The crystals described in this note were formed in the course of some experiments on the volatilization of iron from clay pots used for the melting of optical glass. In order to reduce the amount of iron introduced by solution of the pot walls, experiments1 were made on the removal or iron from the pot itself by the action of chlorine at the temperature of the pot arch (1000 to 1100° C.). Chlorine was led into the suitably covered pot for several hours. In some preliminary experiments the pot was removed from the furnace immediately after the chlorine treatment and a deposit of crystals of hematite was found on the outer upper portion of the pot, where the effluent chlorine and ferric chloride vapor had come into contact with the products of combustion, which filled the (gas-fired) furnace. On the inside of one of these pots minute glittering crystals were found which subsequently were identified by chemical, optical, and crystallo-graphic characters as rutile, one form of titanium dioxide.