Radioactivity of Mineral Springs. 149 



In this case the deviations of the aluminium leaf were read 

 by means of a microscope containing a micrometer eyepiece, 

 the measurements being made by observing the time taken 

 by the aluminium leaf to fall from a determined scale- 

 division to another : this method has the advantage of insur- 

 ing a constant sensibility of the apparatus throughout all the 

 observations. 



The readings were reduced to the potential fall in volts 

 per hour, the effects due to the natural ionization of the air of 

 the room and to the imperfections of insulation being each 

 time subtracted. 



Ten grams of each material, reduced into a fine powder 

 and uniformly spread on the dish, so as to form a very thin 

 layer, were successively tested in the apparatus, with the 

 results that follow (see Table, p. 150). 



The effect due to an equal weight of uranium nitrate is 

 given as a term of comparison. 



As one can see, the activity of the different sediments 

 deposited by the waters diminishes greatly with the increasing 

 distance between the spring and the spot at which they are 

 formed. A similar observation had already been made by 

 Elster and Geitel with the deposits of Baden. 



I have noted a curious fact in connexion with this at the 

 so-called " Source d'Alun " of Aix-les Bains ; the waters 

 there show at their surface a viscous substance, partly 

 organic, called " Baregine/' which has a considerably greater 

 activity than any other material that I could collect in this 

 particular spring. The theory of the origin of this substance, 

 as given by naturalists, states that it is formed at the spot 

 where the waters emerge from the soil. 



I had noted that by keeping some of the sediments for a 

 certain time in the testing-vessel the conductivity of the air 

 inside steadily increased until it reached a maximum. This 

 being evidently due to the formation of a radioactive emana- 

 tion. I undertook to determine its rate of decay. 



The apparatus which I used for this purpose is represented 

 in iig. '2 (p. 151). 



A certain amount of the sediment to be tested was intro- 

 duced into a flask F and left there for some days, the flask 

 being heated from time to time. Then the two stopcocks 

 S 2 and S 2 were opened and air was drawn by means of a 

 water-pump from F through a wash-bottle W containing 

 sulphuric acid, a tube P containing phosphoric pentoxide, 

 and a bulb B tightly packed with glass-wool, into the testing- 

 i V, after which the stopcocks 8 8 and S 4 were carefully 

 closed. 



