STUDIES IN HYDROTHERMAL ALTERATION 



187 



at Pt, and the temperature rises. To adjust the oven for operation 

 at higher or lower temperatures the screw C, Fig. 6, is turned in and 

 the oven allowed to come to constant temperature. This requires 

 about one hour. If the temperature so obtained is too low, the 

 screw must be turned in still farther and such adjustments con- 

 tinued until the desired point is reached. Since the sensitiveness 

 of the oven is much greater with both contacts acting together, and 

 the expansion of the metals produces some torsion, it is necessary 

 to adjust the screws at K and K', until both coils Nos. 3 and 5 



Vr *^ \u 



suen 



A 



3* A 



p IG 4 _ — Under side of oven, showing wiring and arrangement of coils 



come on or off together. Parts of the regulator not otherwise 

 described are made of brass. 1 



This oven has proved highly satisfactory when used on an ordi- 

 nary 1 10-volt power or lighting circuit. At the highest temperature 

 at which it has been used, 300 C, the variations during several 

 weeks have not been more than 3 . It has been in use as long as 

 three months continuously, with similar slight variation, at about 

 180 C. Greater sensitiveness can be obtained by lengthening the 

 strip S. The device has also served as an efficient drying oven. 

 When but one of the six coils is being used— preferably No. 4, 

 because it is centrally placed— it maintains a temperature averaging 

 around no° C, without having the regulator in the circuit. 



1 The writer is indebted to Captain A. De Khotinsky of Kent Chemical Labo- 

 ratory for the greater part of the work in the design and construction of the oven. 



