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Hydrochloric Acid

sulphuric, pure, gravity and specific

HYDROCHLORIC ACID (Formula, HCI; molecule weight, 36.5; synonyms, chlorhydric acid, hydrogen chloride, muriatic acid, spirits of acid is found in nature among the gases emanating from the active volcanoes, and occasionally in the spring and river waters which take their rise in volcanic districts, especially in South America. It is produced artificially by warming together common salt and strong sulphuric acid : Common salt. Sulphuric acid. Hydro sodium sulphate. Hydrochloric acid.

2NaC1 + - + 2HC1 the sodium of the common salt changing place with the hydrogen of the sulphuric acid. The hydrochloric acid escapes as a colorless gas with a most irritating acrid odor. It is very soluble in water, and in this form it is sold as " spirits of salts," hydrochloric acid, or muriatic acid. The most concentrated solution has a specific gravity of 15 deg. C. of 1.214 and contains 143.09 per cent. of the gas.

The solution commonly sold is, however, weaker, having a specific gravity of from 1.12 to 1.15, and contains about 24 or 3o per cent. of real acid.

Specific gravity Percentage of pure Specific gravity Percentage of pure at 15 deg. C. hydrochloric acid. at 15 deg. C. hydrochloric acid.

1.0103 2.22 1.1504 29.72 1.0189 3.80 1.1588 31.50

1.0310 6.26 1.1730 34.24 1.0557 11.02 36.63 1.0751 15.20 1.1938 38.67 1.0942 18.67 1.2021 40.51 1.1048 20.91 1.2074 1.1196 23.72 1.2124 1.1308 25.96 Hydrochloric acid becomes weaker by heating, as it rapidly volatilizes at boiling point of water. The pure acid should be quite colorless and free from perchloride of iron or organic matter. Free chlorine and sulphuric acid are also sometimes present. Chlorine may be detected by adding a drop or two of the solution to a mixture of starch paste and potassium iodide; if present, a blue color will be obtained. Absence of sulphuric acid may be proved by diluting the hydrochloric acid with six times its volume of water, and adding barium nitrate, no precipitate should be formed.

For photographic purposes this acid should be used as pure as possible. It must be preserved in closely stoppered bottles, kept covered from too strong light, because light decom poses it, and gives free chlorine. It is used in photography for dissolving out ferric oxalate from platinotype, bromide prints, etc., acting as a clearing solution. It is also used in the preparation of various chlorides.