86 Chemical and Physical Notes 



calculated, taking 13*596 as the density of mercury and 2'6 as 

 that of glass, and they are given in lines g and i respectively. 

 When the specific heat of a body is spoken of without further 

 qualification, the water value of I grm. of the substance is 

 meant. When we are dealing with volumes, we require to 

 know the specific heat per unit volume, and that is the water 

 value of i c.c. of the substance. Now the density of a sub- 

 stance, when the metrical system is used, is the weight of i c.c., 

 therefore the weight of i c.c. of mercury is 1 3-596 grms. and 

 that of the same volume of glass is 2'6 grms. Multiplying 

 13-596 by 0-033, the specific heat of mercury, we obtain 

 0*4486, which is the water value of i c.c. mercury, or its 

 specific heat per unit volume. Multiplying 2'6 by 0-198, we 

 obtain o'5 148 as the specific heat per unit volume of glass. If 

 now we multiply the volume of mercury, g, by 0-4486 and the 

 volume of glass, z, by 0-5148, we obtain h and k, the water 

 values of the volumes of mercury and of glass respectively. 

 The sum of these, /, is the water value of the bulb as a whole. 

 If the values of /be compared with those of fin the first part 

 of the table, the agreement will be found to be very close. 

 With regard to the mercury, there is not room for much dis- 

 crepancy, because it is an elementary body, and it can be used 

 in the construction of thermometers only when it is in a state 

 of purity. It is otherwise with the glass. Neither Berthelot 

 nor the makers give its composition, its density, or its specific 

 heat. Although the composition of the glass is of great im- 

 portance, a knowledge of it is not necessary for thermometric 

 or calorimetric purposes ; on the other hand, a knowledge of 

 both the density and the specific heat of the glass is essential. 

 Yet it is very rarely furnished. The values used in the table 

 are commonly occurring ones; and the agreement in the water 

 values of the glass arrived at in the first and second parts of 

 the table, lines e and k, shows that they apply to the glass 

 used. Having obtained the total volume of the bulb, m, and 



its water value, /, we obtain at once = , the specific heat 



m 



per unit volume of the bulb considered as a whole, or in other 

 words it is the water value of i c.c. of bulb. The values of 



