ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 251 



pressure is different accordins: as the pressure is applied statically or 

 ballistically. The difference may amount to aljout 8 p.c. 



Relation between Breaking Stress and Extension in Tensile 

 Tests of Steel.* — In this paper "breaking stress" is used to mean 

 maximum tension per unit of area of original cross-section of test-}3iece, 

 and " intrinsic strength " to mean actual intensity of the stress at the 

 broken surface. It has been observed that for test pieces a few 

 diameters in length, the sum of breaking stress (in tons per square inch) 

 and elongation per cent, is very nearly a constant, equal to 67-68, for 

 mild steels free from internal mechanical strain. A. Mallock shoAvs 

 mathematically that this follows from the assumption that the intrinsic 

 strength of a material is a quantity which is not altered by heat treat- 

 ment. The intrinsic strength of all ordinary steels (excluding cold- 

 worked material) appears to be about 70 tons per square inch. 



The Art of Cutting Metals.f — A section of this technical engineering 

 paper by F. W. Taylor, is devoted to an elementary discussion of the 

 micro-constitution and theory of hardening of tool steels. The author 

 criticises Carpenter's explanation of the characteristic properties of high 

 speed steels, and expresses the opinion that no satisfactory explanation 

 of "red-hardness" — i.e. the quality of maintaining a cutting edge at a 

 red heat — has yet been advanced. 



Crystallography of Iron.| — Though it has been shown that the 

 three allotropic states of iron all crystallise in the cubic system, it 

 would appear probable that differences in their intimate structm-e exist. 

 F. Osmond and G. Cartaud here describe the experimental methods they 

 have adopted, and the results obtained in the further study of this 

 subject. Characters capable of yielding information are :— (1) deforma- 

 tion figures, including lines of translation and mechanical twinning ; 

 (2) congenital twinning ; (o) twinning resulting from annealing after 

 deformation ; (4) mechanical properties functional of the crystalline 

 orientation ; (.5) corrosion figures ; (6) synchronous crystallisation 

 figures : (7) segregation figures. For work on a and /3 iron, the speci- 

 mens used were very coarsely crystalline fragments of iron, from which 

 single crystals could be cut. At ordinary temperatures these were 

 a iron, at 800° C. jB iron. For y iron, samples of manganese steel and 

 nickel steel were used at ordinary temperatures, the size of the crystals 

 being as large as could be obtained. The authors found that the three 

 modifications exhibited important differences in crystalline characteristics, 

 and embody their results in a table. They suggest, as a possible inter- 

 pretation, that in the a state the mesh is a simple cube, while the mesh 

 of ^ iron is a centred cube, and that of y iron a cube with centred faces. 

 The authors, however, consider attempts at interpretation to be prema- 

 ture. 



Constitution of Iron-Carbon Alloys.§ — A. Sauveur discusses the 

 Roozeboom diagram. The eutectic forming at about 11;-)0°C., and 



* Proc. Roy. Soc, Series A, Ixxviii. (1907) pp. 472-8 ^5 figs.). 

 + Proc. Amer Soc. Mech. Eug., xxviii. (1906) pp. 1-248 (154 figs.). 

 : Journ. Iron and Steel Inst., Ixxi. (1906) pp. 444-92 (37 figs.). 

 § Op. cit., Ixxii. (1906) pp. 493-575 ( 12 figs.). 



