SODIUM" CHLORIDE BEKTHOLLET'S LAWS 451 



flows out from the lower, vessel, passing through the lateral orifices 

 in the vessels. The water flows from the chimney towards the furnace 

 and it is therefore evident that the outflowing water will be the most 

 saturated with acid, of which it actually contains about 20 per cent. 

 The absorption in these vessels is not complete. The ultimate absorp- 

 tion of the hydrochloric acid is carried on in the so-called coke towers^ 

 which usually consist of two adjacent chimneys. A lattice- work of 

 bricks is laid on the bottom of these towers, on which coke itf 

 piled up to the top of the tower. Water, distributing itself over th$ 

 coke, trickles down to the bottom of the tower, and in so doing absorbs 

 the hydrochloric acid gas rising upwards. 



It will be readily understood that hydrochloric acid may be 

 obtained from all other metallic chlorides. 33 It is frequently formed 

 in other reactions, many of which we shall meet with in the further 

 course of this work. It is, for instance, formed by the action of 

 water on sulphur chloride, phosphorus chloride, antimony chloride, &c. 



Hydrochloric acid is a colourless gas having a pungent suffocating 

 odour and an acid taste. This gas fumes in air and attracts moisture, 

 because it forms vapour containing a compound of hydrochloric acid and 

 Water. Hydrochloric acid is liquefied by cold, and under a pressure of 

 40 atmospheres, into a colourless liquid of sp. gr. 0'908 at 0, 34 boiling 

 point 35 and absolute boiling point + 52. We have already seen 

 (Chapter I.) that hydrochloric acid combines very energetically with' 

 water, and in so doing evolves a considerable amount of heat. The 

 solution saturated in the cold attains a density 1'23. On heating such, 

 a solution containing about 45 parts of acid per 100 parts, the hydro- 



33 Thus the metallic chlorides, which are decomposed to a greater or less degree by 

 water, correspond with feeble bases. Such are, for example, MgCls, AlClj, SbClj, BiClj. 

 The decomposition of magnesium chloride (and also carnallite) by sulphuric acid pro- 

 ceeds at the ordinary temperature; water decomposes MgCLj to the extent of 50 p.c. 

 when aided by heat, and may be employed as a convenient method for the production 

 of hydrochloric acid. Hydrochloric acid is also produced by the ignition of certain 

 metallic chlorides in a stream of hydrogen, especially of those metals which are easily, 

 reduced and difficultly oxidised for instance, silver chloride. Lead chloride, when 

 heated to redness in a current of steam, gives hydrochloric acid and lead oxide. The 

 multitude of the cases of formation of hydrochloric acid are understood from the 

 fact that it is a substance which is comparatively very stable, resembling water in this 

 respect,,and even most probably more stable than water, because, at a high temperature 

 and even under the action of ligbt, chlorine decomposes* water, with the formation of 

 hydrochloric acid. The combination of chlorine and hydrogen also proceeds by their 

 direct action, as we shall afterwards describe. 



5* According to Ansdell (1880) the sp. gr. of liquid hydrochloric acid at = 0'908, at 

 11-67 = 0-854, at 22'7 = 0'808, at 83 = 0'748. Hence it is seen that the expansion of this 

 liquid is greater than that of gases (Chapter II., Note 34). 



