AND THE PARACYANIC ACID. 37 



4. Heated with potassium in close vessels, a violent combustion takes place, 

 and a compound is formed, which, when dissolved in water, gives with nitrate of 

 sUver a white precipitate. Dried and heated to redness, this precipitate gives off 

 cyanogen and leaves metallic silver. The compound formed therefore is cyanide 



of potassium. 



5. Prepared by heating bicyanide of mercury, it is exceedingly httle soluble 

 in a solution of caustic alkali, and is very slowly decomposed when boiled with 

 it. During the boiling ammonia is evolved, and oxalic acid should remain in the 

 solution for NC, + 3H0 = NHa + C. O3. Prepared by heating to redness the 

 deposit from cyanogen in alcohol, it is slightly soluble in a boiling solution of 

 caustic potash, givmg it a dark brown colour. Acids precipitate it apparently un- 

 changed. 



6. Fused with dry hydrate of potash, ammonia is evolved. Intunately mixed 

 with caustic or carbonate of potash, and heated to incipient redness in the open 

 air for some time, a salt is formed, possessing the properties of cyanate of potash. 

 With nitrate of silver it gives a white flocky precipitate. With nitric acid, violent 

 effervescence from the evolution of carbonic acid, while the iiltered solution, eva- 

 porated to dryness, gives a mixture of nitrates of potash and ammonia. 



7. Concentrated muriatic acid acts upon it very shghtly, becoming pale yel- 

 low. 



III.— Action of Sulphuric Acid on Paracyanogen. 



Concentrated sulphuric acid (SO3 4- HO), dropped upon paracyanogen in the 

 state of fine powder and gently heated, is absorbed by it, forming a dry mass. A 

 larger quantity of acid, aided by heat, dissolves the paracyanogen without any 

 sensible evolution of gas. The solution is of a deep bro>raish red colour, more or 

 less thick. Water decomposes it, throwing Aowa. the paracyanogen apparently 

 unchanged. It is difllcult, by washing, to free the precipitate entu-ely from sul- 

 phuric acid. A portion of it boUed in water, dried and burned with oxide of cop- 

 per, gave a gas of which 61.6 vols, left 20, and 82.5 left 26.5, so that the ratio of 

 the carbon to the nitrogen is not sensibly altered. 



If the temperature be raised too high during solution, or if the solution be 

 heated to 400' or 500° F., the sulphuric acid and paracyanogen are mutuaUy de- 

 composed, sulphurous and carbonic acids are given off, and sulphate of ammonia 

 is sublimed. The gases are evolved in the proportion nearly of one volume sul- 

 phurous to two of carbonic acid. This agrees with the formula, 



NCa + 2S0 -I- 3H0 = NH3 + SO3 + 2C0, + SO2. 

 During this decomposition, a portion of the paracyanogen becomes oxidised, para^ 

 cyanic acid being formed, hence the volume of sulphurous acid obtained is gene- 



