Subsurface Laboratory Methods 243 



and were placed in operation about January 1, 1947, and approximately 

 1,500 samples had been run by August 1, 1947. 



Figure 100 shows the apparatus as set up the mineralogical labora- 

 tory at Columbia University. For purposes of description, the apparatus 

 may be conveniently divided into four parts: the furnace, the sample 

 holder, the program controller, and the multirecorder. 



The furnace is a Hoskins 305 electrical-resistance furnace into which 

 an alundum tube (If inches inside diameter by 12 inches with a three- 

 sixteenths-inch wall) is inserted to diffuse the heat and to insulate the 

 metal specimen holder from the heater coils. The furnace is mounted 

 vertically on a track and can be raised or lowered over the specimen holder 

 by means of counterweights attached to two cables over pulleys. 



The specimen holder (fig. 101) is drilled from a cylindrical block of 



PLAN VIEW 



Figure 101. Nickel specimen holder. 



chrome-nickel steel If inches outside diameter and one inch in height. 

 Both pure nickel and chrome-nickel steel have been used, but the latter has 

 similar heat conductivity and is less subject to scaling. The six samples 

 to be tested are loaded in the outer holes numbered 1 to 6, while the 

 inner holes 1', 2', 3' are used for inert material, which is ordinarily puri- 

 fied alundum manufactured by the Norton Company. The dashed lines 

 indicate the connections between the two terminals of the chrome-alumel 

 differential thermocouples. Thus one hole containing alundum is suflB- 

 cient for the inert side of two differential couples. Chrome-alumel couples, 

 BXS22, were used for maximum electromotive-force generation and were 

 found to be substantial. The dots a indicate the position of the tempera- 

 ture-recording thermocouples. The terminals of these couples are adjusted 

 to the same height as the differential couples in the samples. The sample 

 and alundum holes are one-fourth inch in diameter and three-eighths inch 

 deep. 



The chrome-nickel-steel block is supported by an alundum tube (1| 



