1904.] 



certain Minerals and Mineral Waters. 



195 



emanation. It proved to be identical with the rate of decay of the 

 emanation of radium.* The activity is wholly due to that element. 



This deposit was collected inside the King's Well itself, where the 

 hot water issues from the ground. Other deposits are left in the tanks 

 and pipes. They are less active than that collected near the source. 



Deposits from another of the hot springs at Bath, that known as the 

 Old Royal Spring, have also been tested. These were found to be 

 active also. In this case there was no opportunity of collecting the 

 deposit at the well-head itself, but it was found that the deposit left in 

 the channel near the source was more active than that in the tanks 

 further from it. 



It was interesting to determine whether the water itself contained 

 any radium in solution. There could be little doubt that there must 

 be traces left in solution, after the deposit had settled out. But, 

 since the Bath water contains abundance of sulphates, and since 

 radium sulphate is one of the most insoluble salts known, there could 

 not be more than the merest traces present. The sulphate of barium 

 is very much less soluble than that of strontium. And presumably 

 the sulphate of radium is much less soluble still. Barium sulphate 

 requires half a million times its weight of water to dissolve it ; radium 

 sulphate perhaps several hundred million times its own weight. 



About 10 litres of the Bath water were evaporated to dryness. The 

 resulting saline residue was sealed up in a hard-glass tube, and left 

 for about a fortnight to generate a stock of emanation. On heating, 

 a distinct emanation was obtained, giving several times the rate of leak 

 that air did. A deposit, similar to that from the Bath water, but 

 black in colour, can be collected from the source of the hot springs 

 of Buxton. It has been analysed by Dr. J. C. Thresh,f and I am 

 indebted to his kindness for a specimen of it. This deposit was found 

 to contain radium also ; the proportion present being not very 

 different from what was found in the case of some of the Bath deposits. 



The following table gives the quantitative data for these emanations 

 from these deposits. The rates of leak are on the same scale as those 

 in the preceding table. 



It will be seen that the richest of the deposits is some thirty-six 

 times more active than the salt obtained by evaporating the water. 



Although the agreement in the rate of decay of the emanation 



* In the first experiment made, I obtained a small residual leak when the 

 radium emanation had decayed. This was attributed to a new emanation, of 

 greater durability. But I have failed to repeat the experiment, and am forced to 

 conclude that the leak was due to a failure of the quartz insulation, owing to the 

 presence of moisture. It is very difficult to understand how this can have 

 happened, for the gas was passed through drying tubes. When the rate of leak 

 was tested with air in the apparatus, it had always a perfectly definite and 

 constant small value. 



f * Proc. Chem. Soo.,* January 17, 1882. 



