The tests for a salt, potassium nitrate, for example, are the tests not for KNO 3, but for its ions K and NO 3, and in cases of double decomposition it is always these ions that are exchanged for those of other substances.
Dilute mineral acids decompose it with the formation of insoluble silver cyanide and hydrocyanic acid: KNC AgNC+HN03=HCN+ KNO 3 +AgNC. A boiling solution of potassium chloride with the double cyanide gives silver chloride and potassium cyanide.
The potassium salt may be prepared by adding potassium cyanide to ferrous sulphate solution, the brown precipitate so formed being then heated with potassium nitrite: 5 KNC + 2 FeSO 4 = 2 K 2 SO 4 + KFe2(NC)5, 2 KFe 2 (NC) 5 + 2 KNO 2 = 2 FeO + 2 K2Fe(NC)5 NO.
The amount of hydrocyanic acid in a solution may be determined by adding excess of caustic potash and a small quantity of an alkaline chloride, and running into the dilute solution standard silver nitrate until a faint permanent turbidity (of silver chloride) is produced, that is, until the reaction, 2KNC+AgNO 3 = KAg(NC) 2 - -KNO 3, is completed.
The first aliphatic diazo compound to be isolated was diazoacetic ester, CH N2 CO 2 C 2 H 5 i which is prepared by the action of potassium nitrite on the ethyl ester of glycocoll hydrochloride,HCl NH2 CH2 C02C2H 5 -1-KNO 2 =CHN 2 CO 2 C 2 H 5+ KCI+2H 2 O.