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EXERCISE 28 



IS WATER A SIMPLE SUBSTANCE, OR IS IT COMPOSED OF MORE THAN ONE 



SIMPLE SUBSTANCE? 



Materials. A bottle with the bottom removed ; a two-holed stopper fitting the bottle, holes in 

 the stopper permitting the passage of platinum wires or carbons through them ; copper wire ; three 

 or more dry cells ; sulphuric acid ; two test tubes. 



Directions. This experiment is best performed by the teacher. It is most 

 conveniently done by the aid of a standard electrolysis apparatus such as is 

 furnished by the various laboratory supply firms. If no such apparatus is at 

 hand, the one shown in the diagram may be prepared. 



Partly fill the jar with a solution made by adding one part of concentrated 

 sulphuric acid to sixty parts of water. 1 Fill the two test tubes with the same 

 solution and invert them over the ends of the wires without admitting any air. 

 Attach to the free ends of the wires a battery of three or more dry cells con- 

 nected in series, and observe what happens. Allow the gases that are given 

 off to collect in the test tubes. Note the relative volumes of the contents of 

 the two tubes. When the tube containing the greater volume of gas is nearly 

 full, disconnect the batteries and remove this tube, placing a finger over the 

 open end of the tube and keeping the mouth of the tube downward. Bring a 

 lighted match to the mouth of the tube and note the popping noise and the 

 pale-blue color of the flame. The gas which was in this tube was hydrogen. 



Remove the second tube carefully and test the collected gas by thrusting 

 a glowing, not flaming, pine splinter into the mouth of the tube. Observe what happens. This gas 

 is oxygen. 



Considering that the amount of sulphuric acid is not lessened even if the current is allowed to 

 pass for a long time and therefore cannot be the source of either gas collected, write your notes and 

 answer to the question of this exercise. 



NOTES. If this experiment is performed in a laboratory fitted with a direct-current electric-lighting 

 circuit, the proper current may be obtained by passing it through one or more sixteen-candle-power lamps. 

 If more than one is used, they should be arranged in parallel. 



If wire nails are used instead of platinum wires or carbons, it must be kept in mind that the acid will 

 probably act upon the iron, and the results will be less satisfactory. 



1 Always add the acid to the water, never in the reverse order. 



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