146 Prof. J. Joly on a Method of Investigating the 



which had been dealt with by the solution method in his 

 experiments on the Leinster Granite (Phil. Mag. Jan. 1901). 



The increase is 44 per cent. This, however, does not quite 

 give the full increase. A low result by solution (1*14) on the 

 Ballyellin granite was also obtained, and again the highest of 

 3 results is cited above in the case of the Glencullen granite 

 solution. Allowance for this would raise the percentage 

 increase by the new method. It is a striking fact that the 

 Aughrim result is based on four repetition experiments on 

 the one solution, giving precisely the same result, and yet the 

 fusion method raises it by 66 per cent. The Blackstairs'result 

 is based on two identical determinations of the emanation in 

 the solution. The agreement with my own results on some 

 of these rocks by use of the other furnace is close. 



In calculating the above results obtained by the tube- 

 furnace, special experiments on the calibration constant 

 proper to the furnace were made by Mr. Fletcher. Two are 

 by addition of the uraninite before mentioned to the Blackstairs 

 granite : — 



0*34 mgrm. uraninite in 6 grm. granite, C = 0*62 x 10" 12 

 0*60 „ „ „ „ = 0-57 xlO" 12 



On the strength of these results the constant would appear 

 to be about 0*6 x 10" 2 , and this value was taken for the 

 foregoing determinations. The following calibration obser- 

 vations made on two standards which I had prepared some 

 months previously are of interest : — 



(1) A quantity of radium in solution =15*7 x 10" 12 grm. 

 was added to 7 grms. of boracic acid. The mixture was dried 

 over the water-bath and fused to a clear glass which was 

 pulverized and preserved in a closed tube. 



For the experiment this powder was added to 6 grams of the 

 Glencullen granite mixed with the alkaline carbonates. The 

 fusion gave C = 0'73 x 10~ 12 . 



(2) One milligram of uraninite in solution, taken from the 

 standard solution of the Joachimsthal ore, was added to 

 7 grms. of powdered Glencullen granite. This was then 

 dried over the water-bath, mixed with carbonates, and fused. 

 The melt was pulverized, weighed, and put by in a closed 

 tube. 



For the experiment 4 grams of this melt was added to 

 5 grams Killiney granite along with 24 grams carbonates. 



Calculated directly, by deduction of the increased leak 

 due to the granites present, the constant is found to be 

 O = 0'72 x 10~ 12 ; which is in close agreement with the result 



