HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 463 



traces of substances having a higher boiling-point are simultaneously 

 volatilized with the distilling substance. 



FIG. 



Flasks arranged for fractional distillation. 



For fractional distillation of small quantities of liquids as well as 

 for the determination of boiling-points, flasks arranged like those 

 shown in Fig. 69 may be used. 



Properties of hydrocarbons. There are no other two elements 

 which combine together in so many proportions as carbon and hydro- 

 gen. Several hundred hydrocarbons are known, many of which 

 form either homologous series or are metameric or polymeric. 



Hydrocarbons occur either as gases, liquids, or solids. If the mole- 

 cule contains not over 4 atoms of carbon, the compound is generally 

 a gas at the ordinary temperature ; if it contains from 4 to 10 or 12 

 atoms of carbon, it is a liquid ; and if it contains a yet higher number 

 of carbon atoms, it is generally a solid. 



All hydrocarbons may be volatilized without decomposition, all 

 are colorless substances, and many have a peculiar and often charac- 

 teristic odor ; they are generally insoluble in water but soluble in 

 alcohol, ether, disulphide of carbon, etc. 



