478 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The use of this method obviates at once the greatest source of error 

 in calorimetric work of all kinds, namely, the correction for cooling. 

 As the method may be employed in any kind of calorimetric work, 

 there seemed to be no reason why it should not be applicable to work 

 on specific heats ; and the present paper will show that it is indeed 

 of great service there. The application is extremely simple : the 

 substance to be studied should obviously be placed in a calorimeter 

 surrounded on all sides by a jacket, the temperature of which can be 

 changed to correspond exactly with the warming of the substance by 

 some known source of heat. 



It was first necessary to decide upon the exactly quantitative source 

 of energy to be used for heating the substance within the calorimeter. 

 Some experimenters have used merely the heat of a warmer body ; 

 others have used electrical heat ; and Thomsen availed himself of the 

 heat of combustion of hydrogen. Of course many other chemical 

 reactions might be employed for this purpose, as Ostwald and Luther 

 have pointed out ^o ; and after much consideration there was selected 

 for this present work the heat of neutralization of pure sulphuric acid 

 and sodic hydroxide as the most convenient, especially because it is 

 not very changeable with the temperature. 



Definite amounts of acid and alkali were allowed to react in a 

 platinum flask surrounded by the liquid in the calorimeter, and the 

 rise of temperature in the whole system was carefully noted. By 

 comparing the rise of temperature under these conditions with the 

 rise shown when pure water is in the calorimeter, a comparative 

 measurement of the heat capacity of the liquid is made. A few words 

 will suffice to explain the disposition of the apparatus and the method 

 of its use. 



Apparatus. 



A diagrammatic sketch of the apparatus in vortical section is seen in 

 Figure 1. First, the environment of the calorimeter will be described. 

 The jacket (A) was made of heavy sheet copper and was provided with 

 an outflow cock ( 10 for convenience in emptying. The soldered joints 

 were heavily coated with shellac to prevent corrosion by the alkaline 

 solution with which it was filled. The capacity was 17.5 liters. A 

 rotary, vaned stirrer (E), with a speed of 145 turns per minute, insured 

 thermal homogeneity in the contents of the jacket. To raise the 

 temperature, crude sulphuric acid was run into the jacket through 

 the funnel (F), into the alkali contained in the jacket, and the heat 

 of neutralization thus liberated was rapidly disseminated throughout 



20 Ostwald-Luther, Phys. chem. Messungen (1902), p. 204. 



