AS APPLIED TO DENTISTRY. 151 



Second. That pure vermilion, which is the only- 

 suitable colour now used, does not of itself 

 change. 



Third. That sulphur and vermilion mixed in 

 any proportions do not change. 



Fourth. That rubber alone does not change. 



Fifth. That rubber and vermilion mixed do not 

 change. 



Sixth. That rubber and sulphur, when mixed 

 and hardened, invariably produce a substance jet- 

 black. 



Seventh. That the three combined, in certain 

 proportions, will change but slightly in colour, 

 at a temperature sufficient to produce a substance 

 in hardness equal to leather. And, 



Eighth. That gutta-percha used alone, and in 

 the manner just referred to relative to rubber, 

 produces nearly similar results. 



Therefore we may reasonably infer from these 

 facts, and others, that the chemical change (if it 

 is such) which the rubber itself undergoes to 

 obtain the necessary solidity and strength, im- 

 parts a degree of, or covers up by its own inlcy 

 hlachiess, such colours as do not in themselves 

 change. 



Again : to those somewhat familiar with the 

 process, there are important queries often arising 

 touching the condition of the water in an appa- 

 ratus after it has been used for a length of time. 

 Whether it receives or not, and retains, any vul- 



