﻿210 Radioactivity of the Rods of the St. Gothard Tunnel. 



Taking the means of both series of experiments we find the 

 Finsteraar granite has a mean radium content of 6*7 x 10" 12 

 and the Gothard Massif 3*5 x 10 -12 for the radium, and 

 2-15 Xl0~ 5 and 1*16 x 10~ 5 for the thorium. There is, 

 therefore, about double as much of tl e radioactive substances 

 in the granite as in the schists of the St. Gothard Massif. 

 And this disparity is even greater in the new series of 

 experiments, both in the case of radium and thorium. 



It is interesting to compare the approximate heat equi- 

 valents of the radioactive bodies in the two important sections 

 of the tunnel. Assuming that 1 gram of radium in equilibrium 

 with all of its series involves 201'6 gram-degrees per hour, 

 and that the same amount of thorium, also in equilibrium, 

 involves 238 xlO -5 gram-degree per hour, we find the 

 general means give for the radium 1351 X 10 -12 calorie in 

 the Finsteraar granite, and for the thorium 512 Xl0~ 12 cal. 

 The more recent experiments afford 1210 x 10~ 12 cal. for 

 the radium. The total radioactive heat in this section of the 

 tunnel is, therefore, 1863 X 10~ 12 cal. per hour, or 1722 x 10~ 12 

 cal , according as we take the general mean or the recent 

 values of the radium content. These results are practically 

 the same. In the St. Gothard or central section the general 

 mean of the radium experiment gives 833 x 10~ 12 cal., and 

 the mean of the recent radium experiment gives 666 x 10~ 12 

 cal. The heat due to thorium is 276 x 10" 12 cal. The 

 total heat is, therefore, 1109 x 10' 12 or 942 x 10~ 12 calorie. 

 These figures, where derived from the general mean, are 

 based on a total of 87 rock samples taken at an average 

 distance apart of 168 metres. The earlier series of rocks was 

 selected so as to be representative of the more abundant rock 

 species; the latter series was taken at random. 



StapfPs gradient measurements give (as quoted above) 

 20*9 metres as the maximum in the granite and 46*6 in the 

 St. Gothard schists. Assuming the conductivities the same, 

 there is about double the amount of heat escaping from 

 the granite than from the schists. There is probably not 

 much difference in the conductivities. This point has been 

 investigated in the case of the Simplon rocks*. In the 

 Simplon the conductivity of the granite across stratification 

 was found to be 0*0054 and along stratification 00069. 

 The gneiss and schists across cleavage gave 0*0063 and 

 along cleavage 0*0084. StapfFs explanation of the thermal 

 state of the granite does not commend itself. The solidifi- 

 cation of the granite must date back to Miocene times or 



* See Mr. Fox's paper : Minutes, Proc. Inst. Civil Engineers, clxviii. 

 p. 53. 



