RICHARDS AND LAMB. — SPECIFIC HEAT OF LIQUIDS. 6G3 



A New Method. 



Ill devising a new method for determining the specific heats of liquids, 

 the endeavor was made to retain the advantages of the method of Ilesehus, 

 while minimizing the disadvantages. The important objects to be accom- 

 plished were the following : — 



First, the thermometers must all be read while stationary, not with a 

 moving thread of mercury. 



Secondly, as little time as possible must be allowed for the cooling of 

 the hot liquid or the warming of the cold liquid. 



Tliirdly, conditions must be so adjusted that these two last-named 

 errors, each made as small as possible, should cancel one another. 



The first of these objects was attain'ed by keeping both the hot and 

 the cold liquids in very accurate thermostats before the moment of mix- 

 ing, and by mixing them in a calorimeter surrounded by a thermostat 

 maintained at the final temperature of the mixture. Thus all the tem- 

 peratures were measured accurately, without the possibility of thermo- 

 metric lag. 



The second object was attained by delivering the two liquids into the 

 mixing calorimeter simultaneously with great rapidity, having 23reviously 

 so adjusted their relative weights, and their relative temperatures, that 

 their equilibrium temperature would be nearly identical with that* in 

 the water jacket of the calorimeter. 



The third object was attained by making all the delivering apparatus 

 as similar as possible in the two cases, and by having the temperature 

 of the hot liquid as much above the final temperature as that of the cold 

 liquid was below it. 



The quickest adjustment of the final temperature is attained if the 

 liquids are allowed actually to mix, not merely to equalize their tem- 

 peratures through a heat-conducting septum. But if two liquids dis- 

 solve one another, they almost invariably evolve or absorb heat in the 

 process. This extra heat adds algebraically to the heat-capacity effect, 

 and must be subtracted in order to obtain this alone. Fortunately the 

 heat of reaction is easily found in the present case by making additional 

 experiments with the same apparatus, maintaining all the thermostats at 

 the same temperature ; or still more simply by means of another device 

 described on page G7o, 



With these data, knowing the specific heat of one of the liquids wdthin 

 the given range, it is easy to calculate both the specific heat of the other 

 liquid and that of the mixture, as will be shown. 



