586 EXPERIMENT STATION EECOED. [Vol.41 



per cent can be reached, which decreases to So per cent for high-speed engines, 

 and for extreme speeds may be even lower. These values presuppose high- 

 grade engines with mechanically operated valves." 



With reference to the effect of high altitudes, it is stated that the horse- 

 power rating of a Diesel engine decreases 3 per cent for every 1,000 ft. of 

 added altitude. 



" The high commercial value of the Diesel engine lies in its unsurpassed 

 fuel economy and in its ability to burn low-priced liquid fuels with high 

 boiling points. This great fuel economy is not confined merely to medium or 

 large sized units, for the smallest engine has nearly the same fuel economy as 

 the largest." 



Data are given which indicate " that although the absolute fuel price for 

 fuel oil may be several times higher than that of coal in the same market, 

 power may be generated more cheaply with the Diesel than with the steam 

 engine." 



The disadvantages of Diesel engines are stated as high consumption of 

 lubricating oil and high installation cost, including heavy foundations. 



Leng'th. of motor truck stop varies inversely as braked load {Engin. News- 

 Rec, 81 {1918), No. 18, pp. 799, 800).— Braking tests conducted by G. W. Smith 

 of motor trucks and automobiles on a concrete road having a thin coating of 

 oily dust showed the advantage of concentrating a large proportion of the load 

 on the braked wheels. It was found that the coefficient of friction for rubber 

 tires on dry paving was from 0.475 to 0.53. With a uniform speed of 20 miles 

 per hour the shortest stops were made by trucks having a relatively high per- 

 centage of the total weight carried by the rear or braked wheels, while the 

 longest stops were made by a touring car with relatively light wheel loading. 



A second set of tests by L. D. Hemman, in which solid rubber tires were used 

 for 3, 2, and 0.5 ton trucks and pneumatic tires for the automobile, showed that 

 skidding of light trucks took place on wet asphalt when the brakes were applied 

 with a uniform speed of 15 miles per hour. When the asphalt was very wet 

 with a slight coating of sloppy snow, the skidding tendency of the lighter ma- 

 chines was greatly increased, while the larger trucks skidded only 2 or 3 feet 

 out of line. 



Important and neglected features of tire maintenance, A. F. Masuby 

 (Engin. Neivs-Rec, 82 (1919), No. 26, pp. 1262-1264, figs. 5).— Data are re- 

 ported showing that for large motor trucks tire cost and fuel cost are normally 

 about equal. On lighter trucks the tire cost is slightly less than the fuel cost 

 unless pneumatic tires are used, when the tire cost will slighly exceed the fuel 

 cost. In this connection a warning is given against overloading, overspeeding, 

 neglecting ciits and tears, spinning, skidding, and sliding the wheels, and wheel 

 misalignment. 



Directory and specifications of farm tractors (Farm ilachmery. No. 1^42- 

 14Jf3 (1919), pp. 16. iOS).— This directory contains data on 253 farm tractors of 

 170 different makes. 



Mole plows worked by horses (Jour. Bd. Agr. [London], 25 (1918), No. 1, pp. 

 36-40, figs. 5). — Drawings showing the details of mole plows in use for draining 

 land quickly are given. 



A barn for the small farm, H. H. Musselman (Michigan Sta. Quart. BuL, 

 2 (1919), No. 1, pp. 32-34, figs. 2). — A ground plan and some construction de- 

 tails for a barn for a small farm keeping fi-om 2 to 4 horses and 10 to 15 cows 

 are given. 



Practical hog' houses for Indiana, C. A. Norm an and J. W. Schwab (Piirdvc 

 Univ., Dept. Agr. Ext. Bui. 76 (1918), pp. 8, figs, 12). — This bulletin gives draw- 



