234 Johnston and Adams — High Pressures on the 



mote the formation of larger crystals in such a block is a 

 question upon which there is at present no direct evidence.* 



Similarly the blocks formed by compressing filings or grains 

 of metal are, in general, agglomerates*!* of the original grains 

 cemented together by layers of deformed or flowed metal 

 around the edges ; such blocks show considerable rigidity, by 

 reason of this cementing action, and are stronger in proportion 

 to the total deformation produced by the compression. This 

 is in agreement with the well-known fact that the strength of 

 metals increases when they are deformed in any way (as by 

 hammering, rolling, or drawing to wire) — a fact which is in 

 harmony with the ideas here enunciated regarding the phe- 

 nomena resulting from unequal pressure and consequent flow;): 

 in the interstitial spaces. 



We should, therefore, conclude that recrystallization will 

 occur only in those parts (usually a small fraction of the whole 

 amount of material) which have been subjected to compression 

 sufficient to produce melting; and hence that the actual 

 amount of recrystallization would be greater as the amount of 

 deformation is greater and would be little or nothing at all 

 when the compression is uniform — a conclusion which is in 

 thorough accord with experiment. It is to be noted that the 

 crystalline form which appears is that which forms under the 

 particular conditions of temperature and pressure which obtain, 

 and is not necessarily the form which w^ould appear under 

 normal circumstances. 



With regard to the transformation of plastic sulphur into 

 orthorhombic sulphur (the stable form under ordinary condi- 

 tions) Spring's statements may be quoted in full. 



" Prismatic sulphur. — Freshly prepared transparent prisma- 

 tic sulphur was subjected to a pressure of 5000 atm. at a 

 temperature of 13°. An opaque block, much harder than those 

 obtained by melting, resulted. Microscopic examination of the 

 fracture showed it to be identical with orthorhombic sulphur; 

 from which one might suspect that the transformation of the 

 prismatic into the orthorhombic form had occurred. In order 

 to assure myself of this, I have found that the melting point 

 of a fragment of the block formed by compression was 115° ; 

 now prismatic sulphur melts at 120°, orthorhombic sulphur 

 between 111° and 114°. Moreover, the density of the block 

 w r as 2*0156, whereas that of orthorhombic sulphur is 2 05 and 

 that of the prismatic form is 1*96. These facts are in agree- 

 ment as evidence of the transformation. 



*Cf. p. 248. 



+ Jannettaz, Bull. soc. claim., xl, 53, 1883; Hallock, U. S. Geol. Survey, 

 Bull. 55, 71, 1889; Spezia, Atti Accarl. Sci. Torino, xlv, 1-16, 1910. 



% This matter is treated on page 219, and at length in the paper already 

 referred to on p. 218. 



