very soluble, they are 

 used to stimulate, or to whip, as it were, the soil into doing Soil stimu- 

 more work ; they are on this account sometimes called '^"'^• 

 ^'stimulants" or ''whips." Their effect is immediate and 

 marked. In a few days after application of the manure, 



