790 CHLORINE 



hydrogen merely by their presence or by contact, without themselves taking any 

 direct part in the process : the chemist is familiar with many similar examples of 

 catalytic action. For an elaborate discussion of the principles involved in Deacon's 

 new process we may refer to the ' Journal of the Chemical Society,' Sept. 1872. 



On the Industrial Manufacture of Chlorine, M. F. Lalande andM. Prud'homme have 

 the following remarks : 



The reaction of anhydrous sulphuric acid, mixed with air or oxygen, upon heated 

 alkaline chlorides, which has given rise to Deacon's patent for the preparation of 

 chlorine and of sulphate of soda, has led us to generalise this process. We have 

 chiefly experimented with silicic, boric, stannic, and phosphoric acids, and also with 

 alumina. When any of these bodies, silica, for instance, is mixed with an alkaline 

 chloride, or with an alkaline earth or earthy chloride, and over this mixture, while 

 being heated to red heat, a current of dry oxygen or air is passed, chlorine is 

 evolved, and a silicate formed of the base of the chloride employed : 



SiO 2 + NaCl + =SiO s NaO + Cl (SiO 2 + ZNTaCl + O =10 > a 2 8iO s + Cl"). 



At a red heat, therefore, oxygen expels chlorine, when there is simultaneously present 

 an acid capable of uniting with the base which is formed. Chlorides heated by them- 

 selves in a current of oxygen (chloride of calcium, for instance) do not give off chlorine. 

 When a current of hydrochloric add gas is passed, along with oxygen, over the mixture 

 of silica and chloride, the acid regenerates the chloride and decomposes the silicate : 



Si0 2 .NaO + HC1 = SiO 2 + NaCl + HO (KTa 2 SiO 3 + 2HC1 = SiO 2 + ZNaCl + H 2 ). 



In this way a continuous evolution of chlorine is obtained. Instead of taking the 

 mixture of chlorine and silica, the silicate of the metal in which the chlorine is 

 contained, or a mixture of silica and the oxide of that metal, is taken. Since analogous 

 reactions occur with the acids above mentioned, we may state that it is general. The 

 steam formed during the phase of reaction : 



Si0 2 .NaO + HC1 = SiO 2 + NaCl + HO 



gives rise to two secondary actions : 

 (1). The chlorine decomposes the water at red heat : 



HO + Cl = HC1 + (H 2 + Cl 2 = 2HC1 + O). 

 (2). The steam decomposes the chlorides at red heat : 



NaCl + HO = NaO + HC1 (2XaCl + H 2 O = KTa 2 O + 2HC1). 



It is probable that under these conditions an equilibrium exists between the 

 quantities of chlorine, aqueous vapour, and hydrochloric issuing from the apparatus, 

 or a limit of maximum between the quantity of chlorine produced and the hydrochloric 

 acid evolved and issuing from the apparatus. This limit of maximum will bo the 

 greater according as the temperature required for the reaction be less high. Some of 

 our experiments having been made by causing the substances operated with to be 

 imbibed with pumice-stone, wo have been induced to try whether pumice-stone alone 

 would yield any result, that material being a complex silicate and a substance 

 belonging to the category of those indicated by us. We have found that with 

 pumice-stone an evolution of chlorine is obtained comparable to that obtained from 

 the other substances, more particularly silica and lime, boric acid and lime, stannic 

 acid and lime, alumina and chloride of sodium ; since the same result is obtained 

 with lumps of brick, it might be ascribed to the porosity of these substances ; but 

 this opinion is gainsaid by the fact, that under the same conditions pipeclay, a silicate 

 of alumina and a very porous body, does not give rise to any appreciable reaction ; 

 it therefore appears possible that hydrochloric acid converts the surface of pumice- 

 stone into a mixture of silica and chlorides. We have compared the production of 

 chlorine in our experiments with that obtained by using bricks impregnated with 

 sulphate of copper (Deacon's patent) ; the quantity of chlorine obtained in both cases 

 is the same ; but with bricks impregnated with sulphate of copper the reaction takes 

 place at a lower temperature. The imperfection of our apparatus has hitherto pre- 

 vented us from estimating the respective quantities of chlorine, hydrochloric acid, aque- 

 ous vapour, contained in the gases issuing from the apparatus ; neither have wo been 

 able to estimate exactly the degree of temperature at which the reaction takes place. 



Many other processes have been used with more or less success for the genera- 

 tion of chlorine. Thus, peroxide of manganese may be acted on by a mixture of 

 hydrochloric and nitric acids, when chlorine, water, and nitrate of manganese will be 

 obtained ; this nitrate, on calcination, reproduces peroxide of manganese and some of 

 the lower oxides of nitrogen, which, by the action of air and water, may again bo 

 oxidised to nitric acid. When a concentrated solution of chloride of magnesium 

 (specific gravity 1-436) is mixed with peroxide of manganese, a product is obtained 



