ARTICLE XXXH.— ON THE RADIUM CONTENT OF CERTAIN IGNEOUS 

 ROCKS FROM THE SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



By C, CoLEKiDGE Parr, D.Sc, and D. C. H. Florance, M.A., M.Sc. 



Rutherford (" Radio-active Transformations ") has calculated that 4-6 x 10~^* 

 gramme of Radium per unit mass of the earth would generate an amount of 

 heat equal to that lost by the earth by conduction through its crust. Strutt 

 (Proc. Roy. Soc, 1907) has examined the radium content of a number of igneous 

 and sedimentary rocks, and his results, corrected by Eve and Mcintosh for an error 

 of standardisation, give for mean values, igneous rocks, 1-7 xlO"-^^; sedimentary 

 rocks, 1-1x10"^^ — a result which is about twenty-eight times as large as the 

 theoretical quantity. Eve and Mcintosh (Phil. Mag., Aug., 1907) find a mean for 

 igneous and sedimentary rocks of 1-1 x 10~^^ per gramme of rock. Joly ( " Nature," 

 Sept., 1908) finds values much higher than these, his mean for igneous rocks 

 being 6*1 xlO^^^, whilst the mean content of the basalts examined by him was 

 5-0 X 10"^^ gramme per gramme of rock, which is much higher than that found by 

 other investigators for similar rocks. 



METHOD OF TESTING. 



The rocks examined by us were ground to a very fine powder, and 20 grammes 

 were fused in a platinum crucible with ordinary fusion mixture, 1 gramme of the 

 powdered rock being mixed with 6 grammes of the mixed carbonates, which had 

 been previously tested for radium. The fused mass was dissolved partly in dis- 

 tilled water and partly in HCl, both of which were separately examined. The acid 

 and alkaline solutions were then separately corked, with glass tubes and clipped 

 rubber connections in position, the cork coated with sealing-wax to prevent pos- 

 sible leakage of the emanation, and the flasks were then set aside for three weeks 

 to mature. The apparatus was similar to that described by Strutt {loc. cit.). The 

 solution was boiled for one hour, the steam being condensed in a Liebig condenser, 

 and the gases evolved being collected over freshly distilled water. Before the boiling 

 was stopped the water in the jacket of the condenser was run ofl, and steam was 

 passed through as far as the collecting-vessel to drive over the last traces of emana- 

 tion. The electroscope was similar to that used by Boltwood (" American Journal 

 of Science," 1904), and it was exhausted to half an atmosphere by means of an oil- 

 pump before any of the collected gases were passed in. These gases'were allowed 

 to enter very slowly through CaCl2 and II2SO4 drying-tubes, and the;^, pressure was 

 then brought up to atmospheric by the admission of air, the time occupied over this 



