March 1, 1921 



THE INDIA RUBBER WORLD 



409 



bitumens, gums, and like substances which have hitherto been 

 employed, with the result that the toughness and flexibility of the 

 products are considerably increased. 



(6) Coal-tar dyestuffs and even natural dyes like chlorophyll, 

 which, with a few exceptions, are destroyed by the hot cure and 

 also by the sulphur chloride cure, can be introduced into rubber 

 mixings to be cured by the new process with the production of 

 delicately-tinted materials hitherto quite unobtainable. 



The process possesses the advantage of extreme simplicity and 

 its translation from the laboratory to the works sliould pro\o a 

 simple matter. 



The process can be extended to the vulcanization of rubber in 

 solution. If a solution of rubber in benzol or naphtha be satu- 

 rated wholly or partially with hydrogen sulphide and mixed with 

 a solution of sulphur dioxide in the same solvent, the liquid sets 

 in a few moments to a stiff jelly, and on eliminating the solvent 

 by evaporation a fully vulcanized rubber is obtained. The use 

 of the mixed solutions for producing perfectly vulcanized seams 

 and joints has proved highly successful, and inner tubes repaired 

 by the new. process have an excellent life. 



Further, by the use of the solution process, reformed leather 

 soles and heels may be attached to boots without the aid of stitch- 

 ing or nailing. In fact, an entire boot may be produced from the 

 reformed leather without stitch or nail being necessary. 



PRACTICAL WORKING OF THE PROCESS 



Mr. Peachey said that in working the new process the two 

 gases are introduced separately, both being comparatively easily 

 soluble in the solid rubber, especially the sulphur dioxide. The 

 amount of sulphur dioxide absorbed by rubber is surprising. 

 Hydrogen sulphide is more than sufficiently soluble to yield a 

 coefficient of vulcanization up to hve, which was higher than re- 

 quired in practice. Adsorption is not relied upon at all, but 

 absorption of the gas followed probably by solution. Generally 

 speaking, excess gases, as far as could be judged by smell, are 

 driven out of the rubber after about one hour's exposure. The 

 practice has been followed throughout of giving the shorter sul- 

 phur dioxide treatment first, finishing up with the hydrogen sul- 

 phide in excess, so that there was very little possibility of free 

 sulphur dioxide remaining and practically no danger of free acid 

 forming. 



To get a fully vulcanized rubber it was only necessary to intro- 

 duce 2K' per cent of sulphur; therefore the amounts of the two 

 gases required to vulcanize a mixture containing 50 per cent of 

 rubber were surprisingly small, and a negligible amount of water 

 only is produced. The water diffuses out of the rubber quite 

 rapidly. It never exists in the liquid form in the finished product, 

 and the vulcanization need not be followed by any drying opera- 

 tion. Exposure to the air for a few hours causes all necessary 

 elimination of water. 



As regards the free sulphur present in antimony sulphide and 

 ultramarine, it is disadvantageous to have free sulphur present in 

 a mixing which is to be vulcanized by the new process. It tends 

 in some way sympathetically to convert the atomic sulphur into 

 molecular sulphur. In all mixings made for the new process ordi- 

 nary sulphur would not be present, and the use of antimony sul- 

 phide would be especially avoided, as that substance could be re- 

 placed by much better and brighter colors. In the "dry" treat- 

 ment the rubber or rubber mixing to be vulcanized is exposed to 

 sulphur dioxide for ten minutes, after which a very short ex- 

 posure to the air is given to remove the adsorbed gas from the 

 surface. The material is then introduced into another chamber 

 where it is exposed to the hydrogen sulphide for 20 to 30 minutes. 

 In the case of "solution vulcanization," it is very easy to prepare 

 standard solutions, and in practice a standard solution of sulphur 

 dioxide is prepared by weight. It is convenient to use a solution 

 containing 0.8 per cent of this gas in benzene. Saturate a 10 per 

 cent rubber solution with hydrogen sulphide, and mix four vol- 

 umes of the hydrosen sulphide solution containing the rubber with 



one volume of the benzene solution. The actual proportion of 

 the two gases interacting is theoretical. Small amounts of free 

 sulphur are invariably formed in the rubber. The combination is 

 not quite complete, as apparently a small amount of the atomic 

 sulphur is changed into molecular sulphur, but the amount is 

 small compared with the amount left in the rubber by the "hot" 

 process. 



It was a matter of surprise to learn tliat one experimenter with 

 the new process found acid in his samples ; possibly he used the 

 sidphur dioxide in excess. Mr. Peachey, in his own experiments, 

 invariably kept the hydrogen sulphide in excess, and by treating 

 the rubber first with sulphur dioxide and then with hydrogen 

 sulphide the formation of any trace of free acid can be avoided. 

 If, however, faulty working leads to the formation of a trace of 

 free acid the material can be treated with ammonia, just as in the 

 sulphur chloride process. 



The question of the treatment of rubber one inch in thickness is 

 rather beyond the present limits of the process. The porosity of 

 a mixing is actually greater when fairly heavily loaded, and the 

 penetration obtained is surprising. Although exact diffusion fig- 

 ures were not available, it might be assumed that both sulphur 

 dioxide and hydrogen sulphide diffuse into rubber at least as 

 rapidly as carbon dioxide, and in the case of sulphur dioxide more 

 rapidly. One would not attempt by the new process to deal with 

 material one inch thick, but would avail oneself of the new 

 method of building up which has become possible as the result 

 of the new solution process. 



It is possible now to build up material of any thickness after it 

 has been vulcanized in sheets and to get a solid mass in which the 

 joints will prove of equal strength to that of the material itself. 

 The treatment of thick articles involves new methods of building 

 up, and it is quite desirable that such new methods should be 

 introduced. The leather compounds prepared by this process are 

 2K> times as durable as new leather. 



PRIORITY OF PEACHEY'S PROCESS QUESTIONED 



DUBOSC'S CLAIM 



•yHE eminent French rubber chemist, Andre Dubosc, has put 

 forward a claim' to have anticipated S. J. Peachey's discovery 

 of cold vulcanization of rubber by gases, by his article entitled 

 "An Hypothesis as to the Process of Vulcanization," = which 

 stated, in part, as follows: 



"Sulphur is capable of existing in seven or eight different forms, 

 only one of which, the colloidal form, is in evidence in the vul- 

 canization process. What is used technically is ordinary com- 

 mercial sulphur, which is the polymerized form; evidently there 

 must be a preliminary reaction consisting in the change from or- 

 dinary to colloidal or depolymerized sulphur before the union 

 between the rubber hydrocarbon and sulphur can take place. 



"When pure rubber and sulphur are heated together under or- 

 dinary vulcanizing conditions, the quantity of sulphur entering 

 into combination is very small, and the product has an insignificant 

 strength and elasticity. 



"When rubber containing resins and proteids is healed with 

 sulphur under the same conditions, sulphur is fixed by the rubber 

 ill nominal amounts and the product has the well known properties 

 of vulcanized rubber. 



"When resins are heated with sulphur, hydrogen sulphide is 

 produced and with the 'insoluble portion' of crude rubber, con- 

 sisting of proteids and oxidized rubber, the reaction produces 

 hydrogen sulphide and sulphur dioxide. 



"The role of resin, the insoluble part of rubber, or a metallic 

 oxide, is simply to give rise to the production of sulphur dioxide, 

 hydrogen sulphide, and metallic sulphides. By this means the 

 octatomic sulphur is transformed into the monatomic form which 



'The Tmlia Rubber Journal, January 22. 1921, page 21. 

 . '-^ Caoutchouc ct la Gutta-Percha. March IS. 1915, pace SfiOl. Transli- 

 M<in in Thf India Ri-hhcr Journal, May 1. 1915. AlMtracts in The India 

 Rubber World, May 1, 1915, page 428. 



