374 ORGANIC CHEMISTRY. 



940. Six parts of nut-galls to four of 



Give the pro- 



cess of its copperas, are found to be the best propor- 



preparation. tiong for prO( } U cing a permanent ink. The 



galls are to be boiled with water, the decoction strained, 

 and mixed with copperas solution. Gum and cloves 

 are added, the former to keep the coloring matter of the 

 ink from settling, and the latter to prevent its moulding. 

 After a ripening of a month or more the liquid is 

 strained. The coloring matter of ink is immediately 

 produced in a solution of copperas, as a bulky precipi- 

 tate, by the addition of tincture of galls, and a little 

 nitric acid. 



HYDROCYANIC ACID. 

 941. CYANOGEN. Before proceeding 



Mention the . . 



composition with the description of hydrocyanic, or 



P mssic acid > the production of cyanogen, 



which enters into its 

 composition, will be briefly consid- 

 ered. Cyanogen is a colorless gas, 

 with a peculiar odor, resembling 

 that of peach pits. It is nearly twice 

 as heavy as atmospheric air. It 

 burns with a beautiful purple flame. 

 Cyanogen is a compound radical, 

 posssessed of important analogies to 

 chlorine, and the other electro-neg- 

 ative elements. Its molecule contains one atom of ni- 

 trogen and two of carbon. 



How is cyano- 942. PRODUCTION. Cyanogen may be 

 gen prepared? expelled from the cyanide of mercury, by 



