WATER. 43 



than spring-waters, but they soon throw off their hetero- 

 geneous matter, and become sweet, and purer than before, 

 and continue so for a long time. On this account it is 

 that the Thames water is generally preferred for long 

 voyages. 



Spring-water is impregnated with a portion of neutral 

 salts, which makes it hard ; it is also occasionally im- 

 pregnated with iron. It is, however, preferred as a be- 

 verage, for its coolness and pleasantness, though it is less 

 wholesome than good river-water. Springs are formed 

 by the intervention of clay and sand strata, the former 

 holding water, and the latter allowing it a free passage ; 

 so that no water is found, in digging wells, until clay is 

 penetrated. Springs of fresh water are found to exist 

 even under the sea. It is said that thirty have been dis- 

 covered under the sea on the south of the Persian Gulf. 

 St. Winifred's Well, in Flintshire, is said to throw up 120 

 tons of water in a minute, and to turn eleven mills in the 

 space of about a mile and a half. There are hot springs 

 in various parts of the world, of which the Great Geyser, 

 in Iceland, is the most remarkable. The chief hot-springs 

 in England are those of Bath and Bristol : the hot baths 

 of Bath are as high as 115 of Fahrenheit. 



The specific gravity of water is constantly changing 

 with the temperature of the atmosphere. At a mean rate, 

 it is 820 times heavier than air ; so that a cubic foot of 

 water will weigh 100O ounces avoirdupois very nearly. 



Water is of a very volatile nature, and soon raised to 

 vapour. If exposed to the action of the fire in an open 

 vessel, it would entirely go off in vapour, and conse- 

 quently occupy a space infinitely greater than it did be- 

 fore.* The expansive force which water acquires when 

 converted into steam is greater than that of gunpowder :f 

 thus a pound of water,converted into steam, may be made 

 to displace or raise a greater weight than a pound of 

 gunpowder would. It is to this principle that the mighty 



* According to Count Rumford, steam at 212 is 3000 times rarer 

 than water ; but with a great heat, it may be made to occupy more 

 than 10,000 times the space of water. 



f This is strikingly evident in Perkins's steam-gun, which will dis- 

 charge seventy halls in four seconds. 



