AS APPLIED TO DENTISTRY. 155 



soap-stone, feldspar, silex, and asbestos, without 

 being able to perceive any considerable advantage 

 over plain plaster. 



I have also mixed with it large and small quan- 

 tities of sulphur, with a view of using less in the 

 vulcanite compound, but could never determine 

 that it produced any change whatever in the cha- 

 racter of the piece within. 



To make the plaster model hard, I have used 

 a solution of alum, at other times a solution of 

 silicate of potash, but with no special effect. 



To make the plaster separate more cleanly and 

 readily from the piece after vulcanizing, I have 

 used upon the model a solution of silex, glass, gum 

 arabic, gum copal, and almost every other known 

 gum, without practical benefit, and only find sul- 

 phuric acid, simply applied after the work is 

 vulcanized, to act the most effectually. 



It has been suggested '' that the use of vermi- 

 lion in the material gives us in the piece one of 

 the forms of mercury, and that with those who 

 cavil at trifles, serious objections would arise 

 against its use." 



We reply, that if the work decomposes, wears 

 away to any extent, or absorbs the fluids of the 

 mouth one jot or tittle — which has yet to be proved, 

 then I submit it for your decision as to what 

 extent of injury can possibly arise to those who 

 wear it ? 



In conclusion, I beg to state that these and 



