SELF-PACKING VULCANITE APPARATUS. 301 



substitution of vulcanizing material for the tem- 

 porary wax or gutta percha model, and the mode 

 of effecting tlie substitution. Soon after I had 

 adopted the use of this substance, I felt convinced 

 that some better or more certain method of pack- 

 ing might be devised than that in general use. I 

 accordingly entered on a series of experiments, 

 and I will now lay before you the result. 



As you are all aware, the ordinary mode of 

 packing is attended with two almost unavoidable 

 evils. We must always introduce between the 

 two halves of our flask more than enough 

 of material to fill the vacancy,, trusting to 

 the escape gates, cut ia the plaster, and power- 

 ful pressure combined with a certain amount 

 of heat, to get rid of th^ superfluous material; 

 but never thoroughly accomplishing this object, 

 A diaphragm more or less substantial intervenes 

 between the halves of the flask, and in every case 

 where this diaphragm occurs, the teeth are just 

 exactly the thickness of it distant from the place 

 originally assigned to them. The other inconve- 

 nience occurs where the case still retains some of 

 its original teeth, and our object being to supply 

 the vacancies in such case. . We all know the 

 difficulty attendant on parting the two portions of 

 the flask, the general result being that the plaster 

 last poured retains the plaster teeth of the model 

 as well as the mineral teeth intended to be in- 

 serted, and thereby increasing the difficulty of 



