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return. If it is applied to crops that take a whole year 

 growing, and crops, such as root-crops, and sugar-producing 

 crops, that are specially benefited by the application of 

 phosphatic manures, good result, no doubt, will immediately 

 follow, i.e. it will be palpable in the very first crop grown 

 with this manure. It is best, however, to apply a fairly 

 heavy dose of powdered apatite (say 10 maunds per acre) 

 every 5 years, and grow a crop of sugar-cane the year 

 it is first applied, to make the best immediate use of the 

 fertiliser. 



883. The detection of phosphoric acid in rocks and 

 minerals, is of the greatest value to agriculturists. It can be 

 done by finely pulverising a tolerably large sample of the 

 substance, digesting it in Hydrochloric acid, filtering off the 

 solution and treating it with Ammonium Molybdate. If 

 phosphoric acid be present, a yellow precipitate will follow, 

 and the precipitation which usually takes place very slowly, 

 may be accelerated by frequent stirring with a glass rod. 



884. When a substance contains more than 3 per cent, 

 of phosphoric acid, its presence may be detected in a dark 

 room by the flame test. A little of the mineral, or sub- 

 stance to be tested, is powdered and made into a stiff 

 paste with water. Then a heated loop of 'platinum wire is to 

 be dipped into this paste and returned to the flame of the 

 spiritlamp (or blow-pipe). If phosphates are present, a 

 characteristic dull green flame will be given out, which in a 

 dark room cannot be mistaken. 



885. Apatite, though a very insoluble mineral, is readily 

 dissolved in hydrochloric acid. For the flame test also a 

 little hydrochloric acid may be used z. e. the red-hot platinum 

 loop with the substance tested may be dipped in a bottle of 

 hydrochloric acid and held over the spirit lamp again. Chlo- 

 rides usually give the best colorations. Hence the importance 

 of using hydrochloric acid in testing minerals for phosphates. 



886. Bones. Pbosphatic manures are of very great inv 



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