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 natural gas superseded by distilled coal-gas has served 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 "defines," as "mineral" oils) and the 

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

 do not " 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 



