332 SMITH'S INTERMEDIATE CHEMISTRY 



The valence of carbon is almost always four. This is clearly 

 seen in C IV O 2 n and C IV H 4 T . In a few compounds, of which CO is 

 the commonest, carbon is bivalent. 



Carbon Tetrachloride CC1 4 . This compound is manu- 

 factured by leading dry chlorine into carbon disulphide, in which 

 a little iodine (contact agent) is dissolved : 



3C1 2 - CC1 4 



On distilling the resulting mixture, the carbon tetrachloride 

 (b.-p. 77) passes off and is condensed, while the sulphur mono- 

 chloride S 2 C1 2 (b.-p. 136) remains. 



Carbon tetrachloride is a colorless liquid. It dissolves fats 

 and tars and other organic compounds, and has the advantage 

 over benzine and gasoline of being non-inflammable. It is there- 

 fore used in taking the grease out of wool, linen cloth, oil-bearing 

 seeds, and bones. Many liquids sold for dry cleaning and remov- 

 ing stains from clothing, gloves, etc., consist of carbon tetrachlo- 

 ride diluted with a cheaper material, such as benzine. Although 

 the proportion of such material originally added may be insuffi- 

 cient to render the mixture inflammable or explosive, the risk 

 exists that evaporation of the more volatile carbon tetrachloride 

 may eventually bring the composition of the residue into the dan- 

 gerous region. Products containing no benzine are therefore to 

 be preferred. Many fire extinguishers also contain a liquid which 

 is mainly carbon tetrachloride. 



Carbides and the Electric Furnace. Chemical actions 

 which proceed only at very high temperatures are most economic- 

 ally carried out by using electricity as the source of heat. In 

 such cases the electricity has no electrolytic or other chemical 

 action. There are two types of electric furnaces. In the making 

 of graphite (p. 330) and of carbon disulphide (p. 255), which 

 illustrates one of them, the resistance of the carbon furnishes the 

 occasion for the rise in temperature. 



Of the same type is the furnace used for making carborundum 



