462 PRINCIPLES OF CHEMISTRY 



with hydrochloric acid or a mixture of common salt and sulphuric 

 acid 4 and washing the gas with water to remove hydrochloric acid.* 

 Chlorine cannot be collected over mercury, because it combines with 

 it as with many other metals, and it is soluble in water j however, it 

 is but slightly soluble in hot water or brine. Owing to its great 

 weight, chlorine may be directly collected in a dry vessel by carrying 

 the gas-conducting tube down to the bottom of the vessel. The chlorine 

 will lie in a heavy layer at the bottom of the vessel, displace the air, 

 and the extent to which it fills the vessel may be followed by its colour. 



not participate in any way in the reaction, is added to the mixture to prevent its fusing. 

 The reactions may be expressed by the following equations: (1) 8MgCl 2 + 8MnCl 2 + 8O 

 <= Mg 3 Mn 3 O 8 + 12C1 ; (2) Mg 3 Mn 5 O d + 16HC1 = 8MgCl a + SMnCL, + 8H 2 O + 4C1. As nitric 

 acid is able to take up the hydrogen from hydrochloric acid, a heated mixture of these 

 acids is also employed for the preparation of chlorine. The resultant mixture of chlorine 

 and lower oxides of nitrogen is mixed with air and steam which regenerates the HNO 3 , 

 while the chlorine remains as a gas together with nitrogen, in which form it is quite 

 capable of bleaching, forming chloride of lime, &c Besides these, Solvay and Mond's 

 methods of preparing chlorine must be mentioned. The first is based upon the reaction 

 CaCl 2 +SiO i + O(air) = CaOSiO i + C1 2 , the second on the action of the oxygen of the air 

 (heated) upon MgCl 2 (and certain similar chlorides) MgCl 2 -t- O = MgO + C1 2 . The remaining 

 MgO is treated with sal-ammoniac to re-form MgCl 2 (MgO + 2NH 4 C1 = MgCl 2 + H 2 + 2NH 3 ) 

 and the resultant NH 3 again converted into sal-ammoniac, so that hydrochloric acid 

 is the only substance consumed The latter processes have not yet found much appli- 

 cation. 



4 The following proportions are accordingly taken by weight : 6 parts of powdered man- 

 ganese peroxide, 11 parts of salt (best fused, to prevent its frothing), and 14 parts of sul- 

 ph. uric acid previously mixed with an equal volume of water The mixture is heated in a 

 salt bath, so as to obtain a temperature above 100 The corks in the apparatus must 

 be soaked in paraffin (otherwise they are corroded by the chlorine), and black india-rubber 

 tubing smeared with vaseline must be used, and not vulcanised rubber (which contains 

 sulphur, and becomes brittle under the action of the chlorine). 



The reaction which proceeds may be expressed thus. MnO 2 + 2NaCl + 2H 2 SO 4 

 = MnSO 4 + Na 2 SO 4 +2H 2 O + Cl.> The method of preparation of C1 2 from manganese 

 peroxide and hydrochloric acid waa discovered by Scheele, and from sodium chloride by 

 Berthollet. 



5 The reaction of hydrochloric acid upon bleaching powder gives chlorine without 

 the aid of heat, CaCl 2 O 2 + 4HCl = CaCLj-i-2H 2 O + 2Cl2, and is therefore also used for the 

 preparation of chlorine. This reaction is very violent if all the acid be added at once ; 

 it should be poured in drop by drop (Merme*, Kiimmerer). C. Winkler proposed to mix 

 bleaching powder with one quarter of burnt and powdered gypsum, and having damped 

 the mixture with water, to press and cut it up into cubes and dry at the ordinary 

 temperature. These cubes can be used for the preparation of chlorine in the same 

 apparatus as that used for the evolution of hydrogen and carbonic anhydride the 

 disengagement of the chlorine proceeds uniformly. 



A. mixture of potassium dichromate and hydrochloric acid evolves chlorine perfectly 

 free from oxygen (V. Meyer and Langer). 



6 Chlorine is manufactured on a large scale from manganese peroxide and hydrochloric 

 acid. It is most conveniently prepared in the apparatus shown in fig. 66, which con- 

 eists of a three-necked earthenware vessel whose central orifice is the largest. A clay 

 or lead funnel, furnished with a number of orifices, is placed in the central wide neck 

 of the vessel. Roughly-ground lumps of natural manganese peroxide are placed in the 

 funnel, which is then closed by the cover N, and luted with clay. One orifice is closed 



