Radioactivity of Terrestrial Surface Materials. 695 



grams are weighed out and mixed with the alkaline carbonates 

 or other fluxes required. The mixture is put directly into the 

 furnace. The platinum boat and all parts o£ the furnace 

 may be completely de-emanated by a preliminary heating, if 

 thought requisite. When experiments are being made daily 

 this naturally comes about. All the risky chemical opera- 

 tions of the method by solution — often involving a succession 

 of filtrations and fusions — are here avoided. 



But the most important advantage which can be claimed 

 for the method by fusion has still to be mentioned. The 

 method by solution is exposed to a source of error in the 

 liability of the radium present to assume the non-emanating 

 form — by adsorption or precipitation or from some other 

 cause. This is now fully recognized. It may be sometimes 

 detected in the erratic nature of results obtained in successive 

 experiments upon the one solution. Sometimes it appears 

 as if the presence of sulphates or gelatinous silica was re- 

 quisite. It is matter of satisfaction that Messrs. Eve and 

 Mcintosh, who first drew attention to this in the present 

 connexion, are now investigating the subject*. It does not 

 appear probable that any risk of this kind can beset the 

 method by fusion. 



The second point to which I referred above — the fact that 

 there is a substantial difference in the results of experimenis 

 made by solution and by fusion — will be illustrated in the 

 data contained in this paper. A study of the published 

 results obtained by solution shows much divergency. It 

 seems certain that this largely arises in the actual nature of 

 the material. But the means of several observers are very 

 different. They appear to leave in uncertainty some of the 

 most general questions arising : e. g,, the true mean for acid, 

 intermediate and basic rocks and the difference between the 

 radium content of primary and secondary rocks f. 



In this paper — which is preliminary in its scope — I shall 

 deal with general results rather than with details. Thus the 

 quesiion of ci magmatic differentiation" as an influence in 

 the segregation of radium I have put aside for the present ; 

 on that account leaving out determinations upon differentia- 

 tion products or what are believed to be such. The acid, 

 intermediate, and basic magmas, as represented by undif- 

 ferentiated plutonic, injected, or volcanic materials, are alone 



* Vide Eve and Mcintosh, Phil. Mag. Aug. 1907, and Trans. Royal 

 Society of Canada, 3rd series, 1910, p. 67. 



f A recent investigator has actually questioned if there is any such 

 difference, and points out that certain solution results on trachytes are 

 actually lower than his own results on limestones. Liichner, Konink. 

 Akad. ran Wetenschappen te Amsterdam, Jan. 1911. 



2 Z2 



