74 SCIENTIFIC AMUSEMENTS. 



CHAPTER VI. 



SOLUTION OF GASES IN LIQUID SOLVENTS AND SEPARATION OF 

 GASES FROM SOLUTION, NO CHEMICAL ACTION TAKING 

 PLACE. 



In some of the previous experiments we have seen that besides 

 ordinary air (which is obviously different in many respects from 

 coal-gas) a number of substances can be obtained by chemical action 

 resembling air and coal-gas in the one respect of physical texture, 

 but otherwise considerably different not only from these two 

 substances, but also from each other. Thus hydrogen (Expt. 10), 

 and sulphuretted hydrogen (Expt. 13), obtainable as above described, 

 are specimens of a much larger number of similarly-textured 

 substances obtained by means of various chemical changes, all of 

 which are generically grouped together as Gases. 



Strictly speaking, all gases are really the steams or vapours given 

 off from so many highly volatile liquids, just as actual steam or 

 water vapour (Chapter III.) is given off on boiling water, and 

 differing from ether vapour as regards volatility in much the same 

 way as ether vapour differs from water vapour, or water vapour 

 from mercury vapour ; just as by chilling any one of these vapours 

 the substance resumes the liquid condition, so may any one of the 

 gases known to chemists be condensed to liquids by sufficiently 

 lowering the temperature ; but in some cases the amount of chilling 

 required is so great that it was only within a few years that 

 scientific appliances became sufficiently perfected to enable this to 

 be done \ previously to that, although it was inferred by analogy 

 that all gases could be condensed to fluids under proper conditions, 

 still some half dozen (of which hydrogen was one) had resisted all 

 attempts to liquefy them, and were accordingly known as the 

 " incondensible gases." At present no such distinction is recog- 

 nised; and a "gas" simply means a vapour requiring a lower 

 temperature to condense it to a liquid than the ordinary atmo- 

 spheric temperature in temperate climates. Sulphur dioxide, 

 indeed, liquefies at but little lower than the freezing point of water ; 

 and both this gas and another comparatively easily liquefiable one, 

 ammonia, are employed for various purposes in the arts in the 

 liquid state.* 



* Principally for freezing machines, in which they are employed in some- 

 what the same sort of way as in Expt. 46. 



