174 R. Bunsen — Cahrimetric Investigations. 



fastened on a heavy iron stand by means of a vice, whose jaws 

 surround tightly the lower part of the iron head-piece d. 



The amount of heat which a body evolves in cooling from a 

 given temperature to 0° C, is determined by dropping it into 

 the water in the vessel a and thereupon closing the vessel at 6 

 with a cork, to prevent any circulation of air. If the problem 

 be the relative measurements of quantities of heat, as in tk 

 determination of specific heats, then the standard of comparison 

 is directly afforded by the number of scale-divisions wMcli 

 the mercury thread has passed on its retreat. If the readings 

 are rendered in an absolute measure, as for instance, in grams of 

 melted ice, or in units of heat, as the unit in the following pr""^ 

 (always that quantity of heat being understood which onegr; • 

 water at 0^ C. absorbs in order to raise its temperature to 1 

 then It is only necessary to multiply the readings on the ; 

 with a constant which results from the following consicleran 



A mercury thread measured in the scale tube, which has the 

 temperature f and occupies T divisions of the tube after being 

 corrected by the calibration table, weighs g grams. Let further 

 the specific gravity of mercury at 0° 0. be S,, its coefficient ot 

 expansion «, then is the volume v of a corrected division on tk 

 scale, measured in cubic centimeters, 



and therefore 



V =L 0-00007Y33 c.c. (1) 



If the specific gravity of ice at 0° C. be denoted by S„ the spe- 

 cific gravity of water at the same temperature by S,, the weiga 

 ot melted ice expressed in grams, which corresponds to tue 

 volume V, that is, to one scale division with^, then is 



With regard to the specific gravity of 

 vations The following comparison sh< 

 among themselves. For S, 



^omson found 0-920 ' Pittcker and ) 



^e have many ob?er- 

 how little they ar^ 



Dufour, 

 Dufour, 



