HYDROCHLORIC ACID. 



363 



the retort, hydrochloric acid gas comes off and is condensed in 

 the receiver, affording an aqueous solution of the acid, of sp. 

 gr. 1.170, and which contains about 37 per cent of dry acid; 

 while a mixture of sulphate and bisulphate of soda remains in the 

 retort. Supposing single equivalents of oil of vitriol and chlo- 

 ride of sodium to be employed, to which the preceding propor- 

 tions approximate, then the rationale of the action is as fol- 

 lows : 



Process for hydrochloric acid : 



Before decomposition. 



733 Chloride of f Chlorine, 

 sodium 1 Sodium. 



f Hydrogen. 

 Oil of vitr. j Oxygen. . 



LSulphu. acid 501 



13464 



After decomposition. 

 4544 hydroc. acid 



892 sulph. of soda 



13464 



13464 



Or in symbols ; NaCl and HO,SO 3 = HC1 and NaO,SO 3 . 



This process is more economically conducted on the large 

 scale in a cast iron cylinder, about 5 feet in length and 2j 

 in diameter, laid upon its side, which has moveable ends, gene- 

 rally composed of a thin paving stone cut into a circular disc 

 and divided into two unequal segments. A charge of three or 

 four cwt. of salt is introduced into the retort, and after the bot- 

 tom is heated, undiluted oil of vitriol is added in a gradual man- 

 ner by means of a long funnel, and in proportion not exceeding 

 the equivalent for the chloride of sodium. In such circumstances, 

 the lower part of the cylinder exposed to the sulphuric acid is 

 not much acted upon, while the roof of the cylinder is pro- 

 tected from the hydrochloric acid fumes by a coating of fire-clay 

 or thin split bricks. The hydrochloric acid gas is conducted by 

 a strong glass tube into a series of large jars of salt-glaze ware, 

 connected with each other like Wolfe's bottles, and containing 

 water in which the acid condenses. 



Properties. Hydrochloric acid is obtained in the state of gas 

 by boiling an ounce or two of the fuming aqueous solution, in a 

 small retort, or by pouring oil of vitriol upon a small quantity 

 of salt in a retort, and is collected over mercury It is an in- 

 visible gas, of a pungent acid odour, and produces white fumes 



