154- Chemistry. [Lecture 29. 



snow water : the place where it is really found is 

 in the bowels of the earth, and in mineral waters ; 

 but in very small quantities. It is found com- 

 pounded with other substances, as ores of metals, 

 gypsum, &c. Its uses are in pharmaceutical opera- 

 tions, dying, bleaching, hat-making, &c. Brewers 

 also find it the most effectual means of cleansing 

 their foul casks. It is common to see them burn 

 a small quantity of brimstone in their empty 

 casks, which fills them with sulphurous acid 

 gas, and thus effects the purpose. 



The nitric and muriatic acids are so named 

 from the two salts, nitre (nitrat of potass) and 

 common salt (muriat of soda), from which they 

 are always prepared. In their strongest state 

 they are not so heavy as the sulphuric acid, 

 therefore are said to contain more water and less 

 salt. They are more fixed than water, requiring 

 a little more heat to convert them into vapour. 

 Yet we have reason to think that the saline sub- 

 stances of which they are composed are very vo- 

 latile, but they seem depressed by the water; 

 and it is remarkable that a strong acid is more 

 fixed than water, though composed of water, 

 and a salt more volatile than that fluid. If heat 

 is applied to these acids, they fly off in elastic 

 vapour, which it is impossible to condense, any 

 luting, or even the vessels themselves, being busst 

 by it. If, however, we throw a small quantity of 

 water into the receiver, the vapours are immedi- 

 ately absorbed by the water ; yet if we continue 



