518 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



practice about six years ago at Harvard, has 

 since been used successfully in several calor- 

 imetric processes, such as the determination 

 of specific heats, heats of neutralization, com- 

 bustion, and solution. The method consists 

 in warming the surroundings of the calorim- 

 eter at the same rate and to the same extent 

 as the calorimeter itself during its operation. 

 This is accomplished by surrounding the 

 calorimeter proper by a watertight jacket, 

 which is immersed in a larger vessel contain- 

 ing dilute alkali. Into the latter can be 

 delivered the requisite amount of acid, the 

 bath being stirred rapidly so as to insure 

 uniformity of temperature. By such a sys- 

 tem it is possible to prevent heat-exchange 

 to or from the calorimeter proper, and the 

 thermometer is stationary during both the 

 initial and the final readings. 



For the measurements of the heat of vap- 

 orization a modified form of Kahlenberg's 

 apparatus was combined with the adiabatic 

 method of calorimetry. The exact form of 

 apparatus finally used was reached only by 

 degrees, several successive improvements 

 having been introduced. The first modifi- 

 cation of Kahlenberg's vaporizer consisted in 

 the interposition of a trap or hood (C in 

 Figures 1, 3, 4 and 5) between the boiling 

 liquid and the condenser, to prevent drops 

 of unvaporized material from being carried 

 into the latter by the lively current of vapor. 

 The objection to such a trap as that used 

 by Schiff (namely, premature condensation 

 Figure 1. First Modifi- of vapor) was avoided by keeping the trap 

 cation of Kahlenberg's Vap- entirely enclosed by the vapor of the boiling 



liquid, and therefore at the same temperature. 

 Furthermore it was made in such a form 

 as to prevent any danger of its filling and 

 running over. 



With this apparatus a number of prelim- 

 inary determinations were made, with a condenser and calorimeter to 



orizer. 



The hood or trap (C) over 

 the delivery tube helps to 

 eliminate mechanically car- 

 ried drops. 



