THE LINEAR COMPRESSIBILITY OF COPPER AND IRON, AND THE 

 CUBIC COMPRESSIBILITY OF MERCURY. 



INTRODUCTION. 



The recent determinations of the compressibilities of the elements all 

 depend upon that of mercury. A change in the accepted value of this 

 constant would affect all the others. It is true that their order of suc- 

 cession and their order of magnitude could not be changed, and that the 

 preceding conclusions concerning them could not be affected, by any prob- 

 able deviation of the accepted value of mercury from the true one ; never- 

 theless, before publishing so extensive an array of new data, it was thought 

 worth while to obtain further experimental evidence concerning the very 

 important fundamental value in question. 



The new method of Richards and Stull was used for the determination 

 of the compressibility of mercury in the following manner: The respec- 

 tive differences between the compressibilities of iron and mercury, and of 

 copper and mercury were determined; and then, by adding these differ- 

 ences to the absolute cubic compressibilities of these metals as found from 

 their linear measurement under compression, the absolute cubic compressi- 

 bility of mercury was found. 



The first part of this program was carried out by compressing the solid 

 metals in question under water and mercury, in a glass jacket exactly like 

 that used for the similar work with the alkali metals and the non-metals ; 

 and both experiment and calculation were wholly analogous to the pro- 

 cedures there described. Because the mercury could not be allowed to 

 come into contact with the copper for fear of amalgamation, more water 

 was needed to surround the solid in this case than in the case of iron. 

 Even in the latter case, however, the presence of some water was found 

 highly desirable to fill any small crevices or inequalities from which mer- 

 cury was excluded because of its high surface tension. 



The solid metals used were the purest commercial copper and wrought 

 iron, hammered and carefully turned to fit the jacket. In the case of iron 

 powerful hammering was especially necessary; in preliminary rejected 

 determinations indication was had of the existence of fine pores in the 

 metal. The samples used finally gave wholly satisfactory results. The 

 mercury was carefully purified by recognized means. 



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