CHEMISTRY. 169 



lime, and by decomposing by heat the resulting chloride of mag- 

 nesium into magnesia, for use over again, and chlorhydric acid. 

 In this form, the process is capable of yielding all the chlorine 

 contained in the acid employed, and apart from mechanical loss 

 employs no materials except coal and air, which are not used over 

 and over again. Experiments on a small scale promise well for 

 the value of this modified process. 



Deacon's Process. If a mixture of chlorhydric acid and oxygen 

 be sufficiently heated, portions of the hydrogen and oxygen com- 

 bine, and chlorine is set free to a certain small amount. This 

 proportion is very much increased by passing a heated mixture 

 of these gases over certain substances which influence this reac- 

 tion without being themselves, as far as appears, affected by it. 

 Copper salts possess the power of bringing about this reaction in 

 a very marked degree, sulphate of copper being most conven- 

 iently employed. All the compounds of lead, with the excep- 

 tion of the sulphate, act in the same way, although requiring a 

 higher temperature. All the manganese compounds act simi- 

 larly, but the temperature required is so elevated that all the 

 liberated chlorine is not obtained as such, a certain amount appar- 

 ently recombining with a portion of the hydrogen of the water 

 formed. 



It is proposed to make use of these facts in the commercial pro- 

 duction of chlorine, by passing the mixed gases over common 

 bricks soaked in a saturated solution of sulphate of copper, and 

 then dried. It has been found that the chlorhydric acid, as 

 evolved from the ordinary salt-cake apparatus, contains, mixed 

 with it, a sufficient quantity of air for the reaction to take place. 

 It has been found that iron resists very completely the action of 

 chlorine in the decomposing apparatus. A common iron gas- 

 pipe, exposed to the heated chlorine for several months, shows 

 no appreciable wear. The chlorine produced is mixed with a 

 large proportion of nitrogen, but no difficulty is anticipated in the 

 making of bleaching-powder, if the saturation is brought about 

 systematically by allowing the strong gases to meet lime nearly 

 saturated, and then passing the weaker gases over fresh lime. 

 Any undecomposed chlorhydric acid is removed by passing the 

 gases through water, the dilute acid formed dissolving only mere 

 traces of chlorine. Abstract of a paper read before the British 

 Association, 1870, by Henry Deacon. 



Hargreaves 1 Process. Mr. James Hargreave, of Witlness, has 

 devised a method for producing chlorine without the use of ox- 

 ide of manganese. He has a process for the separation of phos- 

 phorus from the iron slag produced in the puddling operation of 

 the iron manufacture. In carrying out this process the iron slag 

 is treated with chlorhydric acid, and thereby protochloride of 

 iron in solution is obtained as a by-product. This solution is 

 evaporated to dryness, and the dry protochloride, by slow appli- 

 cation of heat with access of atmospheric air, becomes perchloride, 

 which undergoes decomposition, yielding chlorine and peroxide of 

 iron. This process yields an equivalent of chlorine for each equiv- 

 alent of chlorhydric acid employed. 



