NITROGEN 133 



blood, flesh, and bone, and leather tankage which may 

 consist of leather scraps which have not been chemically 

 treated to render them available. Considering the fact 

 that, in the manufacture of leather, the hide is chemically 

 treated to make it resistant to decomposition, it can readily 

 be seen that untreated leather will be one of the last ma- 

 terials to nitrify. Leather tankage is useless without 

 treatment with sulphuric acid, but where so treated its 

 nitrogen is available. Great care should be exercised to 

 ascertain its value to the soil before purchasing any kind 

 of leather tankage. 



(d) Peruvian guano consists of the excrement and car- 

 casses of sea-fowls. It contains high percentages of both 

 phosphoric acid and nitrogen, as well as some potash; 

 but its chief value is due to its nitrogen content. Its source 

 was noted when it was considered as a source of phos- 

 phorus. It needs no treatment before applying. Fresh 

 guano collected from some islands of the Pacific Ocean 

 contains a considerable amount of ammonium carbonate 

 and must be treated with sulphuric acid to fix this ammonia 

 in the form of a sulphate, because the carbonate is very 

 volatile. 



(e) Hoof meal should be classed apart from hides, horns, 

 hair, and feathers. Hoof meal runs to about 14 or 15 

 per cent of nitrogen, and it gives good results in field tests. 

 The chemical methods for determining availability as plant 

 food do not, as a rule, show the real value of this material. 



(/) Hides, horns, hair, and feathers are very resistant 

 to nitrification, and hence they are of low agricultural value 

 unless treatment with sulphuric acid is used to render 

 the nitrogen available. These materials all run high in 

 nitrogen content, but their use, when they cost much, is 

 unadvisable. 



(gr) Wool contains about 17 per cent of nitrogen. In 

 uncleaned wool there is a fatty material known as suint, 

 which contains a large per cent of potash salts, mainly in 



