240 



ELECTRICITY 



cell a single unit for producing electrical energy from 



chemical energy. 



battery a group of electric cells connected together. 

 electrify to charge with electricity. 

 electron a negative particle of electricity. 

 insulator a non-conductor of electricity or heat. 

 lead peroxide a chemical compound of lead and oxygen 



used on one of the plates of the storage battery. 

 molecule the smallest bit of any substance which may 



still be recognized as that substance by its properties. 



For example, the smallest bit of wood which would 



still be called wood. 

 nucleus the central part of the atom. 

 proton a positively charged electrical particle in the 



nucleus of the atom. 



static electricity electric charges which are not in mo- 

 tion. 

 terminal a binding post on an electric cell or battery. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 1 



Experiment 146. How may electricity be produced by 

 rubbing? 



Secure two toy rubber balloons, blow them up, and sus- 

 pend them from a support. Rub a fountain pen or hard 

 rubber comb with a piece of fur and bring it near one of 

 the suspended balloons. Note what happens. Rub each bal- 

 loon briskly with the fur and observe what happens. Bring 

 your hand near one of the balloons. What do you observe? 

 Rub a balloon with fur and bring near it a fountain pen 

 also rubbed with fur. Observe the result. Rub one balloon 

 with the fur; then rub a glass rod or dish briskly with a 

 piece of silk and bring near the balloon. Record your results. 

 If the materials are available, rub sealing wax, sulphur, and 

 several metal rods with fur and bring them near a balloon 

 which has been rubbed. Observe and record your results. 



The balloon was (attracted, repelled) by the foun- 

 tain pen which had been rubbed with fur. When both bal- 

 loons were rubbed they seemed to (attract, repel) . each 



other. When the hand is brought near a balloon which has 

 been rubbed with fur, the balloon is (repelled, attracted) 



. A balloon rubbed with fur is (repelled, attracted) 



by a fountain pen also rubbed with fur. A balloon rubbed 



with fur is (attracted, repelled) . by a glass rod rubbed 



with silk. Metal rods rubbed with fur (do, do not) ___ in- 

 fluence the balloon. Sealing wax and sulphur when rubbed 

 with fur (attract, repel) the balloon. 



Experiment 147. How are dry cells constructed? 



Remove the pasteboard containers from an old and a 

 new dry cell and carefully study the condition of the zinc 

 can in each one. Record any differences noted. With a 

 saw cut lengthwise through the zinc can of the old cell 

 and then push the sides of the cut apart. Carefully observe 

 the inner construction of the cell, recording your notes in 

 your notebook. Remove the carbon rod from the center 

 of the cell and study it. What seems to be between the rod 

 and the zinc can? Does the carbon rod touch the zinc? 



The zinc of the old dry cell seemed to while the 



new one was not. Inside the zinc can were several layers 

 of , 



1 See workbook, p. 84. 



The carbon rod and zinc can (were, were not) in 



contact. The cell was sealed at the top with . Between 



the carbon rod and the zinc can there seemed to be a 



substance which was in color. 



Experiment 148. How is a storage battery constructed 

 and how does it work? 



Secure two pieces of lead about an inch and a half wide 

 and five inches long. Punch a hole through each piece with 

 a nail and attach a copper wire by inserting it in the hole. 

 Clean the plates with fine sandpaper or steel wool and place 

 them in a solution of four parts water to one part concen- 



FIG. 379 



trated sulphuric acid. Be careful to pour the acid slowly into 

 the water, and not to get any on your hands or clothing. 

 Attach the wires to an electric bell and note any results. 

 Now connect three dry cells together in series, that is, from 

 the carbon of one cell to the zinc of the next and so on 

 (Fig. 379). Connect these cells to your storage cell and care- 

 fully observe what happens. After the storage cell has been 

 charged for about ten minutes, disconnect the dry cells and 

 again observe the lead plates. Note any change. Again at- 

 tach the storage cell to the electric bell and observe results. 



Secure a worn-out storage battery from a garage and 

 tear it to pieces. Compare the parts with your simple cell 

 and find out wherein they differ. 



When the cell was first connected with the bell it (did, 



did not) ring. The plate of the storage cell connected 



to the carbon of the dry cell battery changed to a 



color. A was given off by the storage cell while it was 



charging. The lead plate connected to the zinc of the dry 



cell battery seemed (to, not to) change in color. The 



substance on the one plate probably came from the 



chemical action in the cell caused by the from the dry 



cells flowing through it. When the storage cell was again 

 connected to the electric bell, I found that the bell . 



Explain below how the simple storage cell which you 

 made is like a large storage battery and how it is different. 



OTHER INVESTIGATIONS WHICH YOU CAN MAKE 



1. Study the operation of a simple voltaic cell. 



2. Study the operation of an ammonium chloride cell. 



3. Visit a storage battery service station and secure all 

 the information possible about the testing, charging, and 

 care of storage batteries. 



4. Examine the storage battery on your car and, if pos- 

 sible, learn to test it. 



