STUDIES IN HYDROTHERMAL ALTERATION 



185 



The heating arrangement consists of six coils of No. 22 nichrome 

 wire wound on asbestos boards ^ inch thick, 1 inch high, and 7 inches 

 long. Each coil has a carrying capacity of three amperes and is 

 securely fastened to the bottom in order that the box may be used 

 in any position. Three of these coils are connected to a three-way 

 snap switch A, and three with a similar switch A', Fig. 4. By 

 this means from three to eighteen amperes may be in use at one 



Fig. 1. — A view of the oven 



time. The return wire is L, Fig. 4, which is also grounded on the 

 box. The connections of coils Nos. 3 and 5, Fig. 4, pass to the 

 thermo-regulator, T, Fig. 2, at R and R', thence through the screws 

 K and K' , Fig. 5, to the platinum contacts Pt, through the strip S 

 to the box and out via the lead wire L to B, the socket, Fig. 4. 



The construction of the thermo-regulator is as follows. A 

 strip S, consisting of an above piece of copper 0.022 inch thick, is 

 brazed to a piece of steel of the same thickness, and split longitu- 

 dinally for an inch back from the free end so as to produce two con- 

 tacts. S, Fig. 6, is fastened to the under side of block B, Fig. 5, 

 which is pivoted between E and E' . The latter are inset along the 



