288 EXPERIMENT STATION RECORD. [Vol.43 



At lower speeds the power was influenced A-ery little by variation in ratios 

 of mixture between rather wide limits. Practically no variation appeared up 

 to 400 r. p. m. throughout the whole range of workable mixtures. At 500 

 r. p. m. it was possible to operate the engine on mixtures of less than 8 lbs. 

 of air per pound of fuel, although at a very marked sacrifice of power. From 

 9.5 lbs. up to over 17 lbs. the power remained practically constant. At GOO 

 r. p. m. a drop in power was noticeable with air quantities exceeding 14 to 15 

 lbs. per pound of fuel. At higher speeds the range of constant and optimum 

 power became narrower until at 900 and 1,000 r. p. m. there was a decided peak 

 at about 10.5 to 11 lbs. of air per pound of fuel. 



The influence of increased richness of mixture on fuel economy was uniformly 

 toward a greater fuel consumption. At higher speeds very lean mixtures like- 

 wise showed an increase in the fuel consumption per brake-horsepower. The 

 general effect of air heating was to reduce power, but the fuel economy, 

 especially at the higher speeds, was not affected very much by variations in 

 the air temperature. The fuel economy at a ratio of 12 : 1 varied but little 

 with the speed from 400 to 1,000 r. p. m. However, a fuel economy fully 20 

 to 25 per cent better than that at 12 : 1 was obtained by using weaker mixtures. 



It is concluded that while rich mixtures and low temperatures give maxi-' 

 mum power, leaner mixtures and higher temperatures are conducive to the 

 greatest fuel economy. It is noted that the greatest economy occurred at from 

 speeds of from 400 to 600 r. p. m. The conclusion is also drawn, in connection 

 with increased air temperature, that the mixture just prior to combustion, 

 although at a slightly different temperature, is almost in the same state of 

 evaporation in all cases. 



The problem of good valves for the tractor, W. C. Willard (Agrimotor, 

 3 {1920), No. Jf, pp. 112, 114, figs. 5). — This is a brief treatise summarizing ex- 

 perience in the design and manufacture of valves for tractor engines. 



Comparing tractor speeds with power, C. E. Frudden {Agrimotor, 3 {1920), 

 No. Jf, p. 60, fig. 1). — Data are reported to show the effect of higher plowing 

 speeds upon the power required from the tractor engine. 



Graphic data show the relation between power, number of plows, and speed 

 of travel as expressed by the formula, horsepower=-NXSX3.6, in which the 

 horsepower is expressed as brake-horsepower of the engine ; N equals the 

 number of 14-in. plows ; S equals speed in miles per hour ; and 3.6 equals an 

 experimental factor. "According to- this formula ... a tractor engine of 25 

 b. h. p. can pull two plows at 3.5 miles per hour, three plows at 2.33 miles 

 per hour, or four plows at 1.75 miles per hour. Or, on the same basis, the 

 power required for general satisfaction when pulling three 14-in. plows will 

 vary as follows: 21.6 h. p. for three plows at 2 miles per hour, 27 h. p. for 

 three plows at 2J miles per hour, 32.4 h. p. for three plows at 3 miles per hour, 

 or 37.8 h. p. for three plows at 3^ miles per hour. . . . 



" If, as is often said, the tendency is toward higher plowing speeds, tractors 

 will require larger engines in proportion to the increase in speed plus the 

 deficiency now existing in a great many outfits to bring them up to the 

 standards here set forth." 



The design of light tractor plows, J. J. Bergin {Impl. and Mach. Rev., 45 

 (1920), No. 539, pp. 1632-1634).— The author analyzes the design of light tractor 

 plows with reference to conditions in Ireland, and presents the following speci- 

 fications for what he considers to be the model design for a tractor plow suited 

 to small and medium farms and light and medium land: 



(1) Weight about 3^ cwt. ; (2) to turn 2 furrows 9 to 10 in. wide; (3) 

 fitted with digging or semidigging breasts and have tail pieces fitted; (4) 



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