MAGNETISM AND ELECTRICITY 171 



piece of iron ; then try other substances. Since the wire 

 is copper (not iron), what seems to be a characteristic of a 

 wire in which a current of electricity is passing? 



6. Repeat the tests upon the compass needle, but this 

 time use a dry cell with its binding posts connected by cop- 

 per wire. State the results, and their significance. 



7. Cut the wire, joining the binding posts of the dry cell, 

 in the middle, and test the effect on the compass needle of 

 the wires of the " broken circuit." Bring the ends of the wires 

 together on either side of a thickness of paper, and determine 

 if the current completes a circuit through the paper. 



8. Connect the ends of the wires fastened to the binding 

 posts of the dry cell to the binding posts in the cap of an- 

 other simple cell into which two copper strips have been 

 fastened. These copper strips are now the terminals of a 

 broken circuit. Put these strips down into a second tumbler 

 containing some water, being careful to keep them near 

 each other but not touching. By bringing one of the con- 

 necting wires down over the compass needle at rest, de- 

 termine if the circuit has been closed through the water. To 

 the water add a little sulphuric acid and, after stirring the 

 liquids well, test the effect of the wire on the compass anew. 

 The acid serves as a carrier of electricity across from one 

 terminal to the other, and is said to be an electrolyte. Many 

 substances in solution would behave in a similar manner, but 

 not all solutions are electrolytes*. 



9. Repeat paragraph 8, but this time use with the water 

 a little copper sulphate (CuSO 4 ) for the electrolyte. After 

 some time with the circuit closed examine the copper plates 

 for changes in appearance. 



