SULPHUR. 213 



phial like oil. When quite free from all impurity, 

 its specific gravity (when as strong as possible) is 

 1*84/7 : if it be heavier than this, it is contami- 

 nated with lead. The liquid, in this state, is a 

 compound of 1 atom acid and 1 atom water. 

 Now 



1 atom acid = 5 

 1 atom water = l-li25 



6-125 



So that 6*125 parts of it contain 1*125 water and 

 5 of pure acid. Acid of this strength requires 

 the highest temperature to boil it. Mr. Dalton 

 states that its boiling temperature is 620 but 

 it is extremely difficult to determine such high 

 temperatures with accuracy. I have satisfied 

 myself, however, that the boiling point of this 

 acid is above 600. 



If to 6-125 parts of this acid we add 1*125 

 parts of water, so as to form a compound of 1 

 atom acid and 2 atoms water, we obtain a liquid 

 of the specific gravity of 1'78. Acid of this 

 strength possesses the remarkable property of 

 freezing at a higher temperature than acid 

 of any other strength its freezing point, ac- 

 cording to the experiments of Mr. Keir, being 

 45. Its boiling point, according to Mr. Dalton, 

 is 435. 



3. Protosulphate of iron is a salt composed 

 of 



O3 



