'255 



cj'linder is closed by a cork at the top and one at the bottom and, 

 that it may be heated electrically, it is provided with a layer of isolated 

 wire. The whole stands on a little table under a glass, which only 

 allows of |)assage to the wires of the heating-current IT and those 

 of the thermocurrent 7'. 



The research consisted in the determination of the temperature- 

 time curve with a constant, heating current. If this heating current 

 is closed, the temperature first rises quickly, then more slowMy and 

 asymptotically approaches a limit value. If now (also before the 

 limit-temperature is reached) the heating current is weakened and 

 then kept constant, the temperature tirst falls rapidly, then more 

 slowly till a second lower limiting temperature is reached. 



Wtien within the temperature-region in observation the substance in 

 the beaker melts, congelates, or in general undergoes some change 

 of phase, this will be observable on the T-t curve. So during the 

 supply of heat to the beaker the melting will appear as a sharp 

 twist in the ascending branch. The place of the twist indicates the 

 melting-temperature and that with a much higher degree of accuracy, 

 than would even be possible with a measuring of the temperature 

 within the substance. 



The second contact place of the thermo-element was in melting 

 ice during the time of observation. The thermo-current was measured 

 by a quick-indicating galvanometer of Moll. To keep the deviations 

 within bounds the thermoforce was tirst for the greater part com- 

 pensated with the help of a constant current-source and a shunt, 

 and besides the sensitiveness of the galvanometer was strongly 

 reduced. 



The deviations of the galvanometer were registered and the T-t 

 curves thus photographed. The figures 2 — 6 are reduced repro- 

 ductions of our original photos. The figures put underneath give in 

 an arbitrary measure the temporal value of the heating-current. 



An abscisslength of 8 cm. corresponds to a quarter of an hour. 



The dotted line indicates the same temperature of about 118° in 

 the different figures. 



Discussion of the Results. 



Fig. 2. The two ascending branches fully agree and at A the 

 first point of transition shows itself sliarpl}*, i.e. the melting point 

 of the solid substance. This temperatnre, which amounts to about 118°, 

 we have always chosen as point of departure. The strong oscillations 



17* 



