158 APPLIED SCIENCE 



175. Hydrocarbons. The many compounds of carbon 

 and hydrogen are called hydrocarbons. Carbon unites with 

 elements, particularly metals, to form carbides, such as cal- 

 cium carbide and silicon carbide. Calcium carbide is made 

 by heating lime and coke or coal in an electric furnace. It 

 is a brittle, dark gray, crystalline solid which forms acety- 

 lene gas on the addition of water. 



CaC 2 + 2H 2 C 2 H 2 + Ca(OH) 2 



Calcium Water Acetylene Calcium 



Carbide Hydroxide 



176. Flame. When gases are burned a light is given off. 

 This light is called a flame. Flame is due to the combina- 

 tion of a gas with the oxygen of the air. A flame may be 

 luminous, as in the case of an ordinary gas light, or it may 

 be non-luminous, as in the case of the blue flame of a gas- 

 burner. The luminosity of a flame is due to the glowing 

 of small particles of carbon. A yellow flame is caused by 

 incomplete combustion. 



177. Compounds of Carbons. The following are the 

 names, symbols, and uses of some of the most important 

 classes of carbon compounds: 



Class 



of Compounds Composition Use 



Carbohydrates Compound of carbon, hydro- Sugars 



gen, and oxygen, the last Starches 



two in the proportion to Cellulose 

 form water. 



Alcohols Compound of carbon and hy- Wood alcohol 



drogen with an OH group. Grain alcohol 

 C 2 H S .OH, ordinary spir- 

 its of alcohol, 



