358 CONSIDERATION OF CARBON COMPOUNDS. 



atives of aromatic compounds, for which reason the consideration of 

 the whole group will be deferred until benzene and its derivatives 

 are spoken of. The large number of basic substances found in putre- 

 fying matter and termed ptomaines will also be considered later on. 



Cyanogen compounds. Cyanogen itself does not occur in nature, 

 but compounds of it are found in a few plants (amygdalin), and also 

 in some animal fluids (saliva contains sodium sulphocyanate). Gases 

 issuing from volcanoes (or from iron furnaces) sometimes contain 

 cyanogen compounds. 



The univalent residue cyanogen, C=N, or CN, was the first 

 compound radical distinctly proved to exist, and isolated by Gay- 

 Lussac in 1814. The name cyanogen signifies " generating blue/' in 

 allusion to the various blue colors (Prussian and TurnbulPs blue) 

 containing it. (The symbol Cy, sometimes used in place of CN, has 

 been adopted merely to simplify the writing of formulas of cyanogen 

 compounds). 



Cyanogen and its compounds show much resemblance to the halo- 

 gens and their compounds, as indicated by the composition of the 

 following substances : 



C1C1, HC1, KI, HC1O, 



Chlorine, Hydrochloric Potassium Hypochlorous 



acid. iodide. acid. 



CNCN, HBr, KCN, HCNO, 



Cyanogen. Hydrobromic Potassium Cyanic acid. 



acid. cyanide. 



CNC1, HCN, AgCN, HCNS, 



Cyanogen Hydrocyanic Silver Sulphocyanic 



chloride. acid. cyanide. acid. 



Dicyanogen, (CN) 2 . The unsaturated radical CN does not exist 

 as such in a free state, but combines whenever liberated with another 

 CN, forming dicyanogen. It may be obtained by heating mercuric 



cyanide : 



Hg(CN) 2 = Hg + 2CN. 



It is a colorless gas, having an odor of bitter almonds, and burn- 

 ing with a purple flame, forming carbon dioxide and nitrogen ; it is 

 soluble in water, and may be converted into a colorless liquid by 

 pressure ; it acts as a poison, both to animal and vegetable life, even 

 when present in but small proportions in the air. 



Hydrocyanic acid, HCN = 27 (Cyanhydric acid, Hydrogen 

 cyanide, Prussic acid). This compound is found in the water distilled 

 from the disintegrated seeds or leaves of amygdalus, primus, laurus, 



