AS APPLIED TO DENTISTRY. 149 



be used with safety at a pressure of 400 pounds 

 to the square inch. 



In France a law exists, making it a fine to use 

 a steam-boiler for driving machinery before it has 

 been stamped by a chief engineer, and under the 

 direction of the Prefet of Police. I accordingly 

 applied to this functionary, who, on viewing my 

 apparatus, replied, " that government had nothing 

 more to do with it than with every cook's tea- 

 kettle.'* 



He remarked further, that its small capacity 

 and the great thickness of metal used, would 

 warrant any one in using it under a pressure of 

 500 pounds to the square inch, and thereupon 

 signified his willingness to attach the ofl&cial stamp 

 to that efiect, if desired. 



FeeUng, as I now do, that there is a special 

 advantage to every one who uses the vulcanite in 

 practice, to fully comprehend all its peculiarities 

 in manipulation, I beg first to state, that with all 

 the attention which I have thus far been able to 

 give to this part of the subject, there are a few 

 points yet unexplained. 



For instance, when a mass of material is to be 

 made hard in vulcanite (say one inch square or 

 thick), it is more than probable that it will come 

 out porous and unfit for use, and yet occupy no 

 more apparent space than if it had come out solid. 



As yet I know of no remedy for this, nor why 



