ELECTROMAGNETS 



47 



the water is stirred until the solid is dissolved. A clean wooden 

 stick, whittled into the form of a paddle, makes a good stirring 

 rod. The upper level of the solution should be at least 5 cm. 

 (2 in.) below the top of the jar before the zinc and carbon are 

 put in. 



6. Find out where in your house the battery for the electric 

 bell is placed, and get help, if necessary, to take it out, so that 

 you can examine it. Describe it in your notes, giving the 

 commercial name, the name of the manufacturer, etc. 



How much did your house battery cost per cell? Find out 

 how long the stick of zinc lasts, and how much a new one costs. 

 What is the "life" of the sal ammoniac solution, and how much 

 does a new charge of sal ammoniac cost? 



c. If your doorbell is operated by "dry" cells, get all the 

 data regarding them, and write 



the data in your notes. 



d. If your doorbell is -operated 

 by a battery of two or more cells, 

 notice how they are connected. 

 If the carbon of one cell is con- 

 nected with the zinc of the next 



Cell, aS in Fig. 134, 159, Of the Three Cells Connected "In Parallel" 



text, the cells are said to be con- 

 nected in series. If all the carbons are connected with one 

 wire, and all the zincs with the other wire, as in Fig. 21, the 

 cells are said to be connected in parallel, or abreast. 



EXERCISE 46 

 ELECTROMAGNETS 



Apparatus and Materials. Sal ammoniac cell, insulated wires, 

 magnetized needle or compass, soft iron bar or wire nail, for a core; 

 iron filings, tacks, and nails. 



