P.C.E. values of ternary mixtures of potash feldspar, soda feldspar, and flint were determined and results shown on a solid phase diagram. No eutectics were developed with either of the binary series of feldspar and flint. The soda feldspar-flint mixtures were more refractory than were those of the potash feldspar series. At least 20% flint variation with potash feldspar will show no change in P.C.E. values and a t least 10% with the soda feldspar showing the unreliability of P C.E. to indicate the amount of the quartz content.
The method used involved the addition of increasing amounts of kaolin to fixed amounts of feldspar and the addition of increasing amounts of quartz to fixed amounts of feldspar. All compositions were examined microscopically and the presence of undissolved kaolin was shown by the appearance of mullite needles, while the presence of undissolved quartz was shown by the presence of cristobalite. Soda feldspar is a better solvent for both quartz and clay than potash feldspar. The solution of quartz in soda feldspar starts at about 1350°C and increases with the temperature until at 1425°C. 32 parts of quartz per 100 of feldspar are dissolved. The solution of quartz in high potash feldspar does not start until 1400°C and only 4 parts are soluble at 1425°C to every 100 parts of feldspar. The solution of clay in soda feldspar starts at 1225°C and increases with the temperature until at 1425°C thirty-six parts are soluble. The solution of clay in high potash feldspar starts a t 1250°C and at 1425OC the solubility is 20.5 parts per 100 of feldspar. The zolution of quartz in porcelain bodies starts at the same temperature as it does in the pure feldspar which the body contains. The amount of solution per unit of feldspar is much greater. The general trend of one of the boundary lines in the ternary system K20-A1203-Si02 has been found.The literature on the subject is completely reviewed.
The articlc describes a quick microscope method for determining the average parThe method is an adaptation ticle size of ground materials under 200-mesh in size. of the blood-count cell or haemarytometer.
Laboratory freezing and thawing tests (A.S.T.M. test No. C4744 and modifications thereof) were correlated with results of outdoor-exposure tests. This correlation was based on saturation coefficient, absorption, rate of absorption, strength, and method of manufacture. New York building brick of the soft-mud and stiff-mud types were investigated. The results show that those brick within a specific absorption range and with the greatest strength and the smallest saturation coefficient will have lower loss in the freezing-thawing tests.
The possible sources of error in the blending of feldspars are discussed and the constancy of the soda-lime ratio in commercial feldspars is demonstrated. All pottery feldspars seem to contain nearly the same type of plagioclase which has a soda-lime ratio of approximately 5.25. It is recommended that this value (Na,O/CaO = 5.25) be used in checking feldspar analyses for accuracy.
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