36 PRACTICAL AGRICULTURAL CHEMISTRY [91-94 



the end of the tube. The paper will become brown. This 

 experiment teaches that when these two substances are 

 mixed ammonia passes off into the air and is lost ; and 

 since ammonia contains nitrogen this loss is a serious one. 



TESTING MANURES 



91. To find the exact value of a manure it is necessary, 

 to make a full quantitative analysis. There are, however, 

 a few simple tests by which the purity of a manure or the 

 composition of a mixed manure may be recognised. These 

 are detailed in paragraphs 92-106. 



92. Ammonia in Guano.— No single test can be 

 applied which will guarantee the purity of a Peruvian guano, 

 but the one described in this paragraph, together with those 

 in the next two experiments, will give a fair idea of its 

 genuineness. Take a little guano in a test-tube, and treat it 

 with potash exactly as was described in the case of nitrogen- 

 ous manures (86). A genuine guano contains ammoniacal 

 nitrogen, and hence ammonia will be evolved, which will 

 turn turmeric-paper brown. 



93. The Ash of Guano.— Place a little guano on 

 a piece of platinum foil, and hold it by means of a pair of 

 crucible tongs in the flame of a Bunsen burner. The 

 guano will first darken in colour, then catch fire and flare 

 up. When it ceases burning a black mass of charcoal will 

 be left. Continue heating until all the charcoal is burned 

 off. The mass now left on the foil is known as the ash of 

 the guano, and should be quite white. If it is brown the 

 guano has been adulterated. 



94. Soluble Phosphoric Acid in Guano. — Treat 

 a small quantity of guano with water in a test-tube as 

 described in paragraph 78. Filter and heat the liquid with 

 excess of ammonium molybdate solution. A yellow pre- 

 cipitate will be formed, showing that the guano contained 



