Hydrogen chloride is very soluble in water. When 1 kgm. of water is saturated with the gas at 15° it increases in weight to 1.75 kgm., and the density is 1.231. It contains about 43 per cent, of HCl; the commercial acid contains about 39 per cent., its density being 1.20.
Densities of aqueous solutions of hydrochloric acid at 15°.
| Density | Per cent. HCl | | 1.0491 | 10 | | 1.0784 | 15.84 | | 1.1014 | 20.29 | | 1.1271 | 25.18 | | 1.1490 | 29.35 | | 1.1696 | 33.39 | | 1.1901 | 37.23 | | 1.2002 | 39.15 |
Expt. 17. - The great solubility of hydrochloric acid gas in water may be demonstrated by the fountain experiment. A large round-bottomed flask is filled with the gas by displacement (this takes some time) and fitted with a rubber stopper carrying a tube drawn out inside the flask into a jet. The flask is inverted with the tube dipping into water coloured with blue litmus contained in a second large flask, as shown in.  | Fig: Demonstration of the solubility of hydrogen chloride |
By blowing into the short tube on the second flask a drop of water is forced into the upper flask. The gas is instantly dissolved, the atmospheric pressure forces the water in the lower flask in the form of a fountain into the upper flask, and the litmus is turned red by the acid solution formed.
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