720 



used by ine the principle of which was published in 1914. ^) while 

 the description of the apparatus followed in a second article. *) 

 The method of measuring I arranged as follows : 

 Before making the solution boil the electrometer was given a 

 definite not over-sensitive state of charge and that : a -|- 12 Volt, 

 h Volt, c upwards of — 4 Volt. The ionisation cylinder was 

 charged to -}- 80 Volt. ') Having attained this, the natural leak in 

 the measuring cylinder was examined a couple of times. The time 

 was so fixed as to make 10 scale-divisions move under the cross 

 wire until the total of one hundred divisions were passed through ; 

 this happened in order to be able to include into the calculation 

 the natural leak, when measuring the samples. After this the ioni- 

 sation space of the apparatus was exhausted, making useofGAEDE's 

 new single barrel airpump; with this it was possible to exhaust the 

 space of them easuring cylinder of a volume of 1 litre with the indispens- 

 able rubber tubing and manometerspace down to two mm. pressure. 

 The emanation present in the bottle, after having been conducted 

 through drying-tubes with CaCl,, P2O5, and a lube with cotton wool, 

 was transferred to the evacuated apparatus. After having awaited 

 the equilibrium of the emanation with the radio-active products, 

 radium A. B. C, so after about 3 — 4 hours, the measurement proper 

 took place as follows : the time was fixed in which the image of 

 the scale moved under the cross wire, but now, in contradistinction 

 with the determinations just given, over 150 scale-divisions; as this 

 measurement did not last for more than 5 minutes for a sample 

 that is but little active, and also the preceding, viz: that of the 

 natural leak took comparatively little time, the advantage had been 

 obtained by repeating the measurement a couple of times, to be 

 able to include into the average calculation a more exact final 

 value. Herewith the determination proper had come to an end and 

 the radio-activity of the substance could be computed by taking an 

 experiment of the same kind with a normal solution of radium. 

 This I obtained fi-om a quantity of radiumbariumbromide supplied 

 by Messrs. de Haen in Hannover, containing 0.0126 m. grammes of 

 radium according to notification. 



Here follows, by \vay of explanation, a calculation of one of the 

 samples examined, viz: N°. I from Betjenskelder. 



a. Determination of the natural leak. 



^) Royal Acad, of Sciences. Amsterdam. Proceedings of June 1914. 



2) Royal Acad, of Sciences. Amsterdam. Proceedings of September 1917. 



3) Royal Acad, of Sciences. Amsterdam. Proceedings of June 1914. 



