84 Chemical and Physical Notes 



0-4486 grm. of water. The density of ordinary glass may be 

 taken at 2*6 and its specific heat at 0-198, whence the capacity 

 for heat of I c.c. of glass is the same as that of 0*5148 grm. 

 of water. Therefore when referred to unit volume the specific 

 heats of these two bodies are very nearly identical, and if we 

 have the total volume and apply the mean of the above 

 values, the result will be a very close approximation to the 

 water value of the bulb, quite independently of the exact 

 proportion in which the mercury and the glass enter into its 

 construction. Suppose that the displacement of the bulb 

 were I c.c. and that the glass were infinitely thin, so that 

 the bulb were all mercury, then its water value would be 

 0*4486 grm. If, on the other hand, the internal volume of 

 the bulb were infinitely small, so that it consisted entirely of 

 glass, its water value would be 0*5148 grm. But the bulbs 

 of thermometers of most ordinary patterns are very much 

 alike in construction. It is not usual in the construction of 

 even the best instruments to take into account the amount 

 of mercury or of glass present in the bulb. Such data are 

 available only in the case of thermometers especially con- 

 structed for use in calorimeters. As they are themselves 

 parts of the calorimeter, their heat constants must be 

 ascertained ; and, as was pointed out above, this is most 

 easily and most accurately done during their construction. 

 Berthelot 1 gives the thermal constants of three thermometers 

 which were determined during construction. These are em- 

 bodied in columns I, 2 and 3 of the following table. Column 

 4 refers to a thermometer belonging to the writer ; it is by 

 Chabaud, of Paris, and is constructed for use with Berthelot's 

 calorimeter. The data were ascertained during construction, 

 and are engraved upon the stem. 



In the following table the numerical data in the first 

 part are taken from Berthelot's Mccanique chimique, pp. 162, 

 167. 



In this table the fundamental gravimetric data are b the 

 weight of mercury and d the weight of glass in the bulb 



1 Essai deMtcanique chimique, fondee sur la Thermochimie, par M. Berthelot, 

 Membre de 1'Institut, Paris. Dunod, 1879. 



