158 INTRODUCTION TO GENERAL SCIENCE 



in an inverted test tube. If this explodes, collect successive 

 tubes until the hydrogen so collected burns quietly. Then 

 light the hydrogen at the tip. The yellow color of the flame 

 is due to the sodium in the glass. 



Hold beaker of water, which is dry on the outside, but 

 filled with cold water, in the flame, and notice the large 

 amount of water which collects from the combustion of the 

 hydrogen. This also proves that water is composed of 

 hydrogen and oxygen. 



115. SOLUTION AND ITS EFFECTS 



We are inclined to think of solution as the disappearance of 

 a solid within a liquid. While this kind of solution is most 

 common, it is better to look upon solution as the uniform mix- 

 ture of the particles of one substance throughout the particles 

 of another substance. We can have a solution of a gas within 

 a gas, called diffusion; of a gas within a liquid, called absorp- 

 tion; a gas within a solid, called occlusion; of a liquid within 

 a liquid, called diffusion; of a liquid within a solid, called 

 water of crystallization ; and of a solid within a solid, called alloy. 



If a solid is dissolved in a liquid, the boiling point of the 

 liquid is raised, while the freezing point is lowered. Thus the 

 addition of common salt to water enables a cook to boil the 

 food at a slightly higher temperature, which may be desired 

 in some cases. Likewise, the addition of salt to ice produces 

 a mixture which has a lower temperature than the ice alone. 

 The salt causes the ice to melt, and the necessary heat is taken 

 from the solution. The latter does not freeze on account of 

 the salt. 



Platinum absorbs hydrogen and combines it with oxygen 

 at its surface so rapidly that the heat is sufficient to raise 

 the hydrogen to its kindling temperature. Automatic gas 



