The Index of Refraction of Some Soda‐lime‐silica Glasses as a Function of the Composition 1

Twenty‐one soda‐silica and twenty‐one soda‐lime‐silica glasses were made in platinum crucibles and the index of refraction and chemical compositioii of each glass were determined. From the data obtained equations were derived and a diagram was prepared showing the relations between index of refraction and composition of these glasses. The diagram makes it possible to predict with considerable accuracy (1) the index of refraction of any glass in the range of compositions considered, from its composition. and (2) the cwpositions of the various glasses which have the same index of refraction. Some evidence is presented indicating that index of refraction of the soda‐silica glasses may be a simple function of certain soda‐silica compounds which may be present in glass.