66 ELEMENTS OF GENEBAL SCIENCE 



68. Water produced by a flame. If a cold object, such as a 

 piece of iron or a test tube full of water, is held in the flame, 

 soot may collect on it. We shall not give attention to the 

 soot for the present. Another thing that we shall find in the 

 flame is not ordinarily expected. Drops of water collect 

 upon the cold object ; but if the object is allowed to get hot, 

 the water evaporates again. The water came from the flame 

 and was formed in the flame. Furthermore, if a gas flame is . 

 used instead of a candle flame, and every precaution is taken 

 to make sure that there is no water vapor either in the gas 

 or in the air, the same result follows. Since this water was 

 produced from substances other than water, it is important 

 for us to know what changes and what substances have pro- 

 duced it. The best way to find what substances compose 

 water is to find what results when water is decomposed. It 

 is not easy to determine what the component parts are, and 

 we shall have to use experiments directly related to that 

 problem. These experiments require the use of an electric 

 current, which we shall study later, but at this time we 

 shall give our attention to the composition of water. 



69. Composition of water. When we put the ends of two 

 platinum wires in water and pass a current of electricity 

 through the water between the wires, it is noticed that bub- 

 bles of gas arise from both wires. By suitable apparatus it 

 is possible to collect these bubbles until there is enough gas 

 to allow us to examine it (fig. 37). It will be noticed that 

 the volume of gas that may be collected from one wire is 

 about double that collected from the other. Both gases are 

 colorless and look like air. One of them, that of the greater 

 volume, takes fire and burns with a pale blue flame ; the 

 other does not take fire, but a splinter burns much more 

 brilliantly in it than in the air. The one which takes fire is 

 called hydrogen; the one which makes other things burn 

 more brilliantly is oxygen. They can be caused to unite, and 

 when they do so they form water. We may conclude th*fc 



