Mineral Waters. 261 



heat of the water, which must be ascertained by 

 a good thermometer. There are many springs 

 that have a temperature of heat a little above the 

 middle temperature of the atmosphere: this 

 should be attended to, though they may not 

 seem to derive any particular qualities from that 

 superiority of heat. The middle temperature of 

 these springs is found to be about forty-eight : 

 they vary, however, in this respect according to 

 their height, as the temperature of hills and 

 mountains is found to differ according to their 

 elevation above the sea. The temperature of 

 these waters in high lands is lower than in the 

 less elevated. The degree of heat in the last is 

 from forty-eight to fifty ; of those that are higher 

 it is not so much. It may also be proper to com- 

 pare the temperature of these mineral springs 

 with that of some common springs in the neigh- 

 bourhood. 



The gaseous matters are separated from water 

 by boiling it in a retort, communicating by a 

 glass tube with a receiver immersed in a tub of 

 mercury. The most common of these is car- 

 bonic acid gas. Mr. Cavendish has shown that 

 water dissolves a quantity of it equal to itself in 

 bulk : but this is soon expelled from it again if 

 the water is agitated. Those who have not a 

 pneumatic apparatus, as it is called, that is, a. 

 tub or trough of quicksilver, with tubes and re- 

 ceivers, &c., may determine how much of this 

 gas any water contains by the following method. 



