This acid is formed by acting upon common salt (which is chloride of sodium) by concentrated sulphuric acid.

The water of the acid is decomposed, and its hydrogen combines with the chloride of the salt to form muriatic acid, and this unites with the sulphuric acid to form sulphate of soda; 60 parts of common salt and 49 parts of concentrated sulphuric acid, afford, by this mutual action, 37 parts of muriatic acid and 72 parts of sulphate of soda.

The muriatic acid of commerce has usually a yellowish tinge, but when chemically pure it is colorless.

The former is commonly contaminated with sulphurous acid, sulphuric acid, chlorine, iron, and sometimes with arsenic.
Muriatic acid, from the fact of the presence of the chlorine, is used in the Daguerreotype process for dissolving gold, and in combination with various accelerators.

Its presence can be detected by ammonia.