Determination of the Heat- Capacity of a Thermometer. 49 



be determined. This latter volume, less the contained volume 

 of mercury, is the immersed volume of glass. 



The total immersed volume (V 3 ) of the thermometer is best 

 found from the weight (W) of the thermometer in air, and its 

 weight (Wi) when dipped in water to the same depth as it 

 dipped into the water of the calorimeter ; then 



V 3 =Wg rm --W 1 g rm - (2) 



But, if the bulb be cylindrical and of the same diameter as the 

 stem, this volume may be calculated from the measured length 

 and diameter of the immersed portion; for if of an irregular 

 shape it may be found by plunging it into a burette graduated 

 in cubic centimetres and partly filled with water ; but in both 

 cases with a less satisfactory result than is given by (2). 



The volume of the glass of the thermometer (V 2 ) immersed 

 in the water of the calorimeter is then 



v 2 =v 3 -Vi. 



These volumes of glass and mercury are converted into 

 their corresponding weights, using the mean specific gravities 

 of lead- and soda-glass already given. The sum of the pro- 

 ducts of the w r eight of the immersed glass and its specific 

 heat, and of the weight of the mercury and its specific heat, 

 is the required water-value of the part of the thermometer 

 dipping into the water in the calorimeter. 



Regnault has given the specific heat of thermometer-glass 

 as 0*2; but for greater accuracy it would be desirable that for 

 this value the mean specific heat of lead or of soda thermo- 

 meter-glass should be substituted according to circumstances *. 



The following is an illustration of the application of the 

 method : — 



Thermometer No. 2. Soda-glass. 



Weight of thermometer in air . . . = W 33*97 grm. 

 „ „ water . . 23*01 grm. 



Volume of thermometer . . . = V 10*96 c. c. 



Specific gravity of thermometer • . = S 3*098 

 Mean sp. gr. of soda-glass . . . . =S 2 2*512 

 Sp.gr. of Hg =Si 13*6 



Volume of mercury in thermometer = Vx=— ^ ~-^ 



=0*5795 c.c. bl ~" te2 



* It may perhaps be serviceable to call attention to the Physikalisch- 

 Chemische Tabellen of Landolt and Bornstein as a work which contains a 

 most useful collection of data. 



Phil. Mag. S. 5. Vol. 20. No. 122. July 1885. E 



