1902.] 



Microscopic Effects of Stress on Platinum. 



251 



line of the compressive force on the crystal sectional facets. Between 

 these larger indications of crystalline slip were observed a number of 

 extremely fine lines, indicative of the nature of the crystalline slip ; 

 many of these ran more or less in parallel lines in each individual 

 primary crystal or crystal grain, the direction of the orientation (or 

 line of the normal cleavage) of each primary crystal grain apparently 

 influencing the direction of the " slip bands," as seen in section. 



Owing to the varied orientation of the different crystals in the mass 

 of the platinum,* the lines of cleavage as indicated by the minute 

 "slip bands," were often seen at varied angles to the line of the 

 straining force. 



These experiments have also confirmed the observations of Pro- 

 fessor Ewing and others, that stress alone, without etching, sometimes 

 renders manifest the lines of intercrystalline junction of the large or 

 primary crystal grains of a stressed metal, providing that the stress is 

 of sufficient intensity. This will be seen on reference to the accom- 

 panying illustrations, Plate 4. 



The general appearance of the disintegration of the large or primary 

 crystal grains, produced by the pressure, on the pure platinum cube, 

 was the apparent breaking up of the crystalline structure of the 

 metallic mass, as seen in section, roughly diagonally to the line of the 

 compressive force. The area enclosed by the main lines of disruption 

 roughly approximating to the size of the large primary crystal grains. 

 The distances between the extremely fine lines, or " slip bands," ap- 

 peared roughly to coincide proportionately with the size of the 

 secondary or most minute crystals forming the mass, the finer "slip 

 bands " appearing to indicate the crystalline slip which had taken 

 place along the facets of the smaller or secondary crystals. The direc- 

 tion, however, of the main lines of the crystalline disruption did not 

 appear always to coincide with the intercrystalline facet junctions of 

 the large or primary crystal grains. The lines of least resistance, or 

 greatest crystalline slip, seemed chiefly to develop at an approximate 

 angle of about 45 degrees to the pressure line, as previously men- 

 tioned ; but the line of greatest weakness in the mass structure of 

 the metal was not always at that angle with the line of the disruptive 

 force. 



The previous description generally and approximately indicates the 

 effect observed, but the breaking up of the crystalline structure of the 

 metal appeared to be subject to modifications according to varied 

 internal or external conditions. 



* See " Micro-crystalline Structure of Platinum," by Thomas Andrews, ' Roy. 

 Soc. Proc.,' vol. 69, March 21, 1902, No. 457, p. 433; also "Microscopic 

 Structure of Gold and Grold Alloys," by Thomas Andrews, ' Engineering,' Septem- 

 ber 30, October 28, "December 9, 1898; also " Micro-metallograpby of Iron," by 

 Thomas Andrews, ' Eoy. Soc. Proc.,' toI. 58, 1895. 



