95-98] TESTING MANURES 37 



phosphoric acid in a soluble state. The guano may be 

 distinguished from superphosphate by moistening a small 

 quantity on a tile and laying a piece of blue litmus over it. 

 The litmus will not change. If this be tried with super- 

 phosphate the litmus-paper will be reddened. 



95. Volatility of Sulphate of Ammonia. — Place 

 a few crystals of pure sulphate of ammonia on a piece of 

 platinum foil, and heat over a Bunsen flame. The crystals 

 will first of all melt, then white fumes will rise from the 

 substance, and finally it will vanish entirely, leaving no 

 trace whatever on the foil. - Repeat the experiment with a 

 few crystals of commercial sulphate of ammonia. Exactly 

 the same series of changes will take place, except that a 

 slight film of impurity will be left on the foil. The smaller 

 this film, the purer the sulphate will be. 



06. Thiocyanates in Sulphate of Ammonia.— 

 Occasionally sulphate of ammonia contains a powerful plant 

 poison, known as thiocyanate of ammonia, which should 

 always be tested for. Add to a solution of ammonium 

 thiocyanate a few drops of ferric chloride solution ; a blood- 

 red liquid will be formed. Now make a solution of com- 

 mercial sulphate of ammonia in water and treat in the same 

 way by adding a drop of ferric chloride. Should the least 

 red coloration occur, the sulphate is unfit for use. 



97. Action of Heat on Bones.— Samples of bones 

 can usually be recognised by their appearance, except when 

 in the state of bone-flour. Bone-flour may be recognised 

 by the following test. Heat a little of the substance on 

 platinum foil as in paragraph 93. The bones will give off 

 an offensive smell, which is easily recognisable. The sub- 

 stance will next blacken from the formation of carbon, 

 and finally become quite white again, owing to the organic 

 matter being burnt away and only ash left. 



98. Action of Acid on Bones.— Place a small 

 quantity of bone-flour at the bottom of a test-tube and add 



