278 ELASTIC i'LUJDS, 



It is in a great meafure free from the inconvenience which 

 A. F. has attributed to it, (p. 168) and that the " fmall 

 fliaded circle" is not a " perforation," but a weight attached 

 to the counterpoife, 



I an), Sir, 



Your very obedient Servant, 



THOMAS YOUNG. 

 Welhec Street, 

 March 15, 180C. 



II. 



Mixed elaftic 

 fluids of dif- 

 ferent denfities 

 do not feparate 



but will they 

 mix without 

 agitation. 



Dr. Frieftley 

 thinks not. 



On the Tendtncij of Elaftic Fluids to Diffufion through each 

 other. By John Dalton *. 



In an early period of pneumatic chemiftry it was difcovered 

 that elaftic fluids of different fpecific gravities being ojice dif- 

 , fufed through each other, do not of themfelves feparate, by 

 long ftanding, in fuch manner as that the heavieft is found 

 in the lowefl place; but on the contrary, remain in a ftate of 

 uniform and equal diffufion. 



I)r. Frieftley has given us a feflion on this fubje6l (vid. 

 Experiments and Obfervations, &c. abridged. Vol. II. p. 441) 

 in which he has proved the facl above-mentioned in a fatis- 

 fadory manner; and everyone's experience fince, as far as 

 I know% has coincided with his conclufions. He has not 

 offered any conjedure concerning the caufe of this deviation 

 from the law obferved by inelaftic fluids ; but he fuggefls that 

 " if two kinds of air of very dififerent fpecific gravities, were 

 put into the fame veffel, with very great care, without the 

 leaft agitation that might mix or blend them together, they 

 might continue feparate, as with the fame care tuine and walet 

 may be made to do," 



The determination of (his point, which feems at firft view 

 but a trivial one, is of confiderable importance; as from it 

 we may obtain a flriking trait, either of the agreement or 

 difagreement of elaftic and jnelafiie fluids in their mutual 

 a6lion on each other. ' 



* Manchefter Memoirs, Vol. I. New Series-, 



It 



