A ConveNtIent High PorentiaL Battery. 
By R. R. RAMSEY. 
In work on radioactivity it is necessary to have a battery whose poten- 
tial is 100 volts or more. If one has 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 tubular flash 
lamp batteries. The so-called 33 volt flash lamp batteries consist of three 
small dry cells slipped into a pasteboard tube. The bottom of the cell is 
the negative terminal, while the central carbon has a projection extending 
through the top, which serves as the pesitive 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 34 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 by a voltmeter will decrease. But the I. M. F. of the 
cells as shown by potentiometer measurements remains constant until the 
cells are completely dried out. Since the battery in radioactivity work is 
