ON MIXED CA&SS. 'ZlO 



The propofition refpeaing the mechanical aftion of ah" on ^^^^^^^'^"^^^ 

 the furface of water, will be anfwered by Mr. G. when he jg^ter on"mixcd 

 has proved that air has no pores, or no capacity for the re-gafes. 

 ception of water. For, nothing can be more clear than that, 

 whatever may be the preffiire of the atmofphere, and how- 

 ever few the points of its action, water cannot be forced into 

 the pores of air, if it have none. 



Mr. G. proceeds to (late two new fa6ts, which are faid to 

 be inexplicable on my principles : I muft undertake the ar- 

 duous talk. The fads are, 1^, Air containing aqueous va- 

 pour is fpecifically lighter than air without it, cateris paribus ; 

 and, 2d, A bottle internally moift, containing air, being heat- 

 ed, more air is expelled than if the bottle had been dry. 

 Both granted. — Now for the explication. The fpecific gra-> 

 vity of aqueous vapour has been found by De SaulTure, Watt, 

 and others, to be about -J or | of that of atmofpheric air in 

 like circumflances ; by fome experiments of my own I am 

 induced to think it is nearly .7, that of air being 1. Let the 

 temperature be 64-**, and the air be filled with vapour as much 

 as poffible in the temperature, in which cafe -~^ of the elaftic 

 force will be due to the vapour. (See Manch. Mem, Vol. V, 

 P. 2, page 559); then, by the theorem fo elaborately exem- 

 plified in Mr. G.*s former letters, we have — ^ = 



49.7 



~- zz .994, for the fpecific gravity of common air filled with 



^^'apour at 64*^, when that of dry air of the fame temperature 

 rwould be 1 . Thus it appears that my hypothefis not only ex- 

 plains the fa<5l of diminifiied fpecific gravity, but accounts for 

 the quantity of diminution. Can Mr. G. s theory of chemical 

 folution do this ? 



In the fecond cafe we find heat generating vapour, which 

 increafing in quantity and force with the temperature, diffufes 

 itfelf through the air in the bottle ; the hand being occafionally 

 removed from the mouth, fufl^ered the extra-portion of air 

 and vapour to ftart out ; juft as if there had been a generation 

 of a like portion of oxigen, or any other permanent gas, in- 

 ilead of the vapour ; in which cafe a portion of both does 

 certainly efcape. Mr. G. finds the vapour generated this 

 way between 59 and 126°, to be rather lefs than -g. of at- 

 VoL. IX.— December, 1804. T mofpheric 



