112 On the Manufacture of Glass. 



Art XV. — On the Manufacture of Glass; by Horatio 

 N. Fenn,* M. D. 



CRUCIBLES. 



It is usual in all Glass Houses, for the manufacturers to 

 make their own crucibles. The difficuhy and importance of 

 this branch cannot be duly estimated, by those who have never 

 been practically acquainted with the manufacture of glass. If 

 the pottery is bad every thing is in confusion : not only the first 

 cost of the materials, but the labor of their preparation, and 

 the expense of the workmanship is entirely lost. If on the con- 

 trary, the crucibles are well made, the manufacturer knows 

 beforehand the products of his fabrication, and directs it to 

 the greatest advantage. He can regulate the action of the 

 heat, vary at pleasure the vitrifiable materials, and in fact 

 manage and control the entire operation at will. It is all 

 important therefore, that the pottery should receive the strict- 

 est attention that it may be as perfect as possible. 



In the first place it is essential that the materials for the 

 pots, should be of the very best quality. There are still im- 

 ported into this country, for the consumption of our glass 

 houses, three kinds of clay ; the white and blue German^ 

 and the English blue clay. They are all of the class called 

 porcelain clays. The blue clays derive their color from car- 

 bonaceous matter, as they all become white in the furnace. 

 Our own country furnishes numerous localities of clay, which 

 are often substituted for those imported. The only kind 

 which I have seen used, is the Philadelphia or New Castle 

 clay, which I am informed is obtained on the Delaware River, 

 near New Castle, below high water mark. 



This clay is brought to us in masses as large as one's head ; 

 it is white, with rose colored spots of various sizes, scattered 

 through the body of it. These . spots are evidently caused 

 by oxide of manganese — as on exposure to the heat of the 

 furnace, they become black. It is very infusible, and when 

 mixed in certain proportions with the other clays, it forms a 

 preferable compound for pots to either of them alone. 



* Dr. Fenn having been practically concerned in the manufacture of glass, 

 has communicated the following observations for this Journal, at the request of 

 the Editor. 



