112 On the Manufacture of Glass. 
Art XV.—On the Manufacture of Glass; by Horatio 
N. Fenn,* M. D. 
CRUCIBLES, 
Ir is usual in all Glass Houses, for the manufacturers to 
make their own crucibles. The difficulty 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 
i it therefore, that the potter ild receive the strict- 
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 
