GLASS-MAKING. 159 



Although, glass is supposed to be a fairly definite chemical com- 

 pound, each manufacturer has his own notions on the subject, 

 and occasionally he changes his mind, or perhaps his supplies 

 come from a different locality. The result, in either case, would 

 be a slight change in the composition of the batch. A typical 

 mixture would be for every hundred parts of fine white sand 

 about forty parts of alkali (carbonate of soda), ten parts of burned 

 lime, and forty parts of red lead. 



It will be noticed that the batch is essentially different from 

 that used in the manufacture of window and Of bottle glass. It 

 differs both in the character and the quality of the materials em- 

 ployed. The ingredients common to the several mixtures must 

 be much purer for use in the production of table and household 

 glassware of the finer grades. Care is taken that the sand shall 

 contain no iron ; and, in order to free it from any admixture of 

 loam or other disadvantageous earthy materials, it is subjected to 

 a washing process before it is brought to the mixing-room. By 

 this treatment the more finely divided matter, such as clay and 

 the like, is carried off with the water, while the coarser sand settles 

 to the bottom of the washing-troughs. Further, in the selection 

 of the alkali, the cheaper sulphate of soda is never substituted for 

 the carbonate, as is frequently done in the manufacture of bottles. 



In the processes of the atelier the competition is a question of 

 quality rather than of quantity. The element of human labor is 

 so large that it would not be economical to expend it upon an in- 

 ferior grade of glass. The workers, or rather the men who direct 

 them, go on the principle of those wise domestic economists who 

 reflect that the cost of labor in making up clothing is approxi- 

 mately constant, and who therefore do not feel that they can 

 afford to buy shoddy. 



The earthy materials — sand, alkali, and lime — give substance 

 and transparency. Fused together, they form ordinary glass. 

 The additional ingredient, the red lead, has a special function to 

 perform It has for its immediate object an increase in the weight 

 of the glass ; and since in general an increase in weight means 

 an increase in refracting power, its ultimate object is an additional 

 brilliancy in the product. Every one has noticed the heaviness 

 of cut glass ; or, if he has not, and enters a shop to buy a piece of 

 it, the shop-keeper is very apt to call his attention to the fact — 

 particularly if the price be correspondingly heavy — assuming that 

 weight is an undeniable guarantee of quality and brilliancy. If 

 you object to the price, he puts the piece into your hands and 

 says confidingly, " Just feel the weight of it ! * The argument is 

 a pertinent one, but not altogether conclusive, for there are many 

 other elements besides weight upon which the merit of the prod- 

 uct depends. It is quite possible to have the glass too heavy for 



