HYDROCHLORIC ACID. 



365 



HYDROCHLORIC ACID. 



It thus appears that the strongest hydrochloric acid that can 

 be easily formed contains six atoms of water ; this liquid allows 

 acid to escape when evaporated in air, and comes according to 

 an observation of my own, to contain 1 2 atoms of water to I 

 of acid. Distilled in a retort, it was found, by Dr. Dalton, to 

 lose more acid than water till it attained the specific gravity 

 1 .094, when its boiling point attained a maximum 230, and the 

 acid then distilled over unchanged. Dr. Clark finds by careful 

 experiments that the acid which is unalterable by distillation, 

 contains 16.4 equivalents of water. 



The concentrated acid is a colourless liquid, fuming strongly 

 in air, highly acid, but less corrosive than sulphuric acid ; not 

 poisonous when diluted. It is decomposed by substances which 

 yield oxygen readily, such as metallic peroxides and nitric acid, 

 which cause an evolution of chlorine, by oxidating the hydrogen 

 of the hydrochloric acid. A mixture of 1 measure of nitric 

 and 2 measures of muriatic acid forms aqua regia, which dis- 

 solves the less oxidable metals, such as gold and platinum, 

 through the agency of the disengaged chlorine. 



The hydrochloric acid of commerce has a yellow or straw 

 colour, which is generally due to a little iron, but may be oc- 

 casionally produced by organic matter, as it is sometimes des- 

 troyed by light. This acid is rarely free from sulphuric acid, 

 the presence of which is detected by the appearance of a white 

 precipitate of sulphate of barytes, on the addition of chloride 

 of barium to the hydrochloric acid diluted with 4 or 5 times its 

 bulk of distilled water. Sulphurous acid is also occasionally 

 present in commercial hydrochloric acid, and is indicated by 

 the addition of a few crystals of protochloride of tin, which salt 



