64 



Scientific Proceedings, Royal Dublin Society. 



General Priiwipk of the Method. 



The apparatus consisting of a bulb at the end of a capillary tube (see 

 fig. 1) is filled at first with mercury ; and the expansion of the mercury in 

 the glass is determined by observations on the movement of the meniscus 

 along the stem as the temperature is altered through the required range. 

 The greater part of the mercury in the bulb is then removed and replaced 

 by the substance to be examined ; and the expansion of the substance and 

 the remaining portion of the mercury in the glass is again determined 

 by the movement of the meniscus through a range of temperature from a 

 little below to a little above the fusion-point. The conditions of temperature 

 and stem-exposure being the same in both cases, it is easy to obtain from the 

 tviTO sets of observations, and vs^ith certain weighings, the volume of the 

 known mass of substance at any temperature for which observations were 

 made. Tlie reduction of the observations resolves itself into finding at any 

 particular temperature w/wi mass of mercury in the bulb would at this known 

 temperature have the same volmnc as that occupied by the substance. If 

 this mass be divided by the known density of mercury at this temperature, 

 the volume of the substance is obtained. No corrections need be applied for 

 the expansion of the glass envelope, nor for expansion of the stem of tlie 

 dilatometer. 



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Fio. 1. 



Particulars of the Apparatus and Method. 



Apparatus. — The bulb, which may be of a flat or cylindrical form, is 

 connected to the capillary tube, which is bent in the form shown in fig. 1. 



