50 Determination of the Heat- Capacity of a Thermometer. 



Weight of thermometer in air 33*97 grm. 



Weight of thermometer with lower end im-"} 

 mersed in water to the same depth as it > 29*73 

 was immersed in water of calorimeter ) 



Loss of weight = volume of immersed parti , ^j. 



of thermometer J 



Subtract contained volume of Hg=V! . =0*5797 



to get immersed volume of thermometer-glass =3*661 c.c. 



Weight of this volume of thermometer- glass ") Q ... Qr 



3*661x2*512 = | y iyo grm. 



Weight of contained Hg 6*5795 x 13*6 . =7*881 



Water-value of immersed glass 9*324 x 0*2 =1*840 

 Water- value of immersed Hg 7*881 x 0*0335 = 0*2639 



Total water-value of the immersed part of \9.-1nQQ 

 the thermometer J 



To test the reliability of the method, I sacrificed the ther- 

 mometer by cutting off the stem at the level at which it was 

 immersed in the water of the calorimeter, and weighed the 

 quantities of glass and mercury: there were9*63and7*64grms. 

 respectively, corresponding to a water-value of 2*182, which 

 ascribes to the above method an error of 3*7 per cent, in the 

 required correction. This negligible error is due to the volume 

 of the thermometer — consisting, not only of glass and mercury, 

 but also of the unfilled bore of the tube — and to slight deviation 

 of the specific gravity of the thermometer-glass from the mean 

 specific gravity used in the calculation. It may be just worth 

 pointing out that when a fragment of the thermometer-tube 

 is obtained from the maker with the instrument, these errors 

 may be avoided and the true water-value obtained. Probably 

 a greater error than the above is introduced into ordinary 

 specific-heat determinations by the evaporation of the water 

 in the calorimeter. 



II. A second method for the determination of the water- 

 value of the immersed part of a thermometer may be employed, 

 but it requires that the diameter of the bore of the stem be 

 known. To determine this a fragment of the same thermo- 

 meter-lube may be obtained from the maker of the instrument, 

 or a short piece of the upper part of the thermometer may be 

 very easily drawn-off before the blowpipe-flame, the closed 

 end of the fragment cut off, and the diameter of the bore 

 measured with a microscope furnished with a micrometer 



