CARBON. 79 



Neither form of carbon is fusible, volatile, or soluble in any 

 of the common solvents. 



Carbon is a quadrivalent element; it has little affinity for 

 metals, but combines with many of the non-metals, chiefly with 

 oxygen, hydrogen, and nitrogen, forming the organic substances. 



Tests for carbon. 



1. Most non-volatile (organic) substances containing carbon, 

 blacken when heated on platinum foil. 



2. The product of combustion of carbon (or of combustible 

 matter containing it), C0 2 , renders lime-water turbid. 



Carbon dioxide, C0 2 = 44. (Formerly named carbonic acid, or 

 anhydrous carbonic acid.) This compound is always formed during 

 the combustion of carbon or of organic matter; also during the 

 decay (slow combustion), fermentation, and putrefaction (pro- 

 cesses of decomposition) of organic matter; it is constantly pro- 

 duced in the animal system, exhaled from the lungs, and given 

 off through the skin. Many spring waters contain considerable 

 quantities of the gas, one single spring in Nauheim, Germany, 

 liberating as much as 3000 pounds of carbon dioxide a day. 



Many carbonates are decomposed by heating into oxides of 

 the metals and carbon dioxide. 



Lime-burning is such a process of decomposition : 



CaCO, = CaO + CO, 



Calcium Calcium 



carbonate. oxide 





Another method for the generation of carbon dioxide is the 

 decomposition of any carbonate by an acid : 



CaCO 3 -f 2HC1 = CaCl 2 + H 2 O + CO 2 . 



Calcium Hydrochloric Calcium 



carbonate. acid. chloride. 



Carbon dioxide is a colorless, odorless gas, having a faint acid 

 taste. By a pressure of 38 atmospheres, at a temperature of 

 C., carbon dioxide is converted into a colorless liquid, which 

 by intense cold ( 79) may be converted into a white, solid, 

 crystalline, snow-like substance. The specific gravity of car- 

 bon dioxide is 1.524; it is consequently about one-half heavier 

 than atmospheric air. 



