WATER. 41 



has been already alluded to, is, that a column of air, of 

 the whole height of the atmosphere, will balance a column 

 of quicksilver of from 28 to 31 inches, according to the 

 state of the air. When the atmosphere is loaded with 

 aqueous vapour, it becomes lighter, aqueous vapour be- 

 ing considerably lighter than atmospheric air ; conse- 

 quently it will not balance so large a quantity of quick- 

 silver, and the quicksilver of course sinks. When the 

 aqueous vapour is condensed into rain, and yields its 

 place to the common atmospheric air, the quicksilver 

 again rises. Barometers are made in different ways, but 

 the principle is invariably the same. Barometers are 

 used to ascertain the height of mountains or other ele- 

 vated situations, the mercury sinking one-tenth of an inch 

 at about every hundred feet of ascent. 



WATER. 



Water a compound body Different states of water Water universally diffused 

 Salt-water Snow-water Rain-water River-water Spring-water Ex- 

 pansive power of water converted into steam Theory of boiling, &c. 4c. 



WATER is a clear colourless liquid, and if pure, is 

 without either taste or smell. It used to be imagined 

 by the ancients that water was an element or simple body; 

 but it is now well known to be a compound of two gases, 

 oxygen and hydrogen, in the proportion of about So parts 

 of the former to 15 of the latter by weight.* 



Water exists in four distinct states : in Ice, Water, 

 Vapour, and in combination with other bodies. Ice is the 

 simplest state of water, it being water deprived of the 

 greatest portion of its caloric. When water receives an 

 excess of caloric, it becomes vapour or steam. 



Water is most universally diffused, for there is scarcely 

 any body in nature that does not contain it : wherever 

 there is matter there appears to be water. Hartshorn 

 kept^/y years, so as to be as dry and hard as any metal, 

 and even capable of producing sparks like steel when 

 struck with a flint, will, if distilled, produce one-eighth of 



* Water contains air holding a larger quantity of oxygen than atmos- 

 pheric air ; fishes breathe this air, which if deprived of they die. 



