ZOOLOGY AND I'.OTANY, MICROSCOPY, ETC. 675 



test. It is suggested that mean pressure per unit area be taken to re- 

 present the hardness of the material tested, when the diameter of im- 

 pression is one-half the diameter of ball. Meyer's formula for expressing 

 the relation between load and diameter of impression, I* iiil n , is con- 

 tinned: the value of n almost invariably lies between 2 and 2 "5. The 

 author points out that ri— 2 may be taken to represent capacity for 

 hardening by cold work. 



T. Turner* discusses the definition of hardness, and compares, as 

 four typical methods for determining that property, the Turner sclero- 

 meter, the Shore scleroscope, the Briuell test, and the Keep drill test. 



Internal Friction in Loaded Materials.! — 0. II. Gulliver draws 

 the following conclusions from experimental work on the modes 

 of deformation of steel and other metals under stress, and from 

 theoretical considerations. The general directions of internal sliding 

 in a body under load, as revealed by the lines of Liiders and by 

 fractured surfaces, are consistent with the action of a frictional resist- 

 ance between the particles of the body, differing little from that of 

 ordinary external frictional resistance. Determinations of strength show 

 variations far too great to allow of even an approximate calculation of 

 the value of the coefficient of internal friction. 



Influence of Time and Temperature on Impact Tests. % — 

 A. le Ohatelier points out that rate of loading, in tensile tests at 

 temperatures above 100° C, has an enormous influence on the results. 

 Thus a mild steel wire, at 17<> C, gave a tensile strength of 45 kg. 

 per sq. mm., and elongation 10 p.c. when the test occupied 20 minutes, 

 while when the wire was broken in 2 seconds the tensile strength was 

 27 kg. and elongation 28 p.c. * It is probable that variations in speed 

 in shock tests will have an equally great influence. This being so, the 

 results given by Ghiillet and Revillon § will hold only for the speed of 

 testing used : probably at lower speeds the temperature of maximum 

 brittleness would be lower. The author summarises the results of his 

 experimental investigations on the effect of time and temperature on 

 the mechanical properties of steel. 



L. (luillet and L. Revillon || have made shock tests at temperatures 

 from 20-650° C. on a 0'35 p.c. carbon steel, causing the striking 

 velocity to vary through a considerable range. No effect due to varia- 

 tion in speed of testing could be detected, the temperature of maximum 

 brittleness remaining constant at 460-480° C. Further results of 

 shock tests at various temperatures are given for a number of special 

 steels, selected as possessing typical microscopic structures (pearlitic, 

 maitensitic, polyhedric, etc.). 



"Damping" in the Testing of Iron. 1— A. G-uillet suggests a new 

 method of testing metals. A metallic rod, fixed at one end, deformed 



* Journ. Iron and Steel lust., lxxix.(1909) pp. 426-43 (1 fig.). 



+ t'roc. Int. Assoc, for Testing Materials, No. 7 (1909) 7 pp. 



t Rev. de Metallurgie, vi. (1909) pp. 914-17. . 



§ See this Journal, 1909, p. 263. || Tom. cit., pp. 918-24 (2 tigs.). 



•J Rev. de Metallurgie, vi. (1909) pp. 8S5-7. 



