Oxygen 255 



occurs has shown that the oxygen is supplied by the 

 potassium chlorate and that the manganese dioxide is 

 apparently unaltered during the experiment, being 

 recoverable from the residue in the test-tube unchanged 

 in quantity. Many similar reactions are known in 

 which a substance causes the result of a reaction to be 

 brought about more readily but itself appears to under- 

 go no change. The learned name given to this pheno- 

 menon is "catalysis", which means "decomposition 

 by contact". Because we have this name in our 

 memories, however, we must not think that we know 

 more about the peculiar nature of the action. Up to 

 the present no perfectly satisfactory explanation of 

 why the manganese dioxide should help the potassium 

 chlorate to give up its oxygen has been put for- 

 ward. 



1 74. With the oxygen obtained as above, the follow- 

 ing experiments should be performed. 



EXPERIMENT 112. Insert a glowing splint of wood 

 into one jar. Observe the brightness of the flame pro- 

 duced. Into the same jar, if all the oxygen be not 

 used up, introduce a lighted candle on the end of a 

 piece of copper wire. Observe the decrease in size and 

 the gain in brightness of the flame. 



Exercise for Student. 



How do you explain the smaller size of the flame of the candle 

 when it burns in oxygen ? 



EXPERIMENT 113. Burn coal-gas from a small glass 

 jet in a second jar of oxygen by means of the arrange- 

 ment indicated in the figure. Note any changes in the 

 nature of the flame. Should the heat produced 

 be sufficient to close the jet by melting the edges of 

 the glass together, another tube may be prepared 



