294 CHEMICAL DISCOVERY AND INVENTION 



produced by burning is instantly available, and with a properly 

 constructed furnace no smoke need be produced. There are 

 also no ashes to be cleared out from the furnace and removed by 

 the stoker. 



In order to burn a thick liquid like natural petroleum it is 

 necessary to distribute it in the form of spray, and a great deal 

 of ingenuity has been expended in contriving burners for this 

 purpose. In many forms of " atomiser " the oil is sprayed by 

 means of a jet of steam into a chamber where it finds the air 

 requisite for combustion, and by regulation of the oil supply a 

 blue smokeless or a smoky flame may be produced at pleasure. 

 In other forms of jet the oil is pulverised by being forced 

 under pressure through a small orifice of peculiar construc- 

 tion. 



The number of distinct substances obtained from petroleum is 

 very large, but reference to the table (pp. 292-293) will simplify 

 the classification and enumeration of these products. 



The gases associated with petroleum in nature consist chiefly 

 of methane or marsh-gas mixed with small quantities of other 

 hydrocarbons, together with a little nitrogen and traces of 

 hydrogen, carbon dioxide, and sometimes sulphuretted hydrogen. 

 This wonderful natural supply of gaseous fuel was for many 

 years allowed to escape in the neighbourhood of the American 

 oil wells, but this deplorable waste was ultimately put an end 

 to, and for the last thirty years or more natural gas has been 

 applied, not only to the lighting of towns, but in the manufacture 

 of steel and glass, and generally for the production of heat on a 

 large scale. 



From petroleum a number of liquid products are obtained 

 which are indicated in the table by the letters A, B, C, and D. 

 Every one of these is, however, a mixture of several compounds, 

 olefmes as well as paraffins, and may for special purposes be 

 further subdivided by distillation. 



A includes a small quantity of very volatile liquid which can 

 only be retained in the liquid state by pressure or cold. This is 

 sometimes used in surgery as a local anaesthetic for cooling the 

 surface to which it is applied. The greater part of A is used 

 under the names gasoline, light benzine, or benzoline for producing 

 " air-gas " employed in lighting country houses. 



B is benzine, used extensively as motor spirit, also for cleaning 

 purposes and as a solvent. 



