191-0] 



RURAL ENGINEERING. 



891 



mixture ?dvinp the best economy at a lii;:h temperature was a leaner mixture 

 than that givini; the best economy at a lower temperature. 



Kerosene as u tractor fuel, J. A. Skcor (Jour. .S'or-. Automotive Engin., 7 

 (1920), No. 2, pp. I'fO-l.'flt. l.'iG. fig. 1). — Recent data and developments on the use 

 of kerosene as a fuel for tractors are summarized. 



Operation and care of vehicle-type batteries ( U. tS'. Dcpt. Com., Bur. 

 Standards Circ. 92 (1920), pp. 9//, pis. 9, figs. ^3). — This is a manual of informa- 

 tion and instruction, prepared by A. L. Pearson and G. W. Vinal, on the opera- 

 tion and care of batteries for mechanically propelled vehicles. 



Geometry of belt drives, G. Du>fing (Ztschr. Ver. Deut. Ingen., 63 (1919), 

 pp. 951-956; abs. in Sci. Abs., Sect. B— Elect. Engin., 23 (1920), Xo. 266, p. 79).— 

 It is pointed out that the geometrical form of a belt drive consi.sts of two curves 

 touching two given circles. These curves become straight lines only in the 

 case of a perpendicular drive between pulleys of equal diameter. Simple 

 formulas are developed by the process of progressive approximations for the 

 main geometrical quantities of a belt drive, namely, arc length, sag, etc. It is 

 assumed that the form of the center line of the belt at rest is the ela.stic ex- 

 tensible catenary, neglecting the resistance to bending and assuming a linear law 

 of extension. The accuracy of the formulas is demonstrated by numerical ex- 

 amples and is shown to he ample for all practical requirements. 



Wire belts with paper driving surface, H. Mittermayr (Ztschr. Ver. Deut. 

 Ingin., 63 (1919), pp. 1057-1061; abs. in Sci. Abs., Sect. B— Elect. Engin., 23 

 (1920), No. 266, pp. 79-81, figs. 2).— Belts are described consisting of flat wound 

 wire spirals with alternately right and left-hand lead coupled together by cross 

 pins. Paper yarn is wound between the spirals, giving the belt a soft running 

 surface and securing the adhesion required for power transmission. 



Tests were made to determine the capability of these belts to transmit the 

 same power as leather belts when running on the same pulleys. The tests 

 showed no appreciable slip between belt and pulley until the load became ex- 

 cessive. Three degrees of slipping were then observed, namely, slight waves, 

 sharp flickering movements, and a swinging of the whole span of the belt. A 

 little wax increased the power transmitted by the belt, but an excess caused 

 unsteady running by accumulating on the pulley. It was found that the possible 

 power transmission increased with the distance between axes, which must not 

 be less than a certain minimum if favorable conditions are to be obtained. 

 About the same transmission was obtained with wooden as with iron pulleys. 

 Thicker belts of this construction employed coils of greater pitch and relatively 

 smaller adhesion surface, so that the permissible belt tension per inch width 

 increased slowly or even decreased with increasing belt thickness. 



The maximum permissible tension in pounds per inch of belt width for a belt 

 of medium thickness was Tound to vary approximately as shown in the follow- 

 ing table: 



Permissible belt tension per inch width. 



