398 GEOLOGY OF THE COMSTOCK LODE. 



by a laborious process of" gradual ap2:)roximation. As even in final experi- 

 ments the thermal effect may escape detection, the purpose of the first experi- 

 ments may be said to consist in reducing- the positive and negative limits 

 within whicli this effect must lie to the smallest possible interval. 



Character of the experiments. — lu proccsscs sucli as kaolinizatiou, actioH may 

 usually be accelerated b^^ an increase of temperature, provided that the latter 

 is not sufficient to render the products unstable in a normal case. In the 

 experiments it would have been desirable to act upon the rock with steam at a 

 temperature from the boiling point of water upward, but with the primitive 

 facilities available in Nevada, the use of superheated steam was not practi- 

 cable. 



The apparatus in which the rock was subjected to the action of steam 

 closely resembles that usually employed for the determination of the boiling 

 point of thermometers. The rock to be acted upon was crushed fine and 

 packed into a cylindrical receptacle open at the top, and provided with a 

 wire-gauze bottom. This was supported in the steam space of a boiler 

 provided with an external packing. The object of the arrangement was to 

 allow the heat, possibly generated in the mass of rock by the process of kao- 

 linizatiou, to accumulate. 



Measurements of temperature. — Tlic difference of teuiperature between the in- 

 terior of the rock and the steam surrounding it was determined by the 

 aid of a thermopile consisting of three bismuth-platinum couples, one junc- 

 tion being placed at tlie center of the pulverized rock, and the other in the 

 steam-jacket surrounding the rock receptacle. The electromotive force was 

 measured by a method of compensation. The constants of the apparatus 

 were frequently rechecked, and divers precautions were observed in the 

 experimentation, and in the mathematical ti'eatment of the measurements, 

 as is explained in Chapter IX. The means employed enabled the observer to 

 detect a variation in the difference of temperature between the two ends of 

 the thermopile as small as 0.001° C. 



Details of apparatus and method. — Tlic boiler was hcatcd by two kerosene stoves, 

 each containing two bi'oad wicks. The oil could be replenished without 

 interfering to an appreciable extent with the flames. The water lost by 

 evaporation was replaced drop by drop by means of a simple device, and a 



