232 Johnston and Adams — High Pressures on the 



tion. In the case of metals, this residual decrease of density 

 after compression is closely connected with the changes of 

 other properties produced by deformation, referred to else- 

 where in this paper. 



JB. The Alleged Effect of Compression in Producing Crystalline 

 Forms and hi Effecting Tra?isformatio7is. 



In the early paper previously referred to* Spring avers that 

 on subjecting certain substances to compression a recrystalli- 

 zation or a transformation from the amorphous to the crystal- 

 line state had occurred. The changes which Spring claims 

 to have effected in this manner are : the crystallization of 

 bismuth, zinc (at 130°), manganese dioxide, the sulphides of 

 zinc and lead, mercuric iodide, and the transformation of 

 plastic and monoclinic sulphur to the rhombohedral form. 



This conclusion was challenged by Friedel,t who failed to 

 observe any trace of crystallization on compressing to 10,000 

 atmospheres the sulphides of lead or zinc. Somewhat later 

 similar experiments were undertaken by E. Jannettaz;): on 

 a more extensive scale ; he too failed to confirm Spring's 

 deductions. Jannettaz states that in many substances pressure 

 develops not crystallization but schistosity, the plane of which 

 is perpendicular to the direction of pressure : this was demon- 

 strated by the difference in heat conductivity in the direction 

 normal to it. His conclusion is: "compressed powders do 

 not crystallize; a large number of substances — e. g. metals, 

 clays, graphite, steatite — under these conditions assume a 

 schistose structure, and exhibit the thermal properties charac- 

 teristic of this structure." 



Spring,§ in reply to this, points out that he had not claimed 

 that crystallization of a substance is a general consequence of 

 compressing it; out of 83 substances examined, there were 

 evidences of crystallization in only 7. In some of the cases he 

 had expressly stated that pressure has little or no effect, in this 

 respect agreeing entirely with the observations of Jannettaz. 

 He points out the necessity of working with clean substances 

 and in a vacuum, so that there may be no layer of foreign 

 material between the grains to be pressed together, and attrib- 

 utes to neglect of this precaution both the failure of Jannettaz 

 and Friedel to duplicate his results on crystallization and the 

 schistosity noted by Jannettaz. According to Spring, schistosity 

 is a secondary phenomenon, due to the interposition, between 



*Bull. Acad. Roy. Belg. (2), xlix. 323-79, 1880. 

 f Bull. soc. chiin. (2), xxxix, 626, 1883. 

 jlbid. (2), xl, 51, 1883. 

 §Ibid. (2), xl, 520-5, 1883. 



