878 DK. A. MATTHIESSEN ON THE EXPANSION 



internal cavities owing to the surface being rapidly cooled, and for this reason I have 

 not given the absolute weights of the metals or the alloys. 



It is worth remarking that the observed specific gravity of the alloy Bi Pbg difiers 

 considerably from the calculated one. . 



From the conclusions just drawn it would appear that the determinations oi the 

 expansion by heat of alloys give in general no indication as to their chemical nature, 

 and that this property belongs to that class of physical properties which does not indicate 

 their chemical nature. In the Report on the Chemical Nature of Alloys*, I have shown 

 that, from the detenninations of the electric conducting-power of alloys, we may gain an 

 insight into their chemical nature ; and basing my calculations on the hypothesis there 

 propounded, I am at present able to deduce the conducting-power of any alloy which 

 may be considered as a solidified solution of the one metal in the other, although it may 

 differ widely from that calculated from the mean conducting-power of the component 

 metals, as shown in Table XII. 



It is proper to point out that the coefficients given in Tables IV., V., VIII., and IX., 

 are those calculated from readings of the ordinary mercury-thermometer, the mercury 

 being contained in a tube of glass. Therefore, except at the two values 0° and 100°, the 

 temperatures indicated by the degrees of the thermometer I used will differ — 



I. From the temperature corresponding to the same number of degrees of an air- 

 thermometer. 



II. From the temperature corresponding to the same number of degrees of a mercu- 

 rial thermometer, the mercury being contained in a tube of some substance absolutely 

 unaffected as to its volume by heat, could such be found. 



The proper corrections can be deduced from the following Table : — 



This Table is copied from Recknagel. 



Regnault found 50° air-thermometer to correspond to 50°-20 by mercurial thermo- 

 meter. 



Professor Miller has sent me the following investigation of the correction to be applied 



* British Association Report, 1863. 



