LUBRICANTS 303 



at least a gas engine fuel, which has its constituents guaran- 

 teed, in order that the purchaser may obtain whatever grade 

 he wants for his particular purpose. Density alone is not the 

 best test; a fractional distillation test should also be made. 



It is important in using a gas engine to have the proper 

 amount of air mixed with the gasoline vapor. Too much 

 air dilutes the mixture and reduces the power. Too little 

 air does not permit of complete combustion, and this also 

 reduces the power and causes waste of fuel. Gasoline being 

 a mixture of hydrocarbons burns to carbon dioxide and 

 water when there is enough oxygen present. On this account 

 the exhaustion should not take place indoors for the large 

 quantities of carbon dioxide eliminated are detrimental 

 to health. The following may be taken as a typical reaction : 



2C 8 Hi 8 +250 2 = I6CO2 + 18H 2 0. 



This means that one gallon of gasoline, assuming it to be 

 octane, CsHi 8 , 64.8° Be., will require about 1180 cubic feet 

 of air at 62° F. When insufficient oxygen is present the 

 products of combustion are different, and include carbon. 

 The maximum amount of heat, and consequently power, is 

 developed only when combustion is complete. 



222. Lubricants. — The purpose of a lubricating oil is to 

 reduce friction between moving surfaces, and it should 

 have sufficient "body" or viscosity not to be squeezed out 

 from between the surfaces. Too viscous an oil will cause 

 friction of the oil itself and reduce efficiency. A lubricating 

 oil should not be so volatile that it will not last under the 

 temperature to which it is subjected. The flash test is useful 

 in determining this point. Neither should an oil have any 

 free acid present, such as sulphuric acid if a hydrocarbon oil ; 

 fatty acid, usually stearic, if an animal or vegetable oil. The 

 free acid corrodes the bearings. 



From the tar or residuum left in the first distillation of crude 

 petroleum there are obtained (Section 220) a series of lubri- 

 cating oils which are of excellent character, and better 

 suited for most machinery than animal or vegetable oils, 

 though for some purposes the latter are better. 



