442 PRINCIPLES OF CHEMISTRY 



I 



is accomplished were hermetically closed, and only presented one outlet, 

 then the escape of the hydrochloric acid would only proceed through 

 the escape pipe intended for this purpose. But as it is impossible to 

 construct a perfectly hermetically closed furnace, it is necessary to 

 increase the draught by artificial means, or to oblige the hydrochloric 

 acid gas to pass through those arrangements in which it is condensed. 

 This is done by connecting the ends of the tubes through which the 

 hydrochloric acid gas escapes from the furnace with high chimneys, where 

 the strong draught proceeding from the combustion of the fuel carries 

 off the hydrochloric acid and air which is mixed with it. This causes a 

 current of hydrochloric acid gas to pass through the absorbing apparatus 

 in a definite direction. Here it encounters a current of water flowing 

 in the opposite direction, by which it is absorbed. It is not cus- 

 tomary to cause the acid to pass through the water, but only to bring 

 it into contact with the surface of the water. The absorption apparatus 

 consists of large earthenware vessels having four orifices, two above and 

 two lateral ones in the wide central portion of each vessel. The upper 

 orifices serve for connecting the vessels together, and the hydrochloric 

 acid gas escaping from the furnace passes through these tubes. The 

 water for absorbing the acid enters at the upper, and flows out from the 

 lower, vessel, and passes 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 absorption of the hydro- 

 chloric acid is carried on in the so-called coke towers. These are high 

 chimneys, like that shown in fig. 66. They are frequently divided into 

 two portions, or consist of two adjacent chimneys. A lattice work of 

 bricks, C, is laid 011 the bottom of these towers, on which coke is 

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

 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 



solutions of composition HoO + ;jHCl when boiled (the residue will be almost HC1,HH.X)) 

 evolve (not water but) a solution of the composition HoO + 445/i*HCl ; for example, <>n dis- 

 tilling HCl,10HoO, HCl,28HoO is first obtained in the distillate. As the strength of the 

 residue becomes greater, so also does that of the distillate, and therefore in order to com- 

 pletely absorb hydrochloric acid it is necessary in the end to have recourse to \vuter. 



As in Russia the manufacture of sodium sulphate from sodium chloride lias not yet 

 been sufficiently developed, and as hydrochloric acid is required for many technical pur- 

 poses (for instance, for the preparation of zinc 'chloride, which is employed for soaking 

 railway sleepers), therefore the salt is often treated mainly for the manufacture of hydro- 

 chloric acid. 



