884 EXPERIMENT STATION RECORD. [Vol.41 



gineering are discussed, aud these are treated from a drainage standpoint. 

 . . . Some additional matter of a more strictly drainage engineering nature 

 has been included so as to make a more complete presentation of the principles 

 governing the design of underdrainage systems." 



Recommendations for farm drainage, W. J. Schlick {Iowa Engin. Expt. 

 Sta. Bui. 51 (1918), pp. 24, figs. 2). — This bulletin is prepared for the general 

 guidance of landowners and young drainage engineers, aud is intended to 

 give a good general knowledge of the main features of tlie farm drainage 

 system. 



Limestone rock asphalt produces good mortar, J. R. Nash {Engin. News- 

 Rec, 82 {1919), No. 19, p. 903).— Tests made at the University of Texas on mor- 

 tar made from a natural limestone rock asphalt showed the mortar to be 

 strong, light, and impermeable to Avater under 60 lbs. pressure for 48 liours. 

 The aggregate contained approximately 10 per cent of asphalt, the remaining 

 90 per cent being a comparatively soft limestone. Tests of the same aggregate 

 in concrete were not so satisfactory. 



Saturation of concrete reduces strength and elasticity, M. B. Lagaard 

 {Engin. News-Rec, 81 {1918), lYo. 20, pp. 908-910, figs. 6).— Tests conducted at 

 the University of Minnesota are reported using 1:2:4 trap rock concrete speci- 

 mens, in which it was found that moisture present in concrete as a distinctly 

 foreign element reduced its strength and modulus of elasticity, the effect being 

 greater on the strength. The i-eduction in strength due to saturation by water 

 which has been present in concrete from the time of casting was found in 

 some cases to be more than sufficient to overcome the increase in strength due 

 to better curing. It is concluded that the effect of saturation must be 

 recognized in an analysis of test data, aud the possibility of the resultant 

 weakening of the concrete must be considered in design. 



Compressing concrete increases its strength, F. P. McKibben {Engin. 

 N&ivs-Rec, 81 {1918), No. 23, pp. 1031-1033, figs. ^).— Tests conducted at Lehigh 

 University on the comparative compressive strengths of concrete columns of 

 1:2:4 concrete, in which half the number of specimens were compressed during 

 molding under loads varying from 160 to 260 lbs. per square inch, are reported. 



It was found that the compressed concrete weighed about 4 per cent more 

 per cubic foot than the uncompressed concrete. For specimens 28 days old, 

 the average compressive strength of the compressed concrete was 51 per cent 

 greater than that of the uncompressed concrete. The increase in strength due 

 to compressing increased considerably as the age of the specimen increased. 

 The stress deformation curves for the compressed concrete specimens were 

 much more nearly straight than the corresponding curves for the ordinary 

 concrete specimens. The ultimate compressive strength for the compressed 

 concrete 28 days old was 2,680 lbs. per square inch. The compressive strength 

 increased as the molding compression increased. It is concluded that the 

 strength of concrete can be materially increased by successive compression of 

 layers. 



Strength requirements for manilla rope (Engin. Neivs-Rcc, 82 (1919), No. 

 20, pp. 958, 959). — Data showing the weight and strength of three-strand manilla 

 rope, medium laid, as established by recent tests at the Bureau of Standards 

 are reported, and are sununarized in tlie following table: 



