Procebdings of the P oLYTECHyic Association. 1045 



5. Certain materials are used for improving or purifying the glass, 

 such as the binoxyd of manganese, nitre, and arseneous acid, white 

 arsenic. Oxyd of lead, in the form of minium, is principally used in 

 flint glass, as it increases its brilliancy, the purity of its color and the 

 power of its refraction. The binoxyd of manganese, was formerly 

 known as glass-maker's soap ; its effect is ascribed to the facility with 

 which it gives up its oxygen, which combines with the coloring 

 principles and destroys them. In other words, it converts the pro- 

 toxyd of iron, which would give the glass a dark green color, into a 

 sesquioxyd, which is of higher oxydation and which leaves the glass 

 cleaner. 



Borax and boracic acid, as also the borate of lime, called Hayesine, 

 from Peru, are like the Chili saltpeter, very useful and powerful 

 agents for accelerating the fluxing of the silex. 



The silex mostly used in England is sea sand, and not river sand, 

 as is extensively used in the United States ; it consists chiefly of 

 quartz, and the finest qualities are obtained from Alum Bay, in the 

 Isle of Wight, and from near Lyon, on the coast of JSTorfolk ; the 

 black flint, when raised- to a red heat, and plunged in cold water, is 

 frequently used, and probably gave the name to a species of glass, 

 flint glass or crystal glass. 



The color is imparted to glass by the application of the metallic 

 oxyds, and when the coloring is put into the pot so as to pervade 

 the mass, it is termed pot metal, in distinction of such colors as are 

 in the form of enamel or coating on the outside of the various uten- 

 sils, such as sticks, plates and ornaments. 



The oxyd of eohalt produces a blue color. 



Peroxyd of manganese produces a violet color. 



Oxyd of antimony produces a yellow color, 



Oxyd of uranium, a canary or opaline greenish color, 



Cassius purple, or oxyd of gold, produces a pink, or pink red 

 color, also called the ruby color. 



Oxyd of chromium produces green. 



Copper protoxyd, produces a dark red or ruby color, while the 



Copper oxyd, or black copjier, produces a green color. 



Silver produces a pure and beautiful yellow, but it can only be 

 produced in the fire of a mutfle, and that by staining the surface. 



The manufacture of glass is divided into several classes : 



A. Window glass, which includes, 

 1. Crown glass. 



