STRAINED MINERALS EASILY DISSOLVED. 97 



to assist the chemical reaction. That it is utilized is shown by the fact 

 that the heat of combination of the resultant chemical compound must 

 be the same whatever the condition of the metal. Hence less chemical 

 energy is required for the solution of a strained metal, and the reaction is 

 promoted by the state of the strain. 



The validity of this reasoning is dependent upon the principle of the 

 conservation of energy. As a result of my studies in the phenomena of 

 recrystallization," I became convinced that strained minerals are more 

 readily acted upon by underground solutions than unstrained minerals. 

 (See pp. 690-692.) Barus's experiments already cited suggested the above 

 explanation. I then predicted that experiments would show that strained 

 metals are more readily acted upon chemically than unstrained ones, and 

 asked that this prediction be tested experimentally. This Mr. Hambuechen 

 has done in reference to iron, with the following results : 



The application of stress to metals causes an increase in chemical activity, this 

 increase being especially marked after the elastic limit has been reached. 



It is possible to get a curve showing the relation of electro-motive force to 

 strain which is similar to that of stress to strain. 



There is a definite relation between the electrical potential of iron toward an 

 electrolyte and the amount of energy stored up in the metal through the application 

 of stress.* 



Thus complete experimental confirmation of this prediction is made so 

 far as iron is concerned; and it can hardly be doubted that this illustrates 

 the general principle above given. 



Applying the above principles to strain and chemical action, it may be 

 said that in so far as minerals are strained either within or beyond the 

 elastic limit, this potentializes energy and puts such minerals into a 

 condition more favorable for chemical reactions than unstrained minerals. 

 All rocks, except at the very surface of the earth, are under stress, and 

 therefore strained to some extent at all times. It is true that the amount 

 of stress may not be great within a few meters of the surface; but with 

 increase of depth the averag-e amount of stress becomes more important. 

 In most cases of ordinary horizontal rocks near the surface it is customary 



"Compare Van Hise, C. R., Metamorphism of rocks and rock flovvage: Bull. Geol. Soc. America, 

 vol. 9, 1898, p. 300. 



i Hambuechen, Carl, An experimental study of the corrosion of iron under different conditions: 

 Bull. Univ. of Wisconsin No. 42 (Engr. ser., vol. 2, No. 8), 1900, p. 255. 



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