﻿162 Prof. R. Bunsen's Calorimetric Researches. 



the outer vessel (b) from fi to \, with boiled water ; the remainder 

 of the vessel b up to the level 7 is filled with boiled mercury. 

 In order to arrange the instrument for use, a cylinder of ice 

 must be produced in the vessel b with which to surround the 

 vessel a completely. For this purpose the whole apparatus is 

 placed in a large vessel and surrounded with snow ; the cali- 

 brated scale-tube, s, fitted accurately into the cork with fine 

 sealing-wax, is then passed through the mercury in the collar (d), 

 and made fast in the mouth of the tube (c), so that it becomes 

 filled with mercury. That this may be accomplished without 

 risk to the somewhat fragile apparatus, the instrument is secured 

 in an iron support by means of a vice, which encloses firmly the 

 lower part of the iron collar (d) . 



The amount of heat which a body gives up by being cooled to 

 0° C. is estimated by dropping the body into the water con- 

 tained in the vessel a, which is then closed with a cork at 3 to 

 prevent change of air. If it behaves, on relative measurements 

 of amount of heat, in the same way as in the estimations of 

 specific heat, then this amount is obtained directly by observing 

 the number of degrees on the scale to which the thread of mer- 

 cury goes back. If the readings are to be converted into abso- 

 lute quantities (for example, into grammes of melted ice or 

 thermal units, viz. the amount of heat required to raise the tem- 

 perature of 1 grm. of water at 0° C. tol° C.),then the readings 

 from the scale have only to be multiplied by a constant, which 

 is derived from the following consideration: — 



A thread of mercury measured in the scale-tube, and at the 

 temperature t, and which assumes the temperature T after the 

 calibrating-corrections have been made, weighs g grms. Further, 

 let the specific weight of mercury at 0° C. be s q , and its coeffi- 

 cient of expansion a, then the volume v, measured in cub. cen- 

 tims., of a corrected scale is 



s q T 

 The instrument used by myself had the following : — 

 g =0-5326, 

 a =0-0001815, 



t =9° a, 



^ = 13-596, 



T=507'4; 

 and therefore 



v= 0-00007733 cub. centim (1) 



Let s e represent the specific gravity of ice at 0° C, s w the 



