308 



TwENTY-SIiVENTH ANNUAL REPORT 



TABLE XXVII. 



PRONY BRAKE TESTS OF COMMERCIAL, ENGINE AT CONTI- 

 NENTAL, ARIZONA 



The important conclusions to be drawn from these tests are : 



1. Both the capacity and the fuel economy of oil engines decrease 

 with altitude. 



2. The engines built in California should be rated more liberally; 

 they should have some reserve power at an altitude of 2800 feet. 



3. The clearance space should be reduced as the altitude increases. 



4. Tops fuel oil of 40° to 44° B. gravity can be burned perfectly 

 in well-designed 4-cycle engines and will give more power per gallon 

 than engine distillate (50° B.) 



GUARANTEES FOR PUMPING MACHINERY 



A common difficulty in the purchase of an engine and pump is in 

 securing a satisfactory guarantee. Guarantees in the past have been 

 of such a character that it was impossible for the purchaser to ascertain 

 whether or not the plant fulfilled the guarantees. Many selling agents, 

 usually transients in the State, have taken advantage of this fact by 

 iv.aking guarantees which could not be fulfilled. Tests could not be 

 made and the impositions have not been discovered. This office has 

 prepared a standard form of guarantee and has requested dealers in 

 pumping machinery in Arizona to adopt it. With a very few exceptions 

 they have consented. 



CONCRETE WATER AND OIL TANKS 



Several times in the past farmers have requested assistance in de- 

 signing concrete tanks for holding water or engine fuel oil. Some of 

 the tanks thus built have proven very successful and when once in use 

 and made water-tight, they are far more durable than the more common 

 galvanized iron tanks. The two problems involved are those of rein- 

 forcement and water-tightness. The first is capable of exact computa- 

 tion and the second requires only expertness in the proportioning and 

 mixing of the concrete, a task which should not be undertaken alone by 

 the ordinary farmer, though he might succeed with other forms of 

 concrete construction. 



