4/8 



NATURE 



[September 17, 1896 



the use of muriatic acid which it effected was at the time when 

 the process was brouglit out, and for many years afterwards, no 

 object to the majority of chlorine manufacturers, who were still 

 producing more of this commodity than they could use. More- 

 over, there were other reasons. The plant required for this 

 process, although so simple in principle, is very bulky in propor- 

 tion to the quantity of chlorine produced, and as I have pointed 

 out, the ]3rocess only succeeded in converting about one-third of 

 the hydrochloric acid produced into chlorine, the remainder 

 being obtained as muriatic acid, which had in most instances to 

 be converted into chlorine by the Weldon process ; so that the 

 Deacon process did not constitute an entirely self-contained 

 method for this manufacture. This defect, of small moment as 

 long as muriatic acid was produced in excessive quantities, was 

 only remedied by an invention of Mr. Robert Ilasenclever a 

 short number of years ago ; when by the rapid development of 

 the ammonia soda process the previously existing state of things 

 had been completely changed, and when, at least on the conti- 

 nent, muriatic acid was no longer an abundant and valueless 

 bye-product, but, on the contrary, the alkali produced by the Le 

 Blanc process had become a bye-product of the manufacture of 

 chlorine. Mr. Hasenclever, in order to make the whole of the 

 muriatic acid he produces available for conversion into chlorine 

 by the Deacon process, introduces the liquid muriatic acid in a 

 continuous stream into hot sulphuric acid contained in a series of 

 stone vessels, through which he passes a current of air. He 

 thus obtains a mixture of hydrochloric acid and air, well adapted 

 for the Deacon process, the water of the muriatic acid remaining 

 with the sulphuric acid, from which it is subsequently eliminated 

 by evaporation. In this way the chlorine in the hydrochloric 

 acid can be almost entirely obt.ained in its free state by the 

 simplest imaginable means, and with the intervention of no other 

 chemical agent than atmospheric air. Since their introduction 

 the Deacon process has supplanted the Weldon process in nearly 

 all the largest chlorine works in France and Germany, and is 

 now also making very rapid progress in this country. 



Mr. Weldon, when he decided to give up his manganite of 

 magnesia process, by no means relaxed his efforts to work out a 

 chlorine process which should utilise the whole of the muriatic 

 acid. While working with manganite of magnesia he found that 

 magnesia alone would answer the purpose without the presence 

 of the peroxide of manganese. He obtained the assistance of 

 M. Pechiney, of Salindres, and in conjunction with him worked 

 out what has become known as the " Weldon-Pechiney " process, 

 which was first patented in 1884. 



This process consists in neutralising muriatic acid by magnesia, 

 concentrating the solution to a point at which it does not yet 

 give off any hydrochloric acid, and then mixing into it a fresh 

 quantity of magnesia so as to obtain a solid oxychloride of 

 magnesium. This is broken up into small pieces, which are 

 heated up rapidly to a high temperature without contact with the 

 heating medium, while a current of air is passing through them. 

 The oxychloride of magnesium containing a large quantity of 

 water, this treatment yields a mixture of chlorine and hydrochloric 

 acid with air and steam, the same as the Deacon process, and 

 this is treated in a very similar way to eliminate the steam and 

 the acid from the chlorine. The acid condensed is, of course, 

 treated with a fresh quantity of magnesia, so that the whole of 

 the chlorine which it contains is gradually obtained in the free 

 state. 



The rapid heating to a high temperature of the oxychloride of 

 magnesium without contact with the heating medium was an 

 extremely difficult practical problem, which has been solved by 

 M. Pechiney and his able assistant, M. Boulouvard, in a very 

 ingenious and entirely novel way. 



They lined a large wrought-iron box with fire-bricks, and 

 built inside of this vertical fire-brick walls with .small empty 

 spaces between them, thus forming a number of very narrow 

 chambers, so arranged that they could all be filled from the top 

 of the box, and emptied from the bottom. These chambers they 

 heated to a very high temperature by passing a gas flame 

 through them, thus storing u]) in the brick walls enough 

 heat to carry out and complete the decomposition of the 

 magnesium oxychloride, with which the chamber was filled 

 when hot enough. 



Mr. Weldon himself called this apparatus a "baker's oven," 

 in which trade certainly the .same principle has been employed 

 from time immemorial ; but to my knowledge it had never 

 before been used in any chemical industry. This process has 

 been at work at M. Pechiney's large alkali works at Salindres, 



NO. 1403, VOL. 54] 



and is now at work in this country at the chlorate of potasih 

 works of Messrs. Allbright and Wilson, at Oldburj', a manu- 

 facture for which it offers special advantages. Mr. Weldon and 

 M. Pechiney had expected that this process would become 

 specially useful in connection with the ammonia soda process by 

 preparing in the way proposed by Mr. Solvay and Mr. Weldon 

 in 1872 a solution of magnesium chloride as a bye-product of 

 this m.anuficture ; but instead of obtaining muriatic acid from 

 this solution by Clemm's process, to treat it by the new process, 

 so as to obtain the bulk of the chlorine at once in the free state. 

 But M. Pechiney did no more succeed than his predecessors in 

 recovering the ammonia by means of magnesia in a satisfactory 

 way. 



Quite recently, however, it has been applied to obtain chlorine 

 in connection with the ammonia soda process by Dr. Pick, of 

 Czakowa, in Austria. He recovers the ammonia, as usual, by 

 means of lime, and converts the solution of chloride of calcium, 

 obtained by a process patented by Mr. Weldon in 1869, viz. by 

 treatment with magnesia and carbonic acid under pressure, into 

 chloride of magnesium with the formation of carbonate of lime. 

 The magnesium chloride solution is then concentrated and 

 treated by the Weldon-Pechiney process. 



I have repeatedly referred during this brief history to the 

 great change which has been brought about in the position of 

 chlorine manufacture by the development of the ammonia soda 

 process, and have pointed out that the muriatic acid which for a 

 long time was the bye-product of the Le Blanc process, without 

 value, thereby became gradually its main and most valuable 

 product, while the alkali became its bye-product. 



I have told you how, very early in the history of this process, 

 Mr. Solvay and Mr. Weldon proposed means to provide for this 

 contingency, and how Mr. Weldon continued to improve these 

 means until the time of his death. Mr. Solvay, on his part, 

 also followed up the subject with that tenacity and sincerity of 

 purpose which distinguishes him ; his endeavours being mainly 

 directed to producing chlorine direct from the chloride of calcium 

 running away from his works by mixing it with clay and passing 

 air through the mixture at very high temperatures, thus pro- 

 ducing chlorine and a silicate of calcium, which could be utilised 

 in cement-making. The very high temperatures required 

 prevented, however, this process from becoming a practical 

 success. 



I have already told you what a complicated series of 

 operations Dr. Pick has lately resorted to in order to obtain the 

 chlorine from this chloride of calcium. Yet the problem of 

 obtaining chlorine as a bye-product of the ammonia soda process 

 presents itself as a very simple one. 



This process produces a precipitate of bicarbonate of soda and 

 a solution of chloride of ammonium by treating natural brine, or 

 an artificially made solution of salt, in which a certain amount of 

 ammonia has been dissolved, with carbonic acid. In their 

 original patent of 1838, Messrs. Dyar and Hemming proposed 

 to evaporate this solution of ammonium chloride, and to distil 

 the resulting dry product with lime to recover the ammonia. 

 Now, all that seemed to be necessary to obtain the chlorine from 

 this ammonium chloride was to substitute another oxide for lime 

 in the distillation process, which would liberate the ammonia 

 and form a chloride which, on treatment with atmospheric air 

 would give off its chlorine and reproduce the original oxide. 

 The whole of the reactions for producing carbonate of soda and 

 bleaching powder from salt would thus be reduced to their simplest 

 possible ix>rm ; the solution of salt, as we obtain it in the form of 

 brine direct from the soil, would be treated with ammonia and 

 carbonic acid to produce bicarbonate and subsequently mono- 

 carbonate of soda ; the limestone used for producing the carbonic 

 acid would yield the lime required for absorbing the chlorine, 

 and produce bleaching powder instead of being run into the 

 rivers in combination with chlorine in the useless form of chloride 

 of calcium ; and both the ammonia (used .as an intermediary in 

 the production of soda), and the metallic oxide (used as an inter- 

 mediary in the production of chlorine), would be continuously 

 recovered. 



The realisation of this fascinating problem has occu]iied me 

 for a great many years. In the laboratory I obtained soon 

 almost theoretical results. A very large number of oxides and 

 even of salts of weak acids were found to decompose ammonium 

 chloride in the desired way ; but the best results (as was to be 

 clearly anticipated from thermo-chemical data) were given by 

 oxide of nickel. 



When, however, I came to carry this process out on a large 



