ON THE CONSTITUTION OF MIXED GASES, SfC. 26) 



ftanced, water of any temperature may be poured into the 

 wide tube, and thus made to fiirround the upper part or 

 vacuum of the barometer, and the effect of temperature in 

 the produftion of vapour within can be obferved from tiie 

 depreffion of the mercurial cohimn. In this way I have had 

 water as high as 155° furrounding the vacuum; but as the 

 higher temperatures might endanger a glafs apparatus ; in^ 

 iiead.of it I uled the following: — 



Having procured a tin tube of four inches in diameter and The veffel con- , 

 two teet long, with a circular plate of the fame foldered tOj.pj.jJi ^g^^g^^^'g^ 

 one end having a round tube in the center like the tube of a of tin for tem- 

 refleding telelcope, I got another fmaller tube of the fame ^^;||'"'" "n^a 

 length foldered into the larger, fo as to be in the axis or centre iyphon barome- 

 ofit: the fmall tube was open at both ends, and on this con- ^" *^l"v ^'* 



' _ •" Ihew the de- 



flruclion water could be poured into the large veffel to lillpreffion. 

 it, whilft the central tube was expofed to its temperature. 

 Into this central tube I could infert the upper half of a fyphon 

 barometer, and fix it by a cork, the top of the narrow tube 

 alfo being corked ; thus (he effctfl of any temperature under 

 212" could be afcertained, the deprefiion of the mercurial 

 column being known by the afcent in the exterior leg of the 

 fvphon. 



The force of vapour fiorn water between 80° and 212° Another method 



,,-,,,.,, p . -, ,1 by obferving the 



may alio be determined by means ot an air-pump ; and the boil.ng point in 



refults exa6tly agree with thofe determined as above. Take the air pump, 

 a Florence flafk half filled with hot water, into which infejt of the barometer 

 the bulb of a thermometer ; then cover the whole with a gage. 

 receiver on one of the pump-plates, and place a barometer 

 gage on the other : the air being fiowly exhaufted, mark 

 both the thermometer and barometer at the moment ebulli- 

 tion commences, and the height of the barometer gage will 

 denote the force of vapour from water of the obferved tem- 

 perature. This method may alfo be ufed for other liquids. 

 It may be proper to obferve the various thermometers ufed 

 in thefe experiments were duly adjufted to a good ftandard 

 one. 



After repeated experiments by all thefe methods, and a Hence the force 

 careful comparifonof the refults, I was enabled to digeft the fj^l''"^^"^^'* 

 following table of thfj force of fleam from water in all the 

 temperatures from 32° to 212°. 



Two important enquiries ftill remained, the firft to deter- 

 n^ine the force of fleam from water above 212° and below 



4 32°; 



