FUEL FOR GAS TRACTORS 121 



the naphthas from 52 to 80 Baume are commonly grouped to- 

 gether to form a yield of about 10 per cent, of commercial 

 gasoline. The gasoline of to-day is the " Naphtha A" of 

 ten years ago, while true gasoline is rare and issued almost 

 solely for aeroplanes, racing automobiles and other extreme 

 purposes. Distillates of 52 to 58 Baume, which are now sold 

 as benzine to the paint trade, become naphtha to the owner 

 of a motor boat. 



There are two ways in which fuel of a certain specific gravity 

 can be obtained. One way is to distil into it only that fraction 

 of crude oil which approximates the desired density, thus 

 gaining a very uniform product. The other is to mix together 

 distillates of high and low gravity so as to obtain -a mean some- 

 where near what is required. It is obvious that at any given 

 temperature a portion of the latter oil will evaporate at a much 

 more rapid rate than the remainder, so that the oil left in the 

 reservoir will continue to grow heavier. The ideal fuel is the 

 one which is uniform in composition, as it is equally obvious 

 that a carbureter adjusted to handle the lighter constituents 

 will be unable to handle the heavier parts without readjustment. 

 Uniform fuel would require but one adjustment of the mixture 

 for any given condition of work. The weight or Baume gravity 

 of a liquid fuel is not a reliable indication of its composition 

 i. e. 9 its vaporizing qualities. Nothing but fractional distilla- 

 tion will disclose whether or not heavy and light products have 

 been mixed. 



If commercial fuel oils were pure chemical compounds it 

 would be a much simpler process than at present to supply the 

 proper conditions of temperature and mixture to insure perfect 

 combustion. But we have seen that Pennsylvania crude oil, 

 which weighs about the same per gallon as ordinary engine 

 kerosene, is composed of substances varying from solid residues 

 to liquids which vaporize at low temperatures. From this 

 it is evident that the amount of uniform fuel of high Baum6 

 gravity which could be supplied was always limited. 



