Hydrochloric Acid, Solution of

The hydrochloric acid of commerce is a solution of the above gas in water. When exposed to the air it emits grey fumes. Water at 40° F. absorbs about 480 times its bulk of hydrochloric acid, increasing in volume about one third in doing so, acquiring a density of 1·2109, and then containing nearly forty-three per cent. of the acid. Strength of Solution of Hydrochloric Acid, 77° Fahr. ( E. Davy. ) | Sp. Gravity. | Hydrochloric acid in 100 parts. | Sp. Gravity. | Hydrochloric acid in 100 parts. | | 1·21 | 42·43 | 1·10 | 20·20 | | 1·20 | 40·40 | 1·09 | 18·18 | | 1·19 | 38·38 | 1·08 | 16·16 | | 1·18 | 36·36 | 1·07 | 14·14 | | 1·17 | 34·34 | 1·06 | 12·12 | | 1·16 | 32·32 | 1·05 | 10·10 | | 1·15 | 30·30 | 1·04 | 8·08 | | 1·14 | 28·28 | 1·03 | 6·06 | | 1·13 | 26·26 | 1·02 | 4·04 | | 1·12 | 24·24 | 1·01 | 2·02 | | 1·11 | 22·22 | In the laboratory, solution of hydrochloric acid is in constant use. It may be easily prepared from chloride of sodium and sulphuric acid. The retort should be connected with a couple of Woulfe’s bottles; into the first of which a small quantity of water should be poured, to detain any impurities mechanically carried over with the gas; the second bottle should contain four parts of water, and should be placed in a ve el of cold water, as the gas in becoming condensed, disengages a large amount of heat. The gas comes off and is absorbed readily by the water upon applying a gentle heat to the retort. It is by this last method that solution of hydrochloric acid is obtained in such enormous quantities [347] for the various purposes in which it is used, in the arts and manufactures. [347] In South Lancashire alone, more than 1000 tons of hydrochloric acid in solution are made weekly. Hydrochloric acid is, in fact, a by-product in the manufacture of carbonate of soda, and is generated during the first stage of the operation, known as the salt-cake proce , which consists in the decomposition of salt by sulphuric acid, and is accomplished in a furnace called the salt-cake furnace. The hydrochloric acid gas which is given off escapes from the furnace through a flue with the products of combustion into high brick towers filled with coke or stones, over which a stream of water trickles down, the whole of the acid vapours are thus condensed, the smoke pa ing off by a chimney connected with the towers. The diluted acid solution thus formed is concentrated by the aid of the apparatus shown in section in figs. 1, 2, and 3. This apparatus consists of several cast-iron cylinders, 57 feet long by 27 feet in diameter, closed in the same manner as gas retorts, by lids luted with clay. One of the lids has an opening o , into which is fitted the stoneware or leaden pipe a , conveying the hydrochloric acid to the condensing apparatus. The other, or posterior lid, is also provided with an opening d , through which is pa ed the tube of a leaden funnel, so that after the retort is filled with salt sulphuric acid may be poured in. The construction of the furnace in which two retorts are usually placed, permits the flame of the fire at O to play round the cylinders before reaching the flue leading to the chimney F. B is an arch over the furnace. The first stage of the operation consists in filling each cylinder with 330 lbs. of salt. The lids or covers are then luted on, and the fire is kindled. The requisite quantity of strong sulphuric acid is next poured into the retort, and the funnel having been withdrawn from D, the hole is covered by a clay plug. IMG:596405606043057898_i864.png: Fig. 1. As soon as the reaction is over, the 396 lbs. of sulphate of soda produced are removed, and the operation repeated. The condensation apparatus 1 and 3 is composed of rows of Woulfe’s bottles, partly filled with water, care being taken to place the first pairs of these bottles in a tank of cold water. The condensation of the last portions of hydrochloric acid gas is effected either by the aid of the coke columns, or in leaden chambers, into which fine jets of cold water are injected on all sides. “A saturated solution of hydrochloric acid in water has the specific gravity of 1·21; and when heated in a retort, loses at first hydrochloric acid gas, but after a time an aqueous acid distils over, at the ordinary atmospheric pre ure, containing 20·22 per cent. of hydrochloric acid, and boiling constantly at 110° C. If the distillation be conducted under diminished pre ure, the liquid boils at a lower temperature, and attains a composition which is different for each boiling point; hence the dilute acids thus obtained by boiling the solution of hydrochloric acid gas in water, cannot be considered as definite compounds of hydrochloric acid and water.” [348] [348] Roscoe and Dittmar. IMG:596405606043057898_i865-1.png: Fig. 2. IMG:596405606043057898_i865-2.png: Fig. 3. Commercial hydrochloric acid is usually of a yellow colour owing to its being contaminated with iron. It also very frequently contains sodium, arsenic, sulphuric and sulphurous acids, and free chlorine. Pure aqueous solution of hydrochloric acid should leave no residue upon evaporation; it should give no precipitation of ferric oxide when saturated with ammonia, sulphuretted hydrogen should cause no turbidity in it; if diluted with three or four times its volume of water, and chloride of barium be added, no white cloud or precipitate should form in the mixture; nor should the acid, if pure, discolour a fluid made faintly blue with iodide of starch. Hydrochloric acid is largely consumed in the manufacture of chlorine, sal ammoniac, chloride antimony, glue, phosphorus, in the preparation of carbonic acid for the manufacture of artificial mineral waters, in beet-root sugar works, hydro-metallurgy, and alone, or mixed with nitric acid, for di olving various metals. [349] See Acids , Effects of Vegetation on , Chlorine . [349] Wagner.