The procedure of casting glass pots has been described by several contributors to THIS JOURNAF.~ It is the pqrpose of the present paper to call attention to several points of practical importance. The characteristics of a casting slip as well as of the fired body depend, first, upon the composition-the content of grog, kaolin, ball clay, and feldspar; second, the sizing of the grog; third, the peculiar physical and chemical qualities inherent in primary kaolins as differentiated from the secondary ones, and in ball clays against the fire clays; fourth, the amounts and proportions of sodium silicate and carbonate of soda. The following mixtures have been used successfully in the Pittsburgh Laboratory of the Bureau of Standards for the casting Mixture No. I .

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