September 17, 1896] 



NA TURE 



477 



up with fervency by Colonel (lamlile of St. Helens, and that 

 Colonel Gamble's manager, Mr. F. Bramwell, placed all his 

 experience as a consummate technical chemist and engineer at 

 Mr. Weldon's disposal, and assisted him in carrying his ideas 

 into practice. The result was that a process which many able 

 men had tried in vain to realise for thirty years became in the 

 hands i>f .Mr. Weldon and his coadjutors within a few years one 

 of the {greatest successes achieved in manufacturing chemistry. 



The Weklon process commences by treating the residual 

 liquor with ground chalk or limestone, thus neutralising the 

 free acid and precipitating any sulphuric acid and oxide of iron 

 present. The clarified liquor is run into a tall cylindrical 

 vessel, and milk of lime is added in sufficient quantity to pre- 

 cipitate all the manganese in the form of protoxide. An addi- 

 tional (juantity of milk of lime, from one-fifth to one-third of 

 the quantity previously used, is then introduced, and air passed 

 through the vessel by means of an air-compressor. After a few- 

 hours all the manganese is converted into peroxide ; the con- 

 tents i)f the vessel are then run off; the mud, now everywhere 

 known as " Weldon mud," is settled, and the clear liquor run to 

 waste. The mud is then pumped into large closed stone stills, 

 where it meets with muriatic acid, chlorine is given off, and the 

 residual liquor treated as before. 



\ou note that this process works without any manipulation, 

 merely by the circulation of liquids and thick magmas which are 

 moved by pumping machinery. As compared to older pro- 

 cesses it also has the great advantage that it requires very little 

 time for completing the cycle of operations, so that large 

 quantities of chlorine can be produced by a very simple and in- 

 expensive plant. These advantages secured for this process 

 the quite unprecedented success that within a few years it was 

 adopte<l, with a few isolated exceptions, by every large manu- 

 facturer of chlorine in the world ; yet it possessed a distinct 

 <lra»back, viz. that it produced considerably less chlorine from 

 a given quantity of muriatic acid than either native manganese 

 of good quality or Mr. Dunlop's recovered manganese. At that 

 time, however, muriatic acid was produced as a bye-product of 

 the Le Blanc process so largely in excess of what could be utilised 

 that it was generally looked upon as a waste product of no 

 value. Mr. Weldon himself was one of the very few who fore- 

 saw that this state of things could not always continue. The 

 ammonia soda process was casting its shadow before it. 

 Patented in 1 838 by Messrs. Dyar and Hemming it was only 

 after the lapse of thirty years {during which a number of manu- 

 facturing chemists of the highest standing had in vain en- 

 deavoured to carry it into practice) that this process was raised to 

 the rank of a manufacturing process through the indomitable 

 perseverance of Mr. Earnest Solvay of Brussels, and his clear 

 perception of its practical and theoretical intricacies. A few years 

 later, in 1872, Mr. Weldon already gave his attention to the 

 prublem of obtaining the chlorine of the salt used in this process 

 in the form of muriatic acid. He proposed to recover the 

 an>monia from the ammonium chloride obtained in this manu- 

 facture by magnesia instead of lime, thus obtaining magnesium 

 chloride instead of calcium chloride, and to produce muriatic 

 acid from this magnesium chloride by a process patented by 

 Clemm in 1863, viz. by evaporating the solution, heating the 

 residue in the presence of steam and condensing the acid vapours 

 given off. 



Strange to say, this same method had been patented by Mr. 

 Ernest Solvay within twenty-fours before Mr. Weldon lodged 

 his specification. It has been frequentl) tried with many 

 modifications, but has never been found practicable. Soon after- 

 wards .Mr. Weldon, with the object of reducing the muriatic acid 

 required by his first process, ])roposed to replace the lime in this 

 ])rocess by magnesia, and so to produce a manganite of magnesia. 

 After treating this with muriatic acid and liberating chlorine he 

 proceeded to evaporate the residual liquors to dryness, during 

 which operation all the chlorine they contain would be disengaged 

 as hydrochloric acid and collected in condensers, while the dry 

 residue, after being heated to dull redness in the presence of air, 

 would be reconverted into manganite of magnesia. 



This process was made the subject of long and extensive experi- 

 meius at the works of Messrs. (iamble at St. Helens, but did not 

 realise Mr. Weldon's expectations. It, however, led to some 

 further interesting developments, to which I shall refer later on. 



Those of you who were present at the last meeting of the 

 British .-Vssociation in this city will remember that this Section 

 had the .advantage of listening to a paper by Mr. Weldon on his 

 chlorine process, and also to another highly interesting paper by 



NO. 1403, VOL. 54] 



Mr. Henry Deacon, of Widnes, " on a new chlorine process with- 

 out manganese." And those of you who came with the then 

 President of the Section (Prof. Roscoe) to Widnes to visit the 

 works of Messrs. Gaskell, Deacon, and Co., will well remember 

 that at these works they saw side by side Weldon's process and 

 Deacon's process in operation, and no one present will have for- 

 gotten the thoughtful flashing eyes and impressive face of Mr. 

 Deacon when he explained to his visitors the theoretical views 

 he had formed as regards his process. 



Mr. Deacon had made a careful study of thermo-chemistry, 

 which had been greatly developed during the preceding decade 

 by the painstaking, accurate, and comprehensive experiments of 

 Julius Thomsen and of Berthelot, and had led the latter to 

 generalisations, which, although not fully accepted by scientific 

 men, have been of immense service to manufacturing chemistry. 



Mr. Deacon came to the conclusion that if a mixture of hydro- 

 chloric acid with atmospheric air was heated in the presence of 

 a suitable substance capable of initiating the interaction of these 

 two gases by its affinity to both, it would to a very great extent 

 be converted into chlorine with the simultaneous fonnation of 

 steam, because the formation of steam from oxygen and hydrogen 

 gives rise to the 'evolution of a considerably larger quantity of 

 he.at than the combination of hydrogen and chlorine. Mr. 

 Deacon found that the salts of copper were a very suitable sub- 

 stance for this purpose, and took out a patent for this process in 

 186S. He entrusted the study of the theoretical and practical 

 problems connected with this process to Dr. Ferdinand Hurler, 

 who carried them out in a manner which will always remain 

 memorable and will never be surpassed, as an example of the 

 application of scientific methods to manufacturing problems, 

 and which soon placed this beautiful and simple process on a 

 sound basis as a manufacturing operation. 



In the ordinary course of manufacture the major part — about 

 two-thirds — of the hydrochloric acid is obtained mixed with air 

 and a certain amount of steam, but otherwise very little con- 

 taminated. Instead of condensing the muriatic acid from this 

 mixture of gases by bringing it into contact with water, Mr. 

 Deacon passed it through a long series of cooling pipes to con- 

 dense the steam, which of course absorbed hydrochloric acid, 

 and formed a certain quantity of strong muriatic acid. The 

 mixture of gases was then passed through an iron superheater to 

 raise it to the required temperature, and thence through a mass 

 of broken bricks impregnated with sulphate or chloride of copjjer 

 contained in a chamber or cylinder called a decomposer, which 

 was protected from loss of heat by being placed in a brick 

 furnace kept sufficiently hot. In this apparatus from 50 to 60 

 per cent, of the hydrochloric acid in the mixture of gases was 

 burnt to steam and chlorine. In order to separate this chlorine 

 from the steam and the remaining hydrochloric acid the gases 

 were washed with water, and subsequently with sulphuric acid. 

 The mixture now consisted of nitrogen and oxygen, containing 

 about 10 per cent, of chlorine gas, which could be utilised without 

 any difficulty in the manufacture of bleach liquors and chlorate 

 of potash, and which Mr. Deacon also succeeded in using for 

 the manufacture of bleaching powder, by bringing it into contact 

 in specially constructed chambers with large surfaces of hydrate 

 of lime. Within recent years this latter object has been attained 

 in a more expeditious and perfect manner by continuous 

 mechanical apparatus (of which those constructed by Mr. 

 Robert Hasenclever and Dr. Carl Langer have been the most 

 successful), in which the hydrate of lime is transported in a 

 continuous stream by single or double conveyers in an opposite 

 direction to the current of dilute chlorine, and the bleaching 

 powder formed delivered direct into casks, thereby avoiding the 

 intensely disagreeable work of packing this offensive substance 

 by hand. 



Mr. Deacon's beautiful and scientific process thus involves 

 still less movement of materials than the very simple process of 

 Mr. Weldon, because in lieu of large volumes of liquids he only 

 moves a current of gas through his apparatus, which requires a 

 minimum of energy. The only raw material used for converting 

 hydrochloric acicl into chlorine is atmospheric air, the cheapest 

 of all at our command. The hydrochloric acid which has not 

 been converted into chlorine by the process is all obtained, dis- 

 solved in water, as muriatic acid, and is not lost, as in previous 

 processes, but is still available to be converted into chlorine by 

 other methods, or to be used for other purposes. 



In spite of these distinct advantages, this process took a long 

 time before it became adopted as widely as it undoubtedly 

 deserved. This was mainly due to the fact that the economy in 



