Arizona Agricultural Experiment Station 599 



FUEL OILS FOR PUMPING 



The results of studies of fuel oils, both in the laboratory 

 and in use at pumping plants, have been published as Bulletin 

 92, under the title "The Supply, the Price, and the Quality 

 of Fuel Oils for Pump Irrigation." This bulletin has proved 

 to be of much value to fuel oil users in obtaining their supply 

 for this season, and has done much to improve the quality of 

 the fuel oils shipped into the State. Furthermore, it has di- 

 rected the attention of refining companies of the Oklahoma and 

 north Texas oil fields to this important market for moderately 

 heavy distillates, with the result that many of them are now 

 furnishing an excellent engine fuel oil, which they have named 

 "Arizona gas oil." The bulletin has assisted, also, in the set- 

 tlement of freight claims arising from confusion in the classi- 

 fication of distillation products. 



Additional tests of fuel oils are being made from time to 

 time as samples are submitted. Two new flash-point testers 

 have been added to the equipment, a Tagliabue tester for light 

 fuel oils and a Pensky-Martens tester for heavy oils. 



STREAM-FLOW MEASUREMENTS 



The Irrigation Department is maintaining fourteen stream- 

 gaging stations in Cochise County, two in Pima County, and 

 several in Pinal County. The records of stream flow are ob- 

 tained with special reference to source, distribution in time, and 

 the seepage losses which go to recharge the groundwater 

 supplies. 



EFFECTS OF THE TRANSPIRATION OF TREES ON THE 

 GROUNDWATER SUPPLY 



Seven years ago it was suggested that the loss of water 

 through transpiration of trees constitutes the largest ground- 

 water loss in many valleys of southern Arizona. If, therefore, 

 the transpiration loss could be measured, it would provide a 

 means of estimating the groundwater supplies in such valleys 

 as the Santa Cruz and the San Pedro. In 1916, investigations to 

 determine the relation of tree transpiration to groundwater 

 were initiated at Redington, where exceptionally large and 

 uniform forests of mesquite and cottonwood exist. The inves- 

 tigations were interrupted by the war. They were again started 

 in February of this year and results of much value are being 

 obtained. 



