416 K T. Allen, F. K Wright and J. K. Clement - 



10 



New Method for Detecting the Direction of Sluggish Heat 

 Changes. — A substance in which a transformation progresses 

 so slowly that the accompanying heat change cannot be 

 detected by the ordinary method, should show it plainly if the 

 change could be forced to proceed with sufficient velocity. 

 The heat change would then be concentrated and become 

 visible on the temperature-time curve. 



In changes of this character, the rate of change depends on 

 the temperature, and increases rapidly with it. If, therefore, a 

 substance which is unstable at high temperatures be introduced 

 into a furnace which is several hundred degrees above the 

 lower limit of the unstable region, the heat effect is in general 

 easily followed. In our experiments the apparatus shown in 

 fig. 10 proved very satisfactory for the purpose. An empty 



platinum crucible is first placed 

 on a pedestal of refractory 

 material in the electric resist- 

 ance furnace. The unglazed 

 porcelain tube, A, l cm in inside 

 diameter and open at both 

 ends, passes through holes 

 drilled in the two covers, B 

 and B', and is then clamped 

 in the position shown in the 

 figure, the lower end of the 

 tube reaching down to the top 

 of the crucible. The thermo- 

 element C is covered by a 

 platinum shoe, D, which 

 should occupy the same posi- 

 tion in all the experiments, 

 i. e., about the center of the 

 charge. This is assured by 

 clamping the tube in a fixed 

 position and fastening the 

 element securely to it by plati- 

 num wire. Care was taken to 

 obtain like conditions in each 

 experiment, especial attention being given to fitting together 

 the parts of the furnace to obtain minimum radiation of heat, 

 and in placing the crucible and thermoelement in the same 

 relative position for each experiment. 



The furnace is now brought to a constant temperature, which 

 should be sufficiently high to insure a rapid change of state. 

 In the particular substances which we investigated, tempera- 

 tures ranging from 1425°-1475° were found best adapted to 

 show the heat effect. A weighed portion of the substance (40 



