224 SECRETS OF EARTH AND SEA 



diverse ways invented by human ingenuity. Thus 

 natural gas — superseded by distilled coal-gas — has served 

 for fuel and for illumination : refined petroleum serves not 

 only for those uses in general, but as the special source of 

 power in the engines of motor-cars and aeroplanes. A 

 wonderful solid crystalline wax-like substance, paraffin, 

 as white as snow, is distilled in enormous quantities 

 (nearly three million tons a year) from " bituminous shale " 

 or " oil-shale " in this country alone. It can be obtained 

 in soft (vaseline) and liquid forms, and in fact the " paraffin 

 series " recognized by chemists starts from the gas 

 " methane," or marsh-gas, and comprises some thirty kinds, 

 leading from gas to volatile liquids, thence to viscid liquids, 

 to butter-like solids, and up to hard crystalline substances 

 which melt only at the temperature of boiling water. 

 Endless chemical manufacturing industries — e.g., those of 

 dye-stuffs and explosives — depend upon the chemical 

 treatment of these paraffins and of various bodies obtained 

 as secondary products in their preparation. Benzine and 

 aniline are chiefly obtained from coal-tar. The oils and 

 waxes of quasi-mineral origin have a great advantage over 

 vegetable and animal oils in many uses, since they are not 

 liable to become " rancid " ; that is to say, to decompose 

 owing to the action on them of bacteria. A marked 

 difference between the paraffins (often distinguished, 

 together with the " olefines," as "mineral" oils) and the 

 oils and fats found in living plants and animals is that they 

 do not M saponify " ; that is to say, they do not form those 

 combinations with alkalis and other bases which are called 

 " soaps," nor can they serve as food to man or any other 

 animal. They are not acted on by the digestive juices. 



From ancient times natural deposits or outpourings of 

 " bitumens " have been known and used by mankind. 

 The Assyrians and other early peoples of the East used 

 " asphalt " (translated by the word " slime " in the English 



