C. E Munroe — Artificial Hematite Crystals. 485 



Art. XLVI. — Artificial Hematite Crystals ; by Charles E. 



Munroe. 



In Deacon's process for the isolation of chlorine hydrogen 

 chloride is decomposed by passing it, in the state of a gas, over 

 a " contact " substance which practically acts as a conveyor of 

 oxygen from the air to the hydrogen chloride, so that the 

 reaction appears to result onlv in the oxidation of the HC1 as 

 follows: (HCl),+O a =(H a O) a +(Cl a ) a . The most satisfactory 

 " contact " substance for use in this art is cupric chloride, for 

 when heated to 400° C, it dissociates into cuprous chloride 

 and chlorine (CuCl a ) 2 =Cu. 2 Cl a + Cl 2 . On exposing the cuprous 

 chloride to oxygen, cupric oxide is formed and the remainder 

 of the chlorine is liberated in accordance with the following 

 equation: Cu 2 Cl a + O a =(CuO) a -f-Cl 2 . If now the cupric oxide 

 be exposed to hydrogen chloride gas it reacts with it, forming 

 cupric chloride and water as follows (CuO) a +(HCl) 4 = (CuCl a \ + 

 (H„0)„, so that the " contact " substance is regenerated and 

 the cycle of changes begins anew. Theoretically it is unneces- 

 sary to employ an external source of heat in the process after it 

 is once begun, because while 32 calories are absorbed in the 

 dissociation of the cupric chloride 60*4 calories are evolved in 

 the two subsequent reactions, showing a gain of 28 - 4 calories 

 for the C} 7 cle, but in practice it is found advantageous to heat 

 the air and hydrogen chloride up to 400° or 500° C. before they 

 are brought to the contact substance. 



Although there are differences in the details of the different 

 apparatus in which this manufacture is carried on commer- 

 cially, yet they in general consist of a salt-cake pan or retort, in 

 which the hydrogen chloride is liberated ; a set of cooling pipes 

 and drying tower, in which the moisture is condensed; super- 

 heaters, in which the gases are heated in iron pipes, set in masonry, 

 to the desired temperature ; the " decomposer " or " digester, " 

 containing the contact substance absorbed in porous material, 

 where the above reactions take place ; and the condensing 

 apparatus and coke towers for drying and purifying the chlorine. 

 As the catalytic substance becomes inactive after a time, the 

 process is interrupted every two or three months and air is 

 passed through the heated pipes to the contact mass to regen- 

 erate it. 



A Belgian apparatus of this general description had been 

 employed in the generation of chlorine at the Ammonia Com- 

 pany's works in Philadelphia for about seven years when the 

 iron heater pipes about the digestor became burned through. 

 This was evidently due to the action of the heated air and sul- 



