Heat of Granite and Basalt at High Temperatures. 60 



4P = Four times the thermo-electric power corresponding to t) 



read from another curve. 

 a = Bate of rise of temperature in degrees per minute. 

 W = Mean W- 0*712 a. 



E 3 = E.M.F. of the multiple couple in microvolts. 

 Z = Open circuit reading of the galvanometer. 

 X = Reading of the galvanometer with the couple cut out and 



potentiometer set to 10 microvolts. 

 Y = Reading of the galvanometer with the couple cut out and 



potentiometer set to 110 microvolts. 



Table II. (Granite) 



w. 



E 



Z. 



X. 



Y. 



e. 



E 4 . 



A. 



K. 



K'. 



7-985 



577 



278-5 



287-3 



364-8 



-1-5 



578-5 



9-40 



414 



415 



571 



264-5 



2763 



371-5 



-2-5 



5765 



9 37 



415 





629 



223-8 



236-7 



331-0 



-3-5 



632-5 



9-95 







; 7-746 



621 

 621-5 



224-8 

 224-3 



236-8 

 237-0 



329-8 

 331-0 



-3 

 -3-5 



624 

 625 



9v, 

 9-835 



3-S.O 



3-84 



3-845 



Mean Results for the day :— K=4'15 X 10-3 a t 237° C. 

 Iv=3-845xl0-3 a t395°C. 



Potentiometer error = 10 — 100 x 



X-Z 



This could not be 



single set of readings 



Y-X 



obtained directly as the potentiometer could not be set to 

 less than about 5 microvolts. 

 = E-* 



" 4P* 



= Conductivity calculated from 



neglecting a. 

 = Conductivity calculated from W and mean value of A for 



two consecutive sets of readings. 



It will be noticed that on this day on which two deter- 

 minations were made, the correction for a was quite negli- 

 gible and that for e was smaller than other probable errors. 



In attempting to obtain a determination at about 550° C 

 the single couple broke. This must have been caused by 

 thermal expansion of the rock as the couple joined again at 

 temperatures below 400° C. The determinations were 



