6 ELEMENTARY PHYSIOLOGY. I. 



c. Accumulator (Fig. I a). The positive pole is 

 coloured vod, >nd the negative pole black. The screws 

 ' on the top are for charging the cell and should not be 

 touched. These are connected through a resistance with 

 binding screws A and B, from which current should be 

 taken. 



Hold the ends of a voltmeter on the top screws. The 

 voltage should be about 2; if it fall to 1-8 the accumu- 

 lator requires recharging. Test the voltage of the current 

 taken from screws A and B and that of a Daniell and 

 a, Leclanche cell. 



Note the electrodes (Fig. 1 6), consisting of two in- 

 sulated German silver or platinum points bound to- 

 gether and soldered on to insulated copper wires. The 

 wires are differently coloured (or the beginning and end 

 of one is marked), so that the wire connected with each 

 electrode can be recognised. When it is required to fix 

 the electrodes to cork, two pins are passed between 

 them as in Fig. 1 b. 



Connect the electrode wires with the screws A and B 

 (Fig. 1 a) and place the points on neutral litmus paper 

 moistened with water; the paper turns blue at the 

 negative pole or cathode, and red at the positive pole 

 or anode. 



Dip the points in dilute H 2 S0 4 (1 p.c.). Bubbles of 

 gas (hydrogen) are set free at the cathode. 



2. Switch (key). There are several forms of keys. 

 Fixed to the table are two bell switches, one arranged 

 for use as an in-circuit key and the other for use as a 

 short-circuit key. Screw off the brass cover of each and 



