A YEAE IN SCIENCE 63 



sulphuric acid solution. Put the block of wood across 

 the tumbler with the free ends of the metals dipping 

 into the acid. Eecord what happens. Are there any bub- 

 bles of gas given off? From where do they come? 

 Touch the free ends of the copper wires to your tongue. 

 What effect do you notice ? What is the evidence that 

 an electric current is passing through the wires ? Twist 

 the free ends of the wires together and hold them over 

 the compass. How is the compass affected? Is there 

 evidence of an electric current? Eecord all of your 

 observations. Find out from some source what is the 

 origin of the electric current. 



Exercise 37. Composition of Water. (Demonstra- 

 tion.) 



Object: To determine the composition of water. 



Apparatus 



Electrolysis apparatus Pine splinters 



Sulphuric acid (5%) Belljar 



Electric current 



Directions: Fill the apparatus with water con- 

 taining 5% sulphuric acid. When the apparatus is 

 almost filled, into each arm insert the burette, at the 

 same time opening the cock to drive out the air. After 

 the burettes are completely filled, connect the positive 

 and negative poles of the series with the city current. 

 Note what happens. From what place do, the bub- 

 bles arise ? In which tube do they form more rapidly ? 



What is the ratio by volume of .the , gases in t the 



