of some Rocks at Higli Temperatures. 



59 



thought that this central cooling might be due to vertical 

 circulation of air leaking through the asbestos, so in the 

 later determinations the furnace was laid horizontally, but 

 this did not cause any improvement. The only way of 

 eliminating this error is by the use of a longer or narrower 

 furnace and cylinder. However, by using comparatively 

 large values of W, and hence of A, the error becomes 

 negligible and consistent results are obtained. 



The results obtained for granite are shown in Table IV. 



Table IV. 



9. 



KxlO 3 . 



W. 



9. 



KxlO 3 . 



W. 



200 



473 



8-31 



[315 



4-55 



636] 



88 



5-04 



6-85 



[292 



5-32 



2-95] 



75 



517 



6-38 



345 

 450 



4-23 

 4-22 



13-72 

 2552 



385 

 203 



4-27 

 4-30 



1306 

 11-42 



537 



395 



25-19 



84 



4-61 



6-98 



443 



3-95 



10-51 



288 



4-25 



1535 









The results in brackets, which v\ere both obtained on the 

 same day, are disregarded, the values for K being too large 

 owing to the small values of W, and the high temperature 

 of the furnace as explained above. The other results are 

 plotted in fig. 5. As in the case of the limestone, progressive 

 lowering of the conductivity occurred though to a less 

 extent. 



The first three results lie on a curve somewhat similar to 

 those obtained with the limestone. 



The next six, beginning with that for a temperature of 385°, 

 lie along the curve 



K = (4-215 + 1'07 e-001187 0) x i -^ 

 or log (K - 0-004215) = 3-0296 - 0*005155 (9, 



the first member being slightly above the curve. 



The last two determinations at 537° 0. and 443° C. gave 

 the same result K = 3'95 x 10 -3 , indicating further lowering 

 of the conductivity when the r< ck was heated above 450°. 



