1028 



Voltaic Electricity. Section 9: Electron Theory and Radioactivity. 



No. 63 181 



63 181. 1 : 4. 



63 184. 1 : 4. 



63 182. 1 : 6. 



63.181. Electrometer, Figure, specially arranged for investigating radioactive substances. 



The apparatus corresponds to a Kolbe No. 61,096 Aluminium Leaf Electrometer, p. 802, and has 

 a projection-calibration scale and amber tube in ebonite plug, one extra ebonite plug with amber tube, 

 conductor rod and paper leaves. The instrument has a small stage at the side on which are placed 

 the substances to be investigated. 



The electrometer is charged by influence by allowing an ebonite rod, electrified by friction, to 

 act on the upper plate. The aluminium leaf is deflected from its perpendicular position and conserves this 

 deflection for a very long period, provided no radioactive substances are allowed to act on it. If, 

 however, radioactive substances in the form of fine powder are placed in a thin layer in a special sheet 

 iron plate, and put on the lower slab, the rays emitted render the air between the two plates conduc- 

 tive, thus discharging the electrometer. The velocity with the which the aluminium leaf moves during the 

 discharge gives a measure for the intensity of the radiation of radioactive substances. 



63.182. Electrometer after Curie, Figure, on wood stand, with reading microscope . . 



The Electrometer is built into a metal housing covered by two glass plates. The two horizon- 

 tal metal plates are covered by a cap, this being removed when introducing the substances and replaced 

 for carrying out the 'measurement. This part of the apparatus can be easily cleaned and any trace 

 of dust of radioactive substances should be avoided. The electrometer proper is well closed, since 

 the necessary cleaning would be attended with difficulties. The electrometer is charged at the upper 

 knob, protected by a special cap. For taking the substances to be introduced special small plates 

 are supplied with the apparatus. 



In order to estimate the velocity of the leaf the lower and of the same should be observed by 

 means of the fixed microscope having micrometer ocular. With the aid of a seconds clock the linn- 

 is noted which is necessary for the image of the front edge of the leaf in the micrometer to move 

 over a definite number of divisions. 



63,183. idem, without reading microscope 6. 0. 



s. d. 

 4. 0.0 



7. 10. 



63,184. Simple Portable Electroscope for investigating weakly radioactive substances, 



Figure 2. 0. 



Cl. 2078, 



6114,3699. 



