OK THE DOCTRINE OF MIXED GASES. Ql 



Mr. Gough next wants a rigorous proof of the propofition. Impediments af- 

 that one gas affords an impediment to the motion of another, [^''^^^ diffUfiol" 

 but that two fuch fluids finally overcome their mutual ob- of another, 

 ftrudlions, and occupy the fame fpace in a fUte of perfect 

 independence. No one acquainted with the experimental 

 part of pneumatic chemi^ry would have required proofs of 

 fuch fads, becaufe he daily experiences them. Take two 

 phials filled with different gafes ; apply the mouth of one to 

 that of the other for a few moments ; upon withdrawing it, 

 the two phials will be found to have interchapged verv little 

 of their contents. This is a mpft unqueftionable prQof that 

 gafes afford impediment to each other's motion ; for, into a 

 perfed vacuum the air ruflies inllantaneoufly. Again, let 

 the phials remain in connexion for a few minutes, or at 

 moff, hours, and they will be found to have both gafes in 

 the fame proportion ; and this ftaie will continue in perpe- 

 tuity afterwards. That they are ultimately independent on 

 each other, is fufficiently marked by the circumftance, that 

 any fubftance having an affinity for one of them will with- 

 draw it from the mixture, if it will take it alone. 



Mr. Gough proceeds to give a neiv thtori/ of mixed gafes : Mr. Gough'* 

 At the commencement of this contro-verfy he came forth to "^^ theory of 

 defend the all-fufficiency of the old dodtrine of the chemical 

 union of water and air, and the homogenity of the atmo- 

 fphere, and to attack the new do61rine, which profcribes 

 chemical union in thefe inftances, and places for its funda- 

 mental and diftinguifbing maxim, that " mixed gafes iipK/'^^ . 

 ther attract nor repel one another :" It was therefore with 

 no fmall furprife that I found, upon his advances, that a 

 new theori) was Hill requifite ; but this furprife became afto- 

 nifliment, when I found the preamble admitted the exigence 

 of certain, " gafes that neither attract nor repel each other/* 

 The only clear information I could obtain from this fudden 

 revolution was, that Mr. Gough ufes the terms theory and 

 hypotliefm in a contrary fenfe to what philofophers in general 

 do. When I brought my hypotltefis (as he calls it) forward, 

 it was fupported by an extenfive train of facts, the refult of 

 long and careful inveftigation, none of which, that I know 

 of, has fince been controverted ; I mean what Mr. Gough 

 alludes to as a " number of probabilities of an experimental 

 nature:" Whereas Mr. Cough's theory is propofed without 



a fmgle 



