A PRELIMINARY REPORT ON CLAYS OV VLORIDA 85

 Sulphur-The determination of sulphur is rarely made in the analysis of a clay unless it is being considered for the manufacture of Portland cement. It sometimes occurs, however, in clays and when present is usually in the form of sulphate or sulphide. Orton and Staley' concluded, from a series of experiments carried on by them, that sulphur retained in the clay during the period of burning, regardless of its form or cause of retention, is not likely to cause any physical disturbance until a fairly complete degree of vitrification is reached, but when a dense vitrified state is reached it soon becomes less dense, on account of the formation of multitudes of minute vesicles in the viscous body, and finally the body becomes spongy and worthless. They further conclude: "That in clays of low sulphur content, and of favorable structure for oxidation, the amount of sulphur left in the clay at vitrification is very small. Hence the period of good structure is long, the vesicular structure develops slowly, and the clay is said to stand overfiring well.
 "In some clays of high sulphur content or of dense structure unfavorable for oxidation, or of high content of iron and carbon, the escape of sulphur is prevented, the clay has a narrow period of usefulness, or none at all, and the vesicular structure becomes enormously exaggerated."
 Soluble Salts-Soluble salts is a term applied to those compounds readily soluble in water which are found in practically all clays to a greater or less degree. Upon being dried the moisture in the clay carries these compounds to the surface where it leaves them, upon evaporation, as an efflorescence. This effloresence or white coating may also occur in the burned product after exposure to moisture.
 The term "effloresence" and "scum" have hitherto been used interchangeably to describe the accumulation of the salts (coating) upon the surface where they have been brought in solution and deposited upon the evaporation of the water. Parmelee2 suggests that the usage of the term effloresence be limited only to include those surface deposits of salts that accumulate on raw clays in their original beds or in storage bins; all those surface deposits which occur in the drying of the ware,


 IThird Report of Committee on Technical Investigation, National Brick Makers' Association, Indianapolis, 1908.
 2Parmelee, C. W., Soluble Salts and Clay Wares, an address before the IndianaIllinois Division of the American Face Brick Association. Chicago, April 11, 1922.