JOHN A. WILLIAMS. 251 



Such a sand is found in New Jersey and is the chief 

 source of supply of the Eastern glass manufacturers. 



Ground quartz rock is largely used in the manufacture 

 of flint glass or crystal, its purity causing it to be the best 

 source of supply. Lime may be used either as slaked, 

 burned or carbonate. If the limestone is comparatively 

 pure, it may be used as carbonate to great advantage, 

 however, when impurities are present it should be burned, 

 and if a fine quality of glass is desired it is preferable to 

 slake and sift it. 



Carbonate of soda is the chief alkali employed and is 

 obtained principally from England, although a small 

 proportion of the amount consumed in this country is 

 produced at Syracuse, N. Y. The sulphate of soda is 

 largely substituted for the carbonate when pots are used 

 for melting the batch, since it is much cheaper. The 

 disadvantage to its use, is that it acts very powerfully 

 on the fire clay of which the pots are made, but as the 

 durability of a glass melting pot is limited at the best, 

 its life being from four to eight weeks, it is probably 

 more economical to use a greater number of pots per 

 year, and the sulphate of soda as the flux. In tank 

 furnaces it has been found more advantageous to use the 

 carbonate of soda. 



Iron and aluminum are present in all glasses which 

 have been manufactured from impure materials. They 

 impart a bluish tint to the glass, which is very un- 

 desirable in most cases, as the higher oxides of iron 

 forms an almost colorless silicate, by the aid of such 

 oxidizing agents as MnO', NaNo' and As'O', it is possible 

 to reach such a result. 



The materials used are all carefully weighed so that 

 each batch is a duplicate of the preceding one, and it is 

 then thoroughly mixed by being turned over several 

 times, or by passing through a machine constructed es- 

 pecially for this purpose ; after the mixing is completed, 



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