364 CONSIDERATION OF CARBON COMPOUNDS. 



While apparently this decomposition consists merely in a removal 

 of two atoms of potassium from two molecules of potassium ferro- 

 cyanide, the change is actually more complete, as the atoms arrange 

 themselves differently, the iron passing also from the ferrous to the 

 ferric state. 



Potassium ferricyanide crystallizes in red prisms, soluble in water. 

 It forms, with ferrous solutions, a blue precipitate of ferrous ferricy- 

 anide, or TurnbuWs blue : 



K 6 Fe 2 (CN) 12 + 3FeS0 4 = = 3K 2 SO 4 + Fe 3 Fe 2 (CN) 12 . 



With ferric solutions no precipitate is produced by potassium ferri- 

 cyanide, but the color is changed to a deep brown. 



Nitro-cyan-methane, CH 2 .CN.N0 2 (Fulminic acid}. This substance may be 

 looked upon as a derivative of methane, CH 4 , in which two atoms of hydro- 

 gen are replaced by cyanogen and NO 2 respectively. It is not known in the 

 separate state, but its combinations with metals are well known, especially 

 mercuric fulminate, which is manufactured and used as an explosive in percus- 

 sion caps, etc. It is made by adding alcohol to a solution of mercury in nitric 

 acid. Silver fulminate can be obtained by a similar process. 



48. BENZENE SERIES. AROMATIC COMPOUNDS. 



General remarks. It has been stated before that all organic com- 

 pounds may be looked upon as derivatives of either methane, CH 4 , 

 or benzene, C 6 H 6 , these derivatives being often spoken of as fatty and 

 aromatic compounds respectively. The term aromatic compounds 

 was given to these substances on account of the peculiar and fragrant 

 odor possessed by many, though not by all of them. Benzene and 



QUESTIONS. 461. What are the three chief forms in which nitrogen enters 

 into organic compounds ? 462. What are amines and amides ; in what re- 

 spects do they resemble ammonia compounds ? 463. What is cyanogen, what 

 is dicyanogen, and how is the latter obtained? 464. How does cyanogen 

 occur in nature, and which non-metallic elements does it resemble in the con- 

 stitution of various compounds? 465. Mention some reactions by which 

 hydrocyanic acid is formed, and state the two processes by which the official 

 diluted acid is obtained. What strength and what properties has this acid ? 

 466. State the composition of pure potassium cyanide and of the commercial 

 article. How is the latter made? 467. Give reactions for hydrocyanic acid 

 and cyanides. 468. Explain the constitution and give the composition of 

 ferro- and ferricyanides. 469. Give composition, mode of manufacture, and 

 tests of potassium ferrocyanide. 470. What is red prussiate of potash, how 

 is it obtained, and by what reactions can it be distinguished from the yellow 

 prussiate ? 



