19161 RURAL ENGINEERING. 791 



" With the relative volucies of fine and coarse aggregate fixed, the com- 

 pressive strength of a concrete increases directly, but not in a proportionate 

 ratio as the cement content. An increase in the ratio of cement to total fine 

 and coarse aggregates when the relative proportions of the latter are not 

 fixed does not necessarily result in an increase in strength, but may give even 

 a lower strength. 



" The compressive strength of concrete composed of given materials com- 

 bined in definite proportions and fabricated and exposed under given condi- 

 tions can be determined only by testing the concrete actually prepared and 

 treated in the prescribed manner. . . . The compressive strength of most 

 concretes as commercially made can be increased 25 to 100 per cent or more by 

 employing rigid inspection, which will Insure proper methods of fabrication 

 of the materials." 



The composition of the exhaust from liquid-fuel engines, R. W, Fenninq 

 {Jour. Inst. Mech. Engin. [London^, No. 4, (1916), II, pp. 185-236, figs. 9; Gas 

 Engine, 18 {1916), Nos. 5, pp. 242-258, figs. 6; 6, pp. 287-289, figs. 5).— With 

 reference to the practice of analyzing the exhaust gases of internal combustion 

 engines to determine the completeness of combustion and the probable strength 

 of the air fuel mixture supplied, a method of constructing exhaust gas charts 

 for suitable fuels without the use of an engine is described and the results 

 of numerous experiments relating thereto reported. The experiments consisted 

 of a comparison of the composition of the products of combustion of prepared 

 mixtures of air and vaporized fuel in known proportions exploded in a small 

 vessel with the composition of the exhaust gases from an internal-combustion 

 engine. 



From the results of these experiments it is concluded that " with volatile 

 fuels there is but little difference in the composition of the products of com- 

 bustion resulting from air-fuel mixtures in a small explosion vessel or in an 

 engine cylinder in spite of the conditions being so dissimilar. The agreement 

 between the CO2, O2, and CO values in engine and explosion vessel tests is so 

 close that an exhaust gas chart prepared from explosion vessel tests can be 

 used to estimate the strength of mixture supplied to an engine. A very small 

 quantity, if any, of unsaturated or saturated hydrocarbons is present in engine 

 exhaust gases. Taking a particular instance, methane is almost entirely absent. 

 The hydrogen constituent in exhausts from strong mixtures is an important 

 item and increases in value rapidly with increase in mixture strength. The 

 ratio of air to fuel in the original mixture can be calculated with a considerable 

 degree of accuracy from the composition of the exhaust gases." 



[Tractor specifications], P. S. Rose {Amer. Thresherman, 19 {1916), No. S, 

 pp. 1-4, 6, figs. 2). — A table of specifications for 144 tractors of 91 different 

 makes is given, together with two diagrams showing arrangements of tractor 

 wheels and styles of motors. 



[Drawbar pull of tractor], R. Olney {Power Farming, 25 {1916), No. 5, 

 pp. 7-9, figs. 2). — This article discusses the drawbar rating of tractors in terms 

 of horsepower and gives a set of curves and a table of data showing tractor 

 speed in miles per hour, drawbar pull in pounds, and drawbar horsepower 



pounds pull X speed in miles per hour 



based on the formula Horsepower= . 



375 



The construction of the dairy house, H. A. Rtjehe {Illinois Sta. Circ. 188 

 {1916), pp. 8, figs. 4). — The general principles to be followed in dairy house 

 construction and ecLuipmcnt are presented by discussion and diagrammatic 

 illustrations. 



