250 



Messrs. T. Andrews and C. R Andrews. [Apr. 23, 



" Microscopic Effects of Stress on Platinnni." By Thomas 

 .Andrews, F.B.S., F.C.S., and Charles Begixald Andeews. 

 Received April 23,— Bead May 15, 1902. 



[Plate 4.] 



The microscopic effects of stress on platinum do not appear to have 

 been studied. An ingot of pure platinum was therefore prepared, and 

 from this a portion was accurately machined in the form of a cube, 

 0'30 inch square, which was afterwards carefully microscopically 

 polished, and then subjected to compressive stress in the testing 

 machine. 



Prior to the application of stress, and for comparative purposes, a 

 polished face of the platinum cube was microscopically examined, but 

 an even polished surface only was observed. A force producing a 

 compression of 10 per cent, on the total height of the cube was then 

 applied, and microscopic observations were taken at high magninca- 

 tibns of the effects of the stress on the micro-crystalline structure of 

 the platinum cube. The particulars of the stress applied are given 

 on Table I. 



Table I. — Compressive Stress applied to Platinum Cube. 





Cross- 

 section. 

 Dimensions, 

 inches. 



Area. 

 Square 

 inches. 



Stress required to 

 Height i ^ i 

 , » & compress sample 



teT ! 10 per cent, of 

 j n its original height, 

 lncnes. j Toris per square incli. 



Platinum cube. . 



-30 x -29 



-087 



0-30 12-82 



! 



The polished side of the cube upon which the high-power micro- 

 scopic examination was made was the one in line, or in parallel, with 

 the direction of the compressive force. The results observed were 

 very interesting, and confirm Professor Ewing's and Mr. Bosenhain's 

 observations on the peculiar manner in which the crystalline structure 

 of a mass of metal becomes altered when under stress.* 



On comparing the appearance of the platinum after having been 

 stressed with its appearance before the application of stress, it was 

 found that many of the individual large or primary crystal grains 

 forming the mass had, under the influence of the strain, developed 

 innumerable fine " stress bands " or " slip bands," or indications of 

 crystalline slip. The main lines of disruption were noticed in many 

 instances to roughly approximate to an angle of about -45° to the 



* Baterian Lecture, 1899, ' Phil. Trans.,' A, vol. 193, 1900, p. 353. 



