LIME AND CEMENT INDUSTRIES 653 



sometimes go 10 or 12 miles from a railroad. When limestone 

 is used, tlie cylinders generally seem to be made higher. In 

 'New York state dolomites are available in Westchester, Dutchess, 

 Monroe and St Lawrence counties specially. 



Glass-manufacture 



The lime contained in glass is commonly added to the mixture 

 in the form of crushed limestone, this being preferable to the 

 burned rock, which may change in composition by the absorption 

 of water or carbon dioxid from the air. Limestones containing 

 iron oxid or magnesium carbonate should be avoided, since the 

 former colors the glass and the latter makes it less fusible. Dolo- 

 mitic limestones are used, however, in glass-making. 



ISText to silica lime is the most important of glass-making ma- 

 terials, as it renders the soda and potash of the glass less soluble 

 and promotes the fusion of the materials, thus improving the 

 quality. 



Glass rich in lime requires a higher temperature to melt and, 

 because of this, is more destructive to the pots, but, used in 

 proper proportions, lime promotes the fusion, aids in the decom- 

 position of the materials and improves the quality of the glass. 

 Lime glass can not compete with lead glass in brilliancy, but it is 

 harder, not so easily scratched, holds its polish longer, is more 

 elastic and consequently tougher, will stand higher temperature, 

 resists better the action of water and chemical agents, and is 

 much more cheaply produced. On account of the slight differ- 

 ence in specific gravity of the two substances composing it, lime 

 glass is also less liable to striation. In the manufacture of plate 

 glass, which is ground and polished, it is found that glass which 

 is rich in lime is harder to polish than that poor in lime, but holds 

 its polish better and longer, and also increases its resistance to 

 weathering, as well as preventing it from '' sweating ", which 

 happens m glass having an excess of alkalis. It may devitrify 

 from the presence of excess of lime, as when an excess of lead 



