1920] RURAL ENGINEERING. 389 



account the nbove factors, is P=H' *R*'X0.12C— 0.3S, In this formula, P= 

 the resultant lateral pressure in pounds per square inch; R=the rate of fill 

 In feet per hour; II=the head of concrete fill; C=the percentage by volume 

 of cement in the combined fine and coarse aggregate; and S=the consistency 

 in inches of slump. 



The vertical pressure is obtained by adding 0.25H to the value of P as found 

 above, except when the inside distance between the vertical sides of the form 

 Is greater than one-half of the depth of fill. Then the vaFiie should be taken 

 as equal to the weight of the concrete. The value for H, the head of concrete. 

 to be used in the formula, should not be greater than one-half the rate of fill, 

 except where agitation is vigorous and continuous in a sloppy mix, when this 

 ratio may be taken up to three-fourths. 



Pressure of g:reen concrete against forms, E. B. Smith {Concrete [Detroit, 

 ilich.], 16 (1920), No. 3, pp. 158-161, fujs. 5).— This is a less detailed report of 

 tlie experiments noted above. 



Determining bitumen content in bituminous concrete, II, M. Gbeen 

 {Enyin. Neios-Rec, 84 (1920), No. 18, pp. 871, 872).— On the basis of studies con- 

 ducted at the Texas Agricultural and Mechanical College a method of pro- 

 portioning the bitumen content in bitumhious concrete is described, whicli 

 takes into consideration surface area of aggregate, consistency of bituminous 

 cement, absorption of aggr(>gate, and spocilic gravity of aggregate. 



Chemistry of materials of the machine and building industries, R. B. 

 Leighou (Neio York: Mc(Jraw-.Hill Boole Co., hic, 1917, pp. XV-\-U9, figs. 75). — 

 The object of this book is to supply information concerning the cliemical 

 properties of the materials commonly employed in building construction and 

 equipment and in machinery construction and operation. 



The following chapters are included: Water for steam genei'ation ; fuels; 

 refractory materials for furnaces ; iron and steel.; the cori'osion of iron and 

 steel; the nonferrous metals; the nonferrous alloys; solder; foundry sands; 

 building stones ; lime and gypsum products ; Portland cement ; clay and clay 

 products; paints, varnishes, stains, and fillers; lubricants; glue; rubber; 

 electrical insulating materials; primary electric cells; secondary cells; and 

 hydrometry. 



Internal-combustion engine fuels, E. W. Dean (Jour. Soc. Automotive 

 Engin., 6 (1920), No. 2, pp. 107-117, fiyfi. iS).— The manufacture and testing of 

 Internal combustion fuels is described in some detail, with particular ref- 

 erence to their use in tractor engines. 



Report of the Inter-Departmental Committee on various matters con- 

 cerning the production and utilization of alcohol for power and traction 

 purposes, B. Reuwood (London: Interdept. Com. Alcohol Motor Fuel, 1919, pp. 

 8). — The results of an investigation into the use of alcohol for power and trac- 

 tion purposes are reported, and recommendations as to governmental action 

 are given. 



Tractor experience in Kentucky, W. D. Nichoixs (Kentucky Sta. Bui. 222 

 (1919), pp. 47-68, figs. 4)- — This bulletin reports the experience of tractor 

 owners on 320 farms in Kentucky in 1918. 



Seventy-one per cent of the tractor owners, on farms averaging 493 acres in 

 edze, reported a profitable Investment. A unit of work with the tractor cost 

 more on small farms than on large farms. The reports indicate that the 

 smallest size of farm on which a tractor may be used economically is about 

 175 acres. The 3-plow size of tractor was recommended by a great majority 

 of the owners reporting on this point. The average number of days of work 

 reported was 49.5 per farm for 12 months. Adding to this the custom work 

 done, the work averaged 55 days for the year. The average number of acres 



