88 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

firing may prevent the concentration of the salts on the surface of the buck or using a reducing flame in the kiln may counteract the ill effects aftimes. Coating the ware with some organic substance such as rubber, tar, or flour is often satisfactory. Washing the clay in much the same nrnner as is followed in the sedimentary kaolin mines in Lake and Putn'im Counties will usually accomplish the desired result, but this method isIsomewhat expensive except for high-grade wares. Probably one of tffe most satisfactory methods of prevention is to convert the soluble seats into insoluble compounds. This can be accomplished by reactions with barium compounds. For example, if a clay containing calcium sdlphate is treated with barium chloride the insoluble barium sulphate Aid calcium chloride results. The calcium chloride is decomposed in burning without harmful results. There are several ways in which this general method can be applied.


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