GROWTH OF EXPERIMENTAL SCIENCE 183 



111 this connection the experimental work carried out by Spring^® 

 should be mentioned. Although certain of Spring's results have been 

 called in question by FriedeP*^ and Jannettaz,-^ the whole field has been 

 revicAved by Johnston and Adams/^ of the Geophysical Laboratory at 

 Washington, and the bearing of Spring's work clearly set forth. Spring 

 has demonstrated that under high pressure certain substances unite chem- 

 ically with the production of new compounds. Thus copper and sulphur 

 when compressed to 5,000 atmospheres unite to form a black crystalline 

 cupreous sulphide, while barium carbonate and sodium sulphate yield 

 under a pressure of 6,000 atmospheres barium sulphate and sodium car- 

 bonate. Johnston and Adams, however, have pointed out that a careful 

 distinction must be made between simple cubic or hydrostatic compres- 

 sion and differential pressure which gives rise to a shearing movement or 

 flow within the mass. The former produces but little effect in developing 

 chemical change ; the latter, however, does in many cases produce impor- 

 tant alterations in chemical composition and is in a way analogous to a 

 long-continued grinding together of the reacting substances in a mortar. 

 In some cases the apparent interchange may be due to a process of diffu- 

 sion occurring between the particles of the two substances brought into 

 intimate contact by the pressure to which they are submitted. We have, 

 by submitting a mixture of certain salts to such differential pressure, 

 giving rise to flow, obtained foliated structures with a development of 

 new compounds, which reproduce in a striking manner certain structures 

 seen in the crystalline schists of highly contorted portions of the earth's 

 crust. 



Another very important fact is that when minerals of an acicular 

 habit are developed in a rock which is undergoing deformation by differ- 

 ential pressure these new minerals grow in the mass with their longer 

 axes orientated at right angles to the direction in which the pressure is 

 being exerted, as shown by the experiments of F. E. Wright^^ on certain 

 glasses which were allowed to crystallize when flowing under differential 

 pressure, as well as by a series of experiments by the writer, the results 

 of which have not as yet appeared, in which gypsum is converted into a 

 lower hydrate while submitted to heavy differential pressure. In these 

 cases crystalline rocks result, showing distinct foliation, the plane of this 



^^ Recherches sur la Propriete que poss&dent les corps de se souder sous Taction do la 

 Pression. Revue Universelle des Mines (and many other papers). 



20 Bull. Soc. Chem. (2), vol. xxxix, 1883, p. 626. 



siJbid. (2), vol. xl, 188.3, p. .51. 



-2 On the effect of high pressures on the physical and chemical behavior of solids. 

 Am. Jour. Sci., March, 1913. 



23 Schistosity by crystallization — a qualitative proof. Am. .Tour. Sci.. Sept.. 1006. 



XIV— Bull. Geol. Soc. Am., Vol. 29, 1917 



