390 EXPERIMENT STATION RECORD. [Vol.48 



of land plowed per day was 6.26 for the 2-plow tractor, 7.77 for the 3-plow» 

 and 10.9 for those of the 4-plow size and larger. The use of the tractor 

 enabled these farmers to reduce the number of work animals from an aver- 

 age of 10.6 to 8.7. 



The amount of fuel used per acre for plowing with tractors of all sizes 

 averaged 2.9 gals, and the amount of lubricating oil about 0.2 gal. per acre. 

 The life of the tractors as estimated by 213 owners was 7.3 years. The cost 

 per acre for plowing with a tractor is about $1.70. This includes repairs, 

 depreciation, interest, taxes, insurance, fuel, lubricants, and labor. Of 1.51 of 

 these tractors used for cutting silage, all but 8 were reported as furnishing 

 ample power for that purpose. Of the traOtor owners doing custom work a 

 majority expressed the opinion that it does not pay. 



Notes on the tractor in the United States, O. Peeh:s {Brasil Agr., 4 {1919), 

 Nos. 6, pp. 153-159; 7, pp. 188-193; 8, pp. 226-228, figs. 9).— In this paper, a 

 contribution from the Georgia State College of Agriculture, practice in the 

 design, operation, testing, and practical use of tractors in the United States is 

 reviewed. 



The tractor (Topeka, Kans.: Capper Farm Press, 3. ecL, rev. and enl. [1920], 

 pp. 56, figs. 39). — This is a general summary of data on the practical use of the 

 tractor. 



Tractor ploveing speeds, O. B. Zimmerman (Jour. Soc. Automotive Engin., 

 6 (1920), No. 2, pp. 133-137, figs. iO).— Considerable data on tractor plowing 

 speeds are summarized, witli particular reference to the economic side of the 

 question. 



It is concluded that, placed upon a comparable basis and with reasonable 

 assumptions supplementing the carefully prepared and conducted experiments 

 used, the most economical plowing speeds are unquestionably below 3 miles per 

 hour, the cost rising rapidly from about 2 miles per hour. " If plows are de- 

 signed to meet higher speeds they can lielp only in reducing the greatly in- 

 creased costs at the higher speeds, but they can not by any means veer the 

 economical point above 3 miles per hour. The argument for better breaking 

 up of the soil at the higher speeds is heavily paid for, and it is more economical 

 to perform the operation of harrowing either separately or behind the plows 

 than to try to accomplish it by rapid plowing. To attain the very best results 

 with the plowing outfits, speed ratios of plow gearing and throttle should cover 

 the ranges from If to 3 miles per hour. This would permit the most flexible 

 ranges to meet the various soil resistances. 



" It appears that in heavy land and in plowing up to 8 in. in depth with small 

 tractors, greater acreage would be attained by the use of 10 or 12-in. Instead of 

 14-in. plow bottoms. ... A better adjustment of cutting width is also pos- 

 sible." 



The time required to plow one acre is tabulated from tests with relation to 

 the number of plows pulled, as follows: Heavy land, 2 plows 1.212 hours per 

 acre, .3 plows 1.095 hours, 4 plows 1 hour, and 5 plows 0.926 hour ; on light 

 land, 2 plows 0.643 hour, 3 plows 0.563 hour, 4 plows 0.560 hour, 5 plows 0.462 

 hour, 6 plows 0.426 hour, and 7 plows 0.4 hour. 



The installation of dust-collecting fans on thrashing machines for the 

 prevention of explosions and fires and for grain cleaning, H. E. Roetue, jb., 

 and E. N. Bates (U. S. Dept. Agr., Dept. Circ. 98 (1920), pp. 11, figs, ii).— This 

 circular deals with the general features in the design, cx)nstruction, and instal- 

 lation of fans for the collection of dust from thrashing machines to prevent dust 

 explosions. A number of the most effective and satisfactory fans are illustrated 

 and discussed. 



