536 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Metallography, etc. 



Application of the Microscope to the Study of Metals.* — Micro- 

 scopic examination of metals is considered by W. Rosenhain as giving 

 information upon (1) chemical constitution, the mode of combination of 

 the elements present, and the relative arrangement of the constituents ; 

 (2) defects existing in the metal, and the causes of failure ; (8) the 

 intimate structure of the constituents and the behaviour of the crystals 

 when the metal is strained. The author develops his theory of the struc- 

 ture of eutectics. The tin-lead eutectic appears to consist of spherulitic 

 crystals of tin, between the dendritic arms of which the lead has been 

 forced to solidify. The structure of all other eutectics examined is con- 

 sistent with the view that the metal present in larger quantity forms a 

 crystalline network, while the other metal solidifies in the interstices of 

 this network. The forms assumed by laminated eutectics have a striking 

 resemblance to the forms assumed under certain circumstances by thin 

 films of liquids under the action of surface tension. 



The author elsewhere f indicates the value of microscopic investiga- 

 tion of the causes of breakage of engineering materials. The first step 

 should be the examination of the microstructure of the material close to 

 the actual fracture, and also at some distance away from the fracture. 

 The inclusion of microscopic examination in the regular tests carried out 

 on engineering materials is advocated. The use of the Microscope to 

 control the annealing of copper and its alloys is described. 



Resistance of Metals to Impact.^ — T. E. Stanton and L. Bairstow 

 have determined the relative resistance to shock of thirteen samples of 

 wrought iron and steel of different carbon content. The methods of 

 testing were — 1. Bending-impact tests on notched specimens : (a) by 

 one blow ; (b) by repeated blows. 2. Impact tests by direct tension of 

 plain specimens : (a) by one blow ; (b) by repeated blows. Various static 

 tests were made for comparison. The results obtained lead the authors 

 to conclude that for the detection of two important faults in materials — 

 brittleness and low elastic resistance — two distinct tests are necessary. 

 The bending test on a notched bar seems to be the most searching ; for 

 the detection of brittleness the one-blow method should be used, while 

 weakness in elastic resistance is revealed by the many-blow method. The 

 development of slip lines in polished specimens submitted to alternate 

 blows in tension and compression was found to be the same as under 

 gradually applied alternating stress. Neumann lines were found in 

 specimens broken by a very small number of blows. 



F. W. Harbord § throws doubt on the value of impact testing be- 

 cause of the considerable variation between duplicate tests found in a com- 

 prehensive series of tests, which were carried out on various steels, to 

 compare different methods of impact testing on notched bars. 



* Journ. R. Soc. Arts, lvii. (1909) pp. 349-58 (6 figs.). 

 + Nature, lxxx. (1909) pp. 250-2 (2 figs.). 

 X Proc. Inst. Mech. Eng., 1908, pt. 4, pp. 889-919 (22 figs.). 

 § Tom. cit., pp, 921-71 (12 figs.). 



