﻿THE CRATER OF TAAL. 125 



It will be seen from the above that the sediment from water No. 3 

 is only very feebly radio-active, for it increases the natural air leak to 

 only five times the normal rate. It is not at all uncommon to encounter 

 clays and solids which increase it from fifty to one hundred times, in 

 fact Elster and Geitel 22 found a comparatively immense amount of 

 radium in the so-called "fango," a fine mud from hot springs in Battaglia, 

 northern Italy. Natural carbonic acid obtained at great depths from 

 old, volcanic soil was found to be radio-active by these observers. The 

 famous medicinal hot springs of Europe have all been examined, and 

 most of them have been found to be radio-active, but Curie and Laborde 

 and others have examined hot springs which are not radio-active, so that 

 the phenomenon is not entirely a general one. 



I do not attach too great importance to the actual numerical value 

 of the radium content of the sediment as it is calculated above, as the 

 apparatus used was somewhat crude, but the numbers given agree pretty 

 well with those obtained by others using a similar type of apparatus, but 

 certainly the amount of radium in this sediment is extremely small. In 

 fact Strutt, in examining various rocks, often found granites which gave 

 a higher value than the one found by me. Therefore, as so little radio- 

 activity was found in this one specimen, and especially as no trace of such 

 activitjr existed in the boiling, crater lake, it must be concluded that Taal 

 is a volcano which is not located over an area of a concentrated supply 

 of radium, and that therefore Dutton's theory will certainly not apply to 

 this volcano. 



Another fact which argues very strongly against Dutton's view is the 

 following: Radium is always associated with uranium or thorium. If 

 there were enough radium present in a limited area to melt the rocks, this 

 would also necessitate the presence of large amounts of uranium or 

 thorium. Volcanic lavas and ejecta have repeatedly been examined by 

 chemists, the analyses probably including thousands of specimens, and yet 

 no great quantity of uranium or thorium has been encountered in them. 

 If we calculate from the known radium content of pitchblende it be- 

 comes evident that if the heat given off by the minute amount of radium 

 which is present were to accumulate to a sufficient extent to melt the 

 rock, the latter would certainly need to be insulated in a much better 

 manner than we have ever been able to obtain in practice, or indeed 

 better than we have any reason to believe is possible within the earth's 

 crust. Furthermore, there is no evidence that would lead us to believe 

 that the radium content of any area could ever rise above that associated 

 with a pure uranium mineral, that is a quantity which for each gram 

 of uranium would represent 8X10" 7 gram of radium. The amount of 

 radium occuring in a mineral, per ton of uranium, is 0.72 gram, and it 

 has never been found to be more than this, it being probable that an 



22 Physikal Ztschr. (1903) 5, 11. 



