202 ON SUPERHEATED STEAM. 



free sulphur is eliminated. A coating is found of 

 sulphuret of iron, pretty equally in all cases. 

 Where water is used, it is charged with the sul- 

 phuretted hydrogen to a considerable extent ; but 

 where only steam is used, it takes up but a small 

 quantity, and forms with the steam a less elastic 

 vapour, but with equal capacity for heat. I have 

 also found, that with water and heat at high 

 pressure, the plaster of Paris, which is sulphate of 

 lime, becomes changed ; that is, the sulphur of 

 the rubber joins with the sulphuric acid of the 

 plaster, and mixes with the water. Sulphur, of 

 which the rubber contains a portion, is, as you 

 know, next to oxygen, the strongest chemical 

 body, and has, like it, a powerful affinity for all 

 other elements ; and as the rubber has more than 

 it requires, the heat in hardening it sets it free, 

 and its action is more or less active as it is mixed 

 with more or less water, to bridge it over under 

 pressure and heat to its restless combinations. In 

 the vulcanizer, pressure sufficient is procured by 

 the atmosphere of steam, and a certain amount of 

 pressure is necessary, as it prevents the separation 

 of the rubber by means of the gas formed in it by 

 the sulphur and hydrogen, and which, as it forms, 

 distends out the rubber, when there is no pressure, 

 into small holes. 



With sub-saturated steam only in the vulcanizer, 

 a pressure of 50 or 60 lbs. to the inch, or of higher 

 or lower pressure, is of no consequence, as it 



