72 PRACTICAL AGRICULTURAL CHEMISTRY L'246-251 



246. Nitrite. — Boil with water, filter, and test with Kl 

 solution, starch, and HA (197) ; a blue coloration will 

 appear. 



247. Nitrate. — Boil the original substance with water ; 

 filter, cool under the tap, and add very cautiously an equal 

 bulk of strong sulphuric acid ; cool in water. When quite 

 cold add slowly down the sides of the tube a little of a cold 

 solution of FeS0 4 . Where the liquids come in contact a 

 brown ring will be formed. 



248. Phosphate. — A phosphate, if present, will 

 usually have been detected in Table II. (236). It is readily 

 detected by boiling the original substance with dilute 

 HNO3 and then adding a few drops of this solution to 

 ammonium molybdate solution ; a yellow precipitate forms 

 on warming. 



249. Silicate. — A silicate will usually be found in 

 Table II. (236). It may be readily detected if a little of the 

 finely powdered substance is fused with Na 2 C0 3 on plati- 

 num foil, and then treated with HC1. On evaporating to 

 dryness the Si0 2 will be rendered insoluble, so that on 

 treating with HC1 and water the Si0 2 will be left as a white 

 powder (208). 



ANALYSIS OF SUBSTANCES INSOLUBLE IN 

 WATER AND ACIDS 



250. The insoluble substances usually associated with 

 agricultural products are silica, silicates, and phosphates. 



251. Mix the finely powdered substance with six times 

 its weight of fusion mixture (268). Place in a porcelain 

 or, preferably, a platinum crucible. Heat gently at first, 

 then strongly over the blowpipe. Continue the heating until 

 all effervescence ceases. Allow to cool and place the 

 crucible and contents in a beaker, and gently heat with 

 dilute HC1 until the residue is all dissolved, or only gelati- 



