ON- THE CONSTITUTION OF MIXED GASES, ^C. 259 



Having now ftated the chief principles which feem to be 

 efiabli filed from the following feries of fa6ls and obfervations, 

 I fliall proceed to treat of them under the feveral heads *. 



ESSAY II. 



On the Force of Steam or Vapour from Wattr arid various other 

 Liquids, both in a Vacuu7n and in Air. 



SECTION I. — On Vapour in Vacuo. 



THE term Jieam or vapour is equally applied to thofe elaflic Steam or vipoui 



fluids whichi by cold and preflure of certain known degrees, ^^^'^^'^: ^V* 



J J 1 II • • 1- • 1 n r, anelafticfluid 



are reduced wholly or in part into a liquid ftate. Such are capable of be- 



the elaftic fluids arifing from water, alkohol, ether, ammonia, coming liquid by 



o /^i in-n-ii 1 1 • cold and preffureo 



mercury, &c. Other elaltic fluids that cannot be reduced, (jafgsnot fy, 

 of rather that have not yet been reduced, into a liquid flate 

 by the united agency of thofe two powers, are commonly 

 denominated gafes. There can fcarcely be a doubt entertain- 

 ed refpeding the reducibility of all elaflic fluids of whatever 

 kind into liquids ; and we ought not to defpair of efl^efling 

 it in low temperatures and by ftrong preflure exerted upon 

 the unmixed gafes. However uneflential the diflindion be- 

 tween the gafes and vapours may be in a chemical fenfe, their 

 mechanical adion is very different. By increafing the quantity Remarl:abie d!f- 

 of any gas in a. given fpace the force of it is proportionally in- ^"^"" betweea 

 creafed ; but increafing the quantity of any liquid in a given fteam ^nd of 

 fpace does not at all aflc(fl the force of the vapour arifing from ^^' ^^ heat : 



.^, i,.i- r I • the former being 



It. On the other hand, by increafing the temperature o\ any prodigioufly 

 gas a proportionate increafe of elafticity enfues ; but when the greater, 

 temperature of a liquid is increafed, the force of vapour from 

 it is increafed with amazing rapidity, the increments of elaf- 

 ticity forming a kind of geometrical progreffion, to the arith- 

 metical increments of heat. — Thus, the ratio of the elaftic 

 force of atmofpheric air of 32* to that at 212®/ is nearly as 

 5:7; but the ratio of the force of aqueous vapour proceeding 

 from water of 32° and 212°, is as 1 : [50 nearly. 



The object of the prelent eflay is to determine the utmoft Objeft of th6' 

 force that certain vapours, as that from water, can exert at^"^^*"** ^^^ 

 different temperatures. The importance hitherto attached to 

 tkis enquiry has arifen chiefly from the confideration of fteanx 



* Here followed the elTay I. on mixed gafes. W. N. 



$9 M 



