﻿] 74 Prof. R. Bunsen's Calorimetric Researches. 



The mean independent alteration of the mercury-thread in the 

 experiment amounted in a minute to 



2\m x m 1 /^ 

 and during the entire duration of the experiment, 



v l y/ 2 v?? mj 



divisions of the scale. This value is to be added as a correction 

 to the indication of the mercury- thread Q — Q t observed in the 

 experiment, and the negative sign used whenever, independent 

 of the experiment, a melting of ice was indicated ; in the oppo- 

 site case a positive sign must be used. 



For the indication T corresponding to the amount of heat 

 measured, we obtain therefore the equation 



. T=(Q -Q I ) + (M 1 -M )|g o + ^) ; . . (5) 



in which we need scarcely remark that the values of the table of 

 calibration are to be substituted for the direct readings to which 

 they correspond. 



2. Estimation of Specific Heat. 



In order to obtain the specific heat of a substance, it is best 

 to estimate once for all, in divisions of the scale, the amount of 

 heat given up by one gramme of water when it is cooled from 

 1° C. to 0° C. ; we have then to divide by this value, W^, the 

 amount of heat W which a grain of the substance to be examined 

 loses under the same circumstances. Suppose the weight of sub- 

 stance to be G, its temperature t y the number of corrected divi- 

 sions of the scale T, then we obtain the desired specific heat 

 from the equation 



S= TC (6) 



in which t represents the boiling-point of water at the barometric 

 pressure which existed during the experiment. 



The apparatus (fig. 4) is employed to impart to substances the 

 constant temperature t ; and it is represented one- sixth of its real 

 size. The tin-plate vessel A, provided with a water-gauge, holds 

 enough water to produce a current of steam for twelve hours 

 when heated by the gas-lamp underneath. The current of steam 

 passes through the india-rubber tube a and the outer glass ves- 

 sel (B) into the second india-rubber tube, b, which is connected 

 with an ordinary condenser. The heating- vessel (/) is placed 

 in the centre of B and is thus constantly surrounded with the 



