221, 222] Analysis of Guano 137 



an Argand, being careful not to exceed a dull-red heat, or 

 some of the alkaline salt will fuse and render the mass difficult 

 to remove from the dish. 



The ash of a pure guano should be perfectly white. 



Weigh the dish and guano after burning, and enter the loss 

 as organic matter plus moisture. 



Transfer the residue to a beaker, washing the last traces off 

 the dish with a little dilute HC1 j dissolve up in strong HC1, 

 and proceed as in the case of mineral phosphates (see para- 

 graphs 198 and 199), adding, however, only \\ gram of ammo- 

 nium oxalate. 



221. Nitrogen. — The guano should be tested for nitrates 

 thus : About 5 grams of guano are extracted with water ; to 

 the filtered solution are added a small quantity of indigo solu- 

 tion and strong sulphuric acid equal in bulk to the water used. 

 Bleaching of the liquid indicates the presence of nitrates. 



Should nitrates be absent, the acid method may be used 

 (see paragraphs 90-95). 



Should nitrates be present, the modified method described 

 in paragraph 99 must be used. 



The anwionia in a true guano should be about a quarter of 

 the organic matter. 



Ordinary guanoes do not contain nitrates, with the ex- 

 ception of Bats' guano, which probably contains nitric acid 

 in combination with lime. The name 'guano,' however, is 

 so popular with farmers that many compound artificial 

 manures are sold as guano. Hence the necessity for testing 

 with indigo. 



222. Calculation. — On calculating out the quantities ot 

 CaO and P 2 5 a true guano will show an excess of P 2 5 over 

 the CaO. Should the CaO be in excess, the result is entered 

 exactly like that of bones. Should the P 2 5 be in excess, there 

 are two methods in use. The most scientific is to put down in 



