184 Life and Matter [chap. x. 



substance is apt to be extruded again when 

 the liquid cools, and when the affinity of the 

 water-aggregates for each other resumes its 

 sway. Very hot water can dissolve not only 

 the substances familiarly known to be soluble 

 in water, but it can dissolve things like glass 

 also; so that glass vessels are unable to retain 

 water kept under high pressure at a very high 

 temperature, approaching a red heat. 



Another material which also seems to 

 have the power of combining with a 

 number of other bodies, under the influence 

 of the loose mode of chemical combination 

 spoken of as residual affinity, is carbon ; so 

 that a block of charcoal can absorb hundreds 

 of times its own bulk of certain gases. 



Indeed, Sir James Dewar has recently 

 employed this absorbing power of very cold 

 carbon to produce a perfect kind of vacuum, 

 which may, perhaps, be the nearest ap- 

 proach to absolute vacuum that has yet 

 been attained : probably higher than can be 

 attained by any kind of mechanical or 

 mercury pump. 



