-Rubber-covered wire 



EXERCISE 8 



Although water seems to be a simple substance, it has been found to be made up of still simpler 

 substances. 



Problem. How can we show that water is made up of simpler substances ? 



What to use. Have the teacher borrow 



.TO socket or batteries _ T-, ./..,, a eudiometer, or make one as shown in the 



diagram. A direct current from a general 

 circuit, from a storage battery, or from four 

 dry cells ; water ; sulfuric acid ; matches ; 

 splints. 



What to do. Set up the eudiometer or 

 the piece of apparatus shown. Over the 

 ends of the wires have two inverted tubes 

 full of water containing a small amount 

 of acid. 1 Turn on the current or complete 

 the circuit until one tube is full of gas. 

 Note the changes that take place in each 



tube. Remove and invert each tube and treat with a burning match, then with a glowing splint. 

 Record. Describe what happened after closing the circuit. If dry cells are used, decide whether 

 more gas is given off at the carbon (+) or at the zinc ( ) pole of the battery. If a storage battery is 

 used, note whether more is given off at the + or at the pole. 



Questions. 1. In what ways are the two gases alike? 



2. (a) Which gas burns ? (b) What is formed by the burning ? 



3. How can you recognize the other gas ? 



NOTE i . Water is broken down into two parts. The one of which the volume is larger is called hydrogen. The other 

 is called oxygen. 



NOTE 2. Water, up to the present time, has never been divided into simpler parts than oxygen and hydrogen. We 

 cannot break up oxygen into anything simpler than oxygen, nor hydrogen into anything simpler than hydrogen. A sub- 

 stance such as oxygen or hydrogen, gold, silver, chlorin, which we have not been able to break up into simpler kinds of 

 matter, is called an element. A chemical combination of two or more elements is called a compound. 



1 Pure water will not conduct the electric current; but with acids or some other substances dissolved in it, water is a 

 conductor of electricity. 



[8] 



