150 ON THE VULCANITE EASE 



it is made porous ; nor can I conceive why a mass 

 made tlius — even like a sponge — should not ne- 

 cessarily occupy more space than the same mass 

 or bulk would if it had been perfectly sound. 



To make myself more clear, we will take two 

 plaster moulds from an English walnut ; fill both, 

 and vulcanize under an equal degree of tem- 

 perature, observing that the manipulation and 

 conditions are equal throughout the preparatory 

 process. On examination, we find that one is 

 solid, and of the usual weight of vulcanized 

 material, while the other is exceedingly porous, 

 except over the surface, and of much less weight 

 than the sound one, and still both measuring the 

 exact size. 



The cause of all this is somewhat a mystery, 

 and it is not yet known what properties of the 

 material are lost, to make so great a diminution 

 of weight and solidity. In fact, the chemical 

 change of the material under heat, and under 

 any circumstances, is not, I believe, much under- 

 stood. 



As regards changing the vulcanite, so as to 

 make it approximate to the natural colour of the 

 gums, I will not tire you by relating the numerous 

 experiments I have made to attain this desirable 

 object. I have found, however. 



First. That sulphur alone does not change in 

 a vulcanizing heat. 



