Water in tie State of Vapour. [BookVIL 



of water, in that degree which conftitutes fleam, rati- 

 fies them fo exceedingly, as to occafion them to occupy 

 a fpace fome hundred times greater than the original 

 bulk of the fluid, and it is that alfo which volatilizes 

 and enables them to afcend through the air, and to 

 overcome its refiftance. 



But when fleam is expofed to a flill greater degree 

 of heat, its volume is augmented ftill more confider- 

 ably. That heat which makes water boil, and which 

 rarifies it only one twenty- fixth, rarirks its vapour to 

 eighteen hundred times the bulk of the water which 

 produced it. This may be very readily demonilrated, 

 by taking a glafs tube, at one end of which is a bulb 

 of two inches in diameter, and dropping into it a fin 

 gle drop of water, the diameter of wiiich we will fup- 

 pofe to be one-tenth of an inch. The fquares of thefe 

 two fpheres, with regard to each other, will be as 1800 

 are to one. Upon heating the buib of the tube over 

 the frame of a fpirit lamp, the air will firft be expelled, 

 and afterwards the drop of water will be converted into 

 fteam, and take poiTelTUm of the whole of the bulb ; 

 as may be proved by plunging the mouth of the tube 

 imo cold water, and furTering the fleam within the 

 bulb to return to its fluid (late. In this cafe, the 

 preflure of the atmofpliere will caufe the \vatc?r to rum 

 into the tube, and to occupy that {pace within the 

 bulb, which before was occupied by the vapour, and 

 thus the fact \viii be afcertained. 



If, however, any obftacle is oppofed to the expanfive 

 force of fleam, the heat augments its refiilance in a 

 degree proportionate to the augmentation of its vo- 

 lume. The power of refiftance afforded by the va- 

 pour of water is prodigious, and has of late years been 

 made fubfervient to fome mechanical purpofes of the 

 greateft importance. Mufchenbroek has proved by 



experiment, 



