9o 



CHEMISTRY. 



mixture of carbonic anhydride and hydrogen 

 in both bottles. A part of the carbonic anhy- 

 dride has gone up into the upper one, and a 

 part of the hydrogen has come down into the 

 lower. This is because, for some reason, there 

 is a strong disposition in the two gases to 

 mingle strong enough to overcome the force 

 of gravity which tends to keep them separate. 

 And notice that in this case gravity must op- 

 erate very strongly indeed, for hydrogen is the 

 lightest of all substances, while carbonic an- 

 hydride is a very heavy gas. If, then, the dis- 

 position of gases to mingle overcomes so readi- 

 ly in this case the force of gravity, much more 

 readily will it do so when we have carbonic 

 anhydride with oxygen and nitrogen, as in the 

 air, where the difference in specific gravity is 

 so much less. 



121. An Analogy- There are some liquids 

 which have a disposition to mingle together in 

 the same way that gases do. Thus water min- 

 gles readily with alcohol, with the various 

 acids, etc. Alcohol is lighter than water, as 

 oxygen is lighter than carbonic anhydride, and 

 therefore, in obedience to gravitation, the water 

 inclines to keep below the alcohol, and would 

 do so if the disposition to mingle were not 

 stronger than the influence of gravity. In the case of oil 

 and water there is no disposition to mingle, and therefore 

 gravitation acts without any impediment, keeping the water 

 under the lighter oiL Agitation promotes the mingling of 

 both liquids and gases. Alcohol can be poured so quietly 

 upon water that it will remain for some little time. This can 

 be made obvious by having the alcohol colored. They will 



