112 



THE INDIA RUBBER WORLD 



[January i, 1904. 



SULPHUR IN ITS RELATION TO VULCANIZATION.* 



OF all the materials used in the manufacture of rubber 

 goods, Sulphur, next to Rubber itself, is not only the 

 most interesting by reason of the great variety of states 

 it is able to assume, but it is the one whose reactions 

 both in the vulcanizing process and in kindred combinations 

 should be more generally understood by manufacturers. The 

 better manufacturers are acquainted with the characteristics of 

 the materials used by them, the better they will be enabled to 

 avoid mistakes, to improve the quality of their products, and, 

 what is of the greatest importance, to more easily discover the 

 causes of defective goods that are occasionally made even in 

 the best conducted establishments. 



It is now generally conceded that in the vulcanizing opera- 

 tion Rubber and Sulphur chemically unite. We have therefore 

 as a result of this operation a Rubber sulphide, as we have Hy- 

 drogen sulphide as the result of the combination of Hydrogen 

 and Sulphur, and Iron sulphide as the result of the union of 

 Iron and Sulphur. The Hydrogen sulphide and the metallic 

 sulphides may be formed by a direct union of the elements, 

 assisted by heat, in the same way that Rubber sulphide is 

 formed. 



The velocity of the union of Sulphur with Hydrogen and the 

 metals is increased with each increase of temperature, as is quite 

 universally the case with chemical processes. The converse of 

 this is also true, that with each reduction of temperature, the 

 rate of the union of Sulphur with Hydrogen and the metals is 

 decreased, as it is with chemical processes in general. When 

 we once comprehend fully the nature of the formation of sul- 

 phides by the direct union of the elements, the great mystery 

 surrounding vulcanization disappears. The production of the 

 Rubber sulphide is a simple chemical process — the union of the 

 rubber hydrocarbon with sulphur — brought about by the same 

 means as the production of the other sulphides mentioned. 



The velocity of many chemical processes, besides being ac- 

 celerated by heat, may be accelerated by the presence of other 

 substances which do not pass into the products of the reaction. 

 A well known example of this is the use of Manganese perox- 

 ide in the production of Oxygen from Potassium Chlorate. 

 Oxygen may be obtained from the Chlorate by simply heating 

 it in a flask. But if it be mixed with Manganese peroxide in 

 fine powder, the Oxygen is produced more freely and at a 

 lower temperature, but the peroxide itself undergoes no change 

 in the reaction. In like manner the union of Rubber and Sul- 

 phur in vulcanization is made to proceed both faster and at a 

 lower temperature by adding litharge in fine powder to the 

 compound of Rubber and Sulphur. The litharge does not pass 

 into the products of the reaction, but it enables vulcanization, 

 which would take place more slowly and at a higher tempera- 

 ture without the addition, to proceed at a greater velocity and 

 at a lower temperature. Other substances are sometimes used 

 in place ol litharge, but perhaps none of them with so marked 

 an effect. 



As the velocity of chemical processes of all kinds rapidly in- 

 creases with rising temperature and rapidly decreases with fall- 

 ing temperature, it would naturally follow that the production 

 of sulphides, whether of Rubber or of Hydrogen, and the metals, 

 can take place at lower temperatures than those at which we 

 have been accustomed to observe them. It can accordingly be 



* Copyrighted. 1903, by The India Riiiubr Publishing Co. 



stated that vulcanization can take place at any temperature be- 

 low that ordinarily employed, and above the freezing point of 

 Rubber, if sufficient time be allowed. " We have in general no 

 ground for supposing that any chemical process which can take 

 place at a higher temperature cannot take place at a lower." — 

 (Ostwald.) 



Many of the metallic sulphides can be formed under the in- 

 fluence of pressure without the aid of extraneous heat. When 

 a mixture of Sulphur in suitable proportions with Magnesium, 

 Zinc, Iron, Cadmium, Bismuth, Lead, Silver, Tin, or Anti- 

 mony in very fine powder is subjected to a great pressure, at 

 ordinary temperature, a part of the metal is transformed into a 

 sulphide. If the cake which is thus formed be reduced to 

 powder and the operation be repeated a few times, the 

 entire mass can be converted into a su'phide. Pressure 

 therefore seems to bring about, in this instance, the same 

 result that is brought about by increase of temperature. 

 That is, it hastens the formation of a product that other- 

 wise would be more slowly formed at the same tempera- 

 ture. May we not therefore expect that pressure will hasten 

 the formation of the Rubber sulphide at whatever tem- 

 perature it may be employed ? It was formerly thought that 

 pressure, being purely mechanical, was without influence on 

 chemical reactions, but modern chemistry recognizes its influ- 

 ence on chemical processes in general. 



Native Sulphur exists generally in the neighborhood of vol- 

 canoes, either in amorphous (uncrystallized) or in crystallized 

 masses, or mingled with the earth from which it is separated 

 by simple fusion or by sublimation. It is also emitted in the 

 form of pure Sulphur vapor from many extinct volcanoes of 

 which Mt. Popocatapetl is a well known example. Iron pyrites 

 furnish quite a proportion of the Sulphur of commerce which 

 is separated from the pyrite ores by roasting. 



At Mt. Popocatapetl large quantities of Sulphur are produced. 

 The Sulphur vapors which are emitted from the fissures at the 

 bottom of the crater are conducted through long wooden gal- 

 leries in which they crystallize or condense in beautiful masses 

 of pure Sulphur. As this mountain is about 17,500 feet high 

 and as the bottom of the crater can be reached only by means 

 of a basket and rope raised and lowered about 600 feet by a 

 windlass, the labor of transportation must be very great. But 

 after the galleries are once placed there is no further expense 

 attending the production of the Sulphur. 



Sulphur belongs to that class of substances, called dimor- 

 phous, which can crystallize according to two different systems. 

 When crystallized from solutions it assumes the form of octa- 

 hedral crystals, which are of the same form and appearance as 

 native sulphur crystals that are sometimes found very large 

 and perfectly pure. When crystallized bj slowly cooling from 

 a melted condition, it assumes the form of oblique elongated 

 prisms, which are usually called prismatic. The temperature 

 at which Sulphur is crystallized usually governs the form of 

 the crystals. If crystallized at 212° F. or over, prismatic crys- 

 tals are formed. If crystallized at a low temperature the crystals 

 are octahedral. These different forms cannot, however, in all 

 cases, be explained by the differences in the temperatures at 

 which they have been formed, as both forms are sometimes de- 

 veloped at the same time, from the same solution in carbon 

 bisulphide, when it is -allowed slowly to evaporate. 



Sulphur is chiefly known in the form of Brimstone, Roll 



