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A Convenient High Potential Battery. 



By R. R. Ramsey. 



In work ou radioactivity it is necessary to liave a battery whose poten- 

 tial is lOO volts or more. If one lias access to a direct current lighting 

 circuit a storage battery made of test tubes with sheet lead strips for 

 electrodes can be used. Fifty such cells arranged in a rack make a con- 

 venient battery when the lighting circuit is 110 volts. Such a battery re- 

 quires a week or more for forming, and due to the small capacity of the 

 cells they Should be connected to the charging circuit all the time except 

 when in actual use. When it is not convenient to make such a battery, or 

 when the facilities for keeping it charged are not at hand, I have found 

 that a battery can be made with little trouble and expense of txibular flash 

 lamp batteries. The so-called 3A volt flash lamp batteries consist of three 

 small dry cells slipped into a pasteboard tube. The bottom of the cell is 

 the negatiA'e terminal, while the central carbon has a projection extending 

 through the top, which serves as the positive terminal of the cell. Thus 

 the three cells when placed in the tube are in series. If the cells are 

 slipped down through the tubes until the bottom ones project one-half their 

 length the batteries can be placed one on top of another and form a long 

 battery connected in series, the potential of which depends upon the length. 

 The so-called 3^ volt battery when new has an E. M. F. of about 4.4 volts. 

 Or twenty-five such batteries in series give 110 volts. Of course it is not 

 necessary to connect all in one "stick." They can be placed in "sticks" o> 

 convenient length and placed upright in a box and connected in series by 

 soldering wires to the ends, thus making connections which will give in- 

 termediate potentials. When new these batteries have very low resistance, 

 and great care should be exercised to prevent short circuiting the cell. Like 

 all dry cells the resistance increases with age and the potential at the ter- 

 minals as shown I>y a Vdltmeter will decrease. I'.ut the E. M. F. of the 

 cells as shown by itolcnlioinetei' measurements remains constant until the 

 cells are completely dried out. Since the battery in radioactivity work is 



