RICIL\RDS AND MATHEWS. — HEAT OF EVAPORATION. 



521 



sation, resorted to superheating the 

 vapor, in order to insure its being 

 perfectly dry ; accordingly we, too, 

 tested this doubtful device. A coil 

 of fine platinum wire was introduced 

 into our vapor delivery tube, extend- 

 ing nearly its whole length, and a 

 small current was sent through the 

 wire. Several determinations made 

 at different speeds and Avith different 

 strengths of current through the coil, 

 gave higher values than before. With 

 a constant strength of current, the 

 slower the speed, the higher was the 

 result ; and with a constant rate of 

 evaporation, the greater the current 

 the higher was the result. Evidently 

 superheating occurred. With some 

 modifications of the parts and the 

 construction of special thermometers 

 it would have been possible to take 

 the temperature of the vapor as it 

 entered the calorimeter ; but the un- 

 satisfactory nature of these experi- 

 ments offered no temptation to the 

 further prosecution of this line of 

 attack. 



Being still convinced that the prin- 

 cipal premature condensation took 

 place in the narrow zone between the 

 vaporizer and the condenser, we next 

 sought to reduce further this distance, 

 and to protect the vapor passing 

 through it from loss of heat. A new 

 vaporizer having a vacuum jacket was 

 constructed as shown in Figure 3, the 

 walls (B) of the jacket being about 

 one centimeter from the walls (A) of 

 the vaporizer, save at the bottom 

 where the distance was about eight 

 millimeters. Both the outer wall of 

 the vaporizer and the inner wall of 



Figure 3. A Further Modifica- 

 tion of Kahlenberg's Vaporizer. 



The compartment containing the 

 Hquid and coiled phxtinum wire for 

 heating is surrounded by a silver(>d 

 vacuum jacket (AB). The trap (C) 

 is retained. The condenser is at- 

 tached at G. The vaporizer is 

 immersed in the water of the calor- 

 imeter as far as the water-line at F. 



