Proceedings of the Polytechnic Association. 829 



lay down track twelve times as fast as the usual rate by hand, and it 

 will do the work at less expense. 



The items drew out some discussion,, after which the association 

 adjourned. 



October 22, 1868. 



Professor S. D. Tillmax in the chair ; Mr. C. E. Emsey, Secretary, 



Dental Plates. 



Dr. A. Preterre exhibited specimens of dental plates. The 

 material of one of the plates was aluminum which was made in the 

 required form by casting. Considerable discussion arose on the 

 difficulty of soldering aluminum especially with any otlier material 

 than the old silver solder. A superior solder was stated to have been 

 recently discovered. The otlier specimen of dental plate was made 

 of collodion, rendered solid, the material being called " Parksine," 

 after Mr. Parks its discoverer. Tlie collodion for this purpose ^is 

 imported in thin sheets, and dissolved to a pasty mass in sulphuric 

 ether, and then placed in molds, and subjected to pressure, until the 

 evaporation of the ether reduces it to a sold form. The use of India 

 rubber plates are found^to be objectionable on account of the Vermil- 

 lion (sulpliide of mercury) used in its manufacture inducing salivation 

 in those using such rubber plates. The plate made of collodion is 

 perfectly light in the mouth, as it adapts itself to it quite readily. 



Dr. J. B. Kich remarked that this process of making collodion 

 plates bids fair to be a most wonderftil improvement. It appears to 

 be a very great advance on the rubber plan. It is yQvy light and 

 elastic, and then it is very tough. The only difficulty is the color ; 

 the process for coloring it is a secret. The plates are |)ure collodion. 

 The new material possesses the advantage that if one tooth breaks, 

 another can be pressed in. The casts are made in a pasty condition. 



The chairman remarked that gold was considered the best material 

 for plates, however lie had lately heard a lady, who had artificial 

 teeth set in a gold plate, complain of a coppery taste produced in the 

 mouth by the plate. 



Dr. A. Preterre said this was due to the gold plate being too 

 much, alloyed with copper. Eighteen carat gold has no unpleasant 

 taste. 



Dr. J. B. Rich stated that he has a case, a lady .who could keep 

 rubber gums in her mouth. There are many conditions of the mouth 



