January i, 1904.] 



THE INDIA RUBBER WORLD 



113 



Sulphur, Flowers of Sulphur, Precipitated Sulphur, and Milk 

 of Sulphur. Brimstone is the Sulphur of commerce as im- 

 ported from Sicily. When Sulphur vapor is condensed in a 

 chamber above the melting point of Sulphur, it condenses into 

 a liquid state which, when poured into cylindrical moulds and 

 cooled, is the ordinary Roll Sulphur, and is a mass of prismatic 

 crystals; but if the temperature of the chamber is kept some- 

 what below the melting point of Sulphur, the vapor condenses 

 in the form of a very fine powder which is Flowers of Sulphur. 

 These belong to the amorphous or uncrystallized variety, but 

 they gradually change to the octahedral form. 



Flowers of Sulphur and Milk of Sulphur are not materially 

 different except in appearance. Milk of Sulphur, being formed 

 by precipitation from aqueous solutions, is so finely divided 

 that its color appears to be white, though it is actually yellow. 

 On account of its extreme fineness it is more subject to chem- 

 ical changes. 



These various forms of Sulphur differ not only in appear- 

 ance but in many other respects. Their hardness and density 

 and their melting points differ. They differ in their power of 

 refracting light, in their behavior to solvents, and are different- 

 ly acted upon by heat and by various chemical reagents, though 

 when they enter into combination with other elements they 

 form identical chemical products. 



None of the forms of Sulphur are stable except within cer- 

 tain ranges of temperature. At the ordinary atmospheric tem- 

 peratures all other forms are gradually changed to octahedral 

 and at this temperature this form is the most stable. But if 

 octahedral Sulphur be slowly heated above 205° F. it is changed 

 to prismatic Sulphur. If octahedral Sulphur be plunged in 

 small pieces into a bath at that temperature it melts at 239 , 

 but if slowly heated it fuses at 248 , the melting point of pris- 

 matic Sulphur. 



Above 205 F. prismatic Sulphur is the most stable, and at 

 this temperature all the other forms are changed to it. " These 

 relations show a very great similarity to the reciprocal trans- 

 formation of ice and water, or, generally, to fusion and solidifi- 

 cation. As in those cases, so in the present, there is a temper- 

 ature above which only the one form, and below which only the 

 other form, is stable. On passing this point, therefore, the one 

 form passes into the other, and only at this one temperatuie 

 can the two forms exist together."— (Ost-wald.) 



This point can be varied by pressure. But a very great pres- 

 sure is necessary to make even a slight change. The melting 

 point of Sulphur is also changed by pressure. But, in this case 

 also, great pressures are required to bring the change about. 

 Under a pressure of 519 atmosphere its melting point is raised 

 to 275° F. Thus between 248° and 275 a pressure of 288 pounds 

 per square inch is required to raise the melting point one de- 

 gree, an amount so great as compared with the pressure used 

 in dry air or steam vulcanization, that the effect of pressure in 

 this respect, is of no importance in these processes. A pressure 

 of 20 atmospheres raises the point at which octahedral Sulphur 

 changes to prismatic, one degree. As vulcanization is general- 

 ly carried on considerably above 205°, this effect of pressure 

 may also be ignored. 



Sulphur, however, has no definite melting point, but when 

 heated gradually softens, loses its form, and passes impercept- 

 ibly into the liquid state. Prismatic Sulphurmelts and resolid- 

 ifies at 24s . If the temperature is raised to 290°, it resolidifies 

 at 236°, but if heated to 338°, the point of solidification is 234°. 

 At 248° Sulphur is a clear, limpid, light yellow liquid. But if 

 heated somewhat above this point conversion into a peculiar 

 allotropic modification, called Plastic Sulphur, commences. 

 The Sulphur gradually grows more viscous until at 482° it is so 



thick that it cannot be poured from the vessel in which it boils 

 at 842 , but at no subsequent temperature is it more limpid 

 than at 248 . 



From its behavior, it is inferred that melted Sulphur can as- 

 sume different allotropic forms, as well as in the solid state, 

 though it has not yet been possible to separate them or to 

 describe their properties. 



As Sulphur exists in several different forms both in the solid 

 and in the liquid state, so in the state of vapor it exists in sev- 

 eral different forms with different molecular weights. The con- 

 stitution of Sulphur vapor continually varies with increase of 

 temperature up to 1800°. Above this temperature, the dens- 

 ity of the vapor remains constant at 64 (hydrogen being 1). 

 The combining weight of Sulphur, however, being 32, the 

 entirely dissociated molecules of the vapor must consist of 

 two atoms of Sulphur. Sulphur in this form exists in Sul- 

 phur vapor at the temperatures used in vulcanization, though 

 at those temperatures the proportion both depends upon the 

 temperature and varies with it. It is in this state that Sul- 

 phur vapor combines with rubber in the vulcanizing opera- 

 tion. 



If Mercury and Sulphur in the proper proportions be tritu 

 rated together, the mixture is converted into Mercuric sulphide 

 at ordinary temperature. So if Silver be exposed, at ordinary 

 temperatures, near Sulphur, the result is the black Silver sul- 

 phide on the surface. 



As Sulphur enters into combination only when in solution 

 or in this state of dissociated vapor, it is evident, from the for- 

 mation of Mercuric sulphide, that the entire mass of the Sul- 

 phur is not only vaporized at atmospheric temperature, but the 

 vapor is dissociated into the form assumed when Sulphur forms 

 combinations. It is interesting to know this fact, as it may 

 tend to explain, by analogy, the dissociation of Sulphur, when 

 compounded with rubber, under the influence of a very moder- 

 ate temperature. 



At ordinary temperatures Sulphur emits a sensible vapor. 

 At temperatures slightly above the ordinary it can pass entirely 

 into vapor. The vapor from a few small bags of Sulphur hung 

 up in a grapery is sufficiently powerful to destroy the microbe 

 or fungus that attacks the grapes. So, in the early days of the 

 rubber manufacture, it was found that Sulphur compounded 

 with rubber preserved it from decay, without the use of arti- 

 ficial heat. At 212 the vapor has a considerable tension 

 which is rapidly increased with each increase of temperature. 



As the uncombined Sulphur in vulcanized rubber is neither 

 octahedral nor prismatic, it is evident that after the octahedral 

 crystals have been changed at or above 205° to prismatic, there 

 has been a further change in form. 



Under the microscope, Dr. Weber says that this excess of 

 Sulphur appears like extremely small globules. We should ex- 

 pect the Sulphur to take this form. Rubber, for dry heat vul- 

 canizing, is usually compounded with Sulphur, Litharge, 

 Whiting, besides other substances. On an average perhaps 3 

 per cent, of Sulphur is incorporated with the rubber and more 

 than the weight of rubber in the other mixtures. All of these 

 mixtures are in the finest possible powder, the particles of 

 which can only be observed by the microscope. All of these 

 various particles must be thoroughly incorporated with the 

 rubber. If this operation is performed in an ideal manner, each 

 particle of the compound will be completely enveloped in an 

 extremely thin wall of rubber, and, theoretically at least, each 

 particle of Sulphur will be isolated from each other particle. 

 When this compound is slowly heated in the vulcanizing pro- 

 cess, it seems reasonable to expect that after a temperature of 

 205° F. is passed, all the Sulphur not yet absorbed will be 



