. [ 231 ] 

 XII. On the Expansion by Heat of Water and Mercury. By A. Matthiessen, F.R.S. 



Received December 7, — Road December 21, 1865. 



The fact pointed out in my report "On the Chemical Nature of Alloys"*, that their 

 physical properties may in this respect be divided into two classes, namely (1) those 

 which do not indicate their chemical nature, and (2) those which do indicate their 

 chemical nature, has led me to investigate the property of expansion by heat, so as to 

 find the law which regulates the expansion of alloys, as well as to determine to which 

 of the above classes this property belongs. 



To do this, it was first necessary to determine the coefficients of expansion of the 

 metals to be employed in making the alloys ; and in carrying out this research, it had 

 to be borne in mind that bars of a sufficient length to determine the linear coefficients 

 of expansion with accuracy would require very large quantities of the pure metals 

 to'make the alloys, in fact such quantities as it would be impracticable to prepare, A 

 method had therefore to be devised by which the expansion of small quantities of the 

 metals and their alloys could be determined, and at once one suggested itself, namely, 

 that of weighing the metal or alloy in water of different temperatures. This method 

 has been already employed for the determination of the coefficient of expansion of water 

 by Hallsteom and Hagen. 



To check the method (basing the calculations on Kopp's coefficients of expansion for 

 water), the expansion of mercury was determined. - The coefficient deduced did not, 

 however, agree with Regnault's, as was expected, but, on the contrary, differed con- 

 siderably ; showing either an error in the method employed, or that either Kopp's or 

 Regnault's coefficients are faulty. After carefully considering the method employed 

 and obtaining always the same results, it then became necessary to redetermine the 

 coefficients of expansion of water and mercury ; and these redeterminations fonn the 

 subject of this memoir, which will be divided into four parts : — 



1. On the determination of the coefficient of linear expansion by heat of certain glass 

 rods. 



2. On the method employed for the determination of the coefficients of cubical expan- 

 sion by heat of water and mercury. 



3. On the redetermination of the coefficients of expansion by heat of water. 



4. On the redetermination of the coefficient of expansion by heat of mercury. 



• British Association Report, 1864. 



