Gums, Resins, 



292 



[Oct. 1906. 



Mr. Ryan :— To put it briefly, ammonia is anti-acid and formalin is antiseptic. 



This concluded the discussion ; and a vote of thanks having been passed to 

 Mr. Bamber for his lecture, those present separated. 



REPORT UPON A VISIT TO GREAT BRITAIN TO INVESTIGATE THE 

 INDIA RUBBER INDUSTRY IN ITS RELATION TO THE GROWTH 

 AND PREPARATION OP RAW INDIA-RUBBER IN THE 

 MALAY PENINSULA. III. 



By P. J. Burgess. 



IN THE HEAT CURE. 



23. The raw rubber and finely-powdered sulphur are mixed together inti- 

 mately on a mixing or a masticating machine. If other ingredients are to be added 

 to the rubber, it is done at the same time that the sulphur is incorporated. Chemical 

 union between the sulphur and the rubber takes place neither during this mixing 

 nor afterwards, as long as the mixture is kept cold. If, however, it be heated to 

 about 800° P. chemical union takes place slowly, and the new product, vulcanised 

 rubber, is formed. By far the greater bulk of rubber is vulcanised in this way. 

 The hot chambers in which the actual heating and vulcanisation are carried out are of 

 several types, and differ in the way in which the heat is applied. Where pressure has 

 to be exerted on the rubber during vulcanisation the goods are vulcanised in moulds, 

 between large plates of iron, which are hollow and heated by steam. In other cases, 

 large chambers heated by steam are used, and into these the rubber goods, placed on 

 trays and smothered in French chalk, are taken. Fabrics coated with rubber -such as 

 sheeting and mackintosh cloth— are wound round a large iron drum and immersed in 

 water, which under pressure is heated to the required temperature. Long tunnels, 50 

 or HO feet long, dry heated by steam, are used for vulcanising hose pipe and lengths of 

 tubing which cannot be coiled. The temperature is regulated so as to slowly rise to 

 about 300° F., and after maintenance at that point for a period varying from half to 

 three hours, it is slowly allowed to drop again. During vulcanisation a portion of the 

 sulphur combines with the rubber and forms the new addition compound, which is 

 quite distinct from raw India-rubber, and from which the sulphur cannot be removed 

 by any known process. Although the whole of the rubber is acted upon by the 

 sulphur to a greater or lesser degree, the action is slow and the whole of the sulphur 

 present is not used up during the short period that the vulcanisation lasts, and 

 free uncombined sulphur remains disseminated throughout the vulcanised product. 

 A prolonged period of heating during vulcanisation diminishes the excess of sulphur, 

 and leads to the production of more highly vulcanised rubber. The more sulphur 

 which vulcanised rubber has used and actually combined with, the darker and 

 harder the product until the extremes of vulcanite and ebonite are reached. From 

 partially vulcanised goods the excess of free sulphur can be chemically extracted, 

 and this is one of the operations in " recovered " vulcanised rubber ; the combined 

 sulphur, however, remains always in the recovered rubber. The recovery of rubber, 

 therefore, is an operation by which the mechanically mixed substances, such as the 

 excess of sulphur and the fillings with which the rubber was mixed in manufacture, 

 are wholly or partially removed, and the residue resulting is worked up into a 

 form in which it can be blended with new rubber, and act as a substitute for 

 a portion. 



COLD CURE. 



24. Although pure sulphur does not combine with india-rubber at a tem- 

 perature below 270° F., yet a compound of sulphur with chlorine— namely, mono- 

 chloride of sulphur— does react on ru bber, and the sulphur is transferred from the 



