484 EXPERIMENT STATION KECOED. [Vol.41 



reader with as nearly as possible a complete account of the development of the 

 art of water purification. Consideration is first given to the physical, chemical, 

 and biological properties and characteristics of various classes of water. The 

 relation of polluted public water supplies to water-borne diseases is given 

 special attention. The various eteps in purification processes such as plain 

 sedimentation, coagulation, filtration, and disinfection are described in con- 

 siderable detail. Special chapters are devoted to water softening and to the 

 removal of iron and manganese from ground water supplies. 



Water systems for farm homes, F. C. Fknton {Univ. Missouri, Agr. Ext. 

 Serv. Circ. 49 {1918), pp. 16, figs. 13). — ^This is a brief popular bulletin on the 

 subject, prepared with special reference to Missouri conditions. In addition 

 to the pneumatic system of water supply the so-called autopneumatic system, 

 the value of which has been much under discussion, is described as having been 

 in actual operation and having been found practical. It is stated, however, 

 that " many such systems have been in operation for years and are giving 

 excellent satisfaction, while others have given considerable trouble. Taking 

 everything into consideration, it can not be considered as reliable as some of 

 the other systems." 



The relation of the shrinkage and strength properties of wood to its specific 

 gravity, J. A., Newlin and T. R. C. Wilson {U. S. Dept. Agr. Bui. 676 {1919), 

 pp. 35, pis. 5, figs. 16). — This bulletin reports data on the relations of the 

 strength properties of woods to their specific gravity in such form as to render 

 them easily useful (1) for estimating the properties of any particular timber, 

 (2) for selecting timber for any given purpose, (3) for comparing the various 

 species, and (4) for determining to what uses different species are best adapted. 



Analyses of over 200,000 tests, made at the Forest Products Laboratory at 

 Madison, Wis., indicated a fairly constant relation between specific gravity and 

 strength. 



It was found in plotting the strength values in different tests to a natural scale 

 that in pi'actically every case a curve was formed corresponding to the general 

 equation f=p G **, in which f is the strength value, G the specific gravity, and 

 p and " are constants. Curves, equations, and data are given for shrinkage, 

 static bending, impact bending, compression, hardness, shearing, and tension 

 for both green and air-dry wood. 



The table on the opposite page gives equations for shrinkage and for each of 

 the strength properties of green and dry wood in terms of specific gravity. 



" In comparing different timbers or species, in estimating their various prop- 

 erties, and in finding species with exceptional strength in some properties 

 which may render them valuable for special xises, a knowledge of the specific 

 gravity strength relations is a valuable aid. . . . Such equations can never take 

 the place of tests of species whose properties are unknown. If any particular 

 mechanical property is known, the specific gravity may be approximated and 

 the other properties estimated ; even the properties of woods upon which no 

 test data are available can be estimated with a fair degree of accuracy from 

 the results of specific gravity determinations. Nevertheless, it is apparent from 

 a study of the table and diagrams that no one kind of test can replace a com- 

 plete series of tests." 



Wear-resisting values of various aggregates for concrete roads indicated, 

 H. S. Mattimore {Engin. Neics-Rec, 80> {1918), No. 18, pp. 861-863, figf;. 12).— 

 An impact testing machine designed to measure the re^sistance to impact of 

 different materials and mixes entering into the construction of concrete roads 

 is described and illustrated, and t^sts conducted by the New York State High- 

 way Commission on the impact resistance of several hundred different aggre- 

 gates and mixes are summarized. 



