Radioactivity of the Leinster Granite. 105 



of emanation extracted on subsequent ebullition of a solution, 

 a series o£ thirteen redeterminations were made after the 

 solutions had been stored during a further period of four 

 months. The results were quite satisfactory, no tendency 

 either to a lowering or a raising of the original determinations 

 being apparent. In six of these cases the subsequent experi- 

 -ments yielded figures identical with those originally arrived at. 

 In the case of the granite from Aughrim four determinations 

 yielded the same figure. For the remainder the subsequent 

 results vary but slightly from the original ones with the 

 single exception of No. 17. Every effort was made to expel 

 all the emanation by a vigorous ebullition, which was forced 

 until the steam condensed in the receiver globe. Finely 

 powdered talc spread over the inner surface of the condenser 

 tube served as a perfect indication of the maximum height 

 of condensation. 



The following table (p. 106) has been arranged with a 

 view to bringing together results obtained upon specimens 

 from the same locality. 



Some attempt was made to determine whether the radio- 

 activity could be assigned to any particular constituent, or 

 whether the distribution was uniform throughout the mass. 



A coarse granite from Ballyellin- — No. 17 in the accom- 

 panying table, — bearing the typically porphyritic muscovite 

 with included biotite, was chosen. The flakes of biotite when 

 they appeared in the muscovite showed pleochroic ha Jos 

 and much irregular radioactive darkening. The granite was 

 coarsely broken and about three grams of mica crystals 

 extracted. An examination of this yielded for the radium 

 present per gram the figure 4*48 X 10~ 12 gr. The original 

 granite from the same hand specimen yielded a quantity 

 2'08 x 10~ 12 gr. per gr., and assuming the mica to be about 

 20 per cent, of the whole mass (Haughton), it follows that 

 the mica was responsible for about 1 X 10 -12 gr. per gr. of 

 the granite, or about ^ of the who!e quantity contained. 



Professor the Hon. P. J. Strutt found (Proc. P. S. lxxviii. 

 A. p 150) that in one gram of Cornish granite over one half 

 (approximately -J) of the radium present, was confined to the 

 brown mica and the heavy minerals contained in it. Generally 

 speaking, this relation therefore seems to hold good in the case 

 of this granite. 



An examination of massive quartz, felspar, and muscovite 

 mica, free from biotite inclusions, all from large crystals 

 found in the neighbourhood of the Three Rock Mountain, 

 yielded respectively 0'00, 0'52, and 0*72 gram per gram for 

 their contained radium. The mica havino- the radium content 



