398 BcLLKTiN 92 



toflay. Electric power was used in a few plants. These early plants 

 were described, with tests of their operation, in two bulletins of this 

 Station.* The distillate plants possessed a great advantage over the 

 steam plants in the cost of attendance, an item which in the small steam 

 plants outweighed the diliierence in fuel costs. In 1910 it appeared that 

 the most feasible power for pumping was to be obtained from central 

 power plants burning boiler fuel oil. 



The available gasoline supply was quickly absorbed by the rapid 

 increase in the number of automobiles and motor trucks. The standard 

 of commercial gasoline was reduced from 68° Baume to 60° Baume and 

 consequently the supply of engine distillate or its quality had to be 

 reduced. California engine distillate dropped from 55° B. to 50° B., 

 and has since been reduced as low as 43°. California pump irrigators 

 have continued to use the refined distillate to the present day, partly 

 because of their comparative proximity to the refineries and consequent 

 light freight charges. 



In 1912, it was found that the cheap, abundant distillates of 37° 

 to 44" Baume gravity, costing 2H cents per gallon in carloads, f.o.b. 

 Los Angeles and nearby points, could be utilized for fuel by slight 

 modifications of the fuel mixers of the standard gasoline engines. The 

 modifications consist of preheating the air or a part of the air and 

 introducing a small amount of hot water into the fuel mixture. Strong, 

 high-tension magnetos, also, have a great advantage over low-tension 

 magnetos or wet batteries in burning this fuel, and another aid to good 

 combustion that has been used to some extent is lengthening the con- 

 necting rod so as to increase the compression pressure. The cheap 

 distillates were obtained at first by "topi)ing" heavy crudes in order 

 better to fit them for use in locomotives ; this process gave a low flash 

 l)oint to the "tops". Later, somewhat similar oils were obtained as 

 straight cuts in the refining process. These products were called tops 

 or gas oil, and were adopted widely in Arizona. Being unrefined, they 

 have always taken the same freight rate as boiler fuel oil and other 

 unrefined fuel oils. Lender the stimulus of the cheap tops or gas oil, 

 l)ump irrigation has grown by leaps and l)ounds since 1912. It is prob- 

 able that the numl)er of plants has increased ten-t(^lfl and the amount of 

 water pumped a hundred-fold. The area of puinji irrigation has spread 



*Hul. -lit. Co'st of runipins for Irrigation, and Hiil. di. (Jrouinlwator Siiiijily ami Trrieation 

 in the Rillito Valley, Chapter VII. Since 1910 two additional bulletins for pump irriirators have 

 been issued: H\il. 71 on Care and Operation of Gasoline Engines and Bui. 7-1 on Oil Kngines for 

 I'uinp Irrigation and the Cost of Pumping. 



