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The system: K2OPbOSiO2
Dec., I93¥]
U. S. ]~UREAU OF STANDARDS NOTES.
75I
The values obtained to date show t h a t : (a) an appreciable variation of MgO content did not significantly alter the water absorptivity of the heated bodies, this property being influenced m u c h more, relatively, by the CaO and by the alkalies in the feldspar; (b) the total linear shrinkage was decreased, for specimens heated to I26O ° C., from a m a x i m u m of 8 per cent. for a body containing no talc to a m i n i m u m of 0.7 per cent. for a body containing 43 per cent. talc. T h e shrinkage, also, was influenced significantly by the CaO in the amphibole and the alkalies in the feldspar; (c) moisture expansion was practically eliminated, but this must be accounted for in part by the low feldspar content; (d) the total linear thermal expansion to 700 ° C., considering specimens heated to 1260 ° and 1325 ° C. only, was decreased from a m a x i m u m of 0.93 per cent. for a body containing neither alkalies nor MgO to 0.35 per cent. for a body containing I5 per cent. amphibole. In general the thermal expansions increased as the percentage of talc or of amphibole was increased over 30 per cent. and, other factors being equal, expansions of bodies containing talc were higher t h a n of the comparable bodies of the amphibole series.
T H E SYSTEM:
K~O-PbO-SiO~.
A preliminary survey of this system indicates t h a t it contains three ternary compounds having the molecular ratios I :2:2, I :3:6, and I : I :4, respectively. T h e first, crystallizing as hexagonal plates, is uniaxial negative, has indices 1.93 4- o.oi, 1.72 4- o.oI, and the optic axis perpendicular to the cleavage. T h e second, crystallizing as well defined fibers or lathes and resembling a short fibered asbestos when crushed, has indices ranging from 1.69 4- o.oI to 1.79 4- o.oi, extinction is parallel, and the optic axis is parallel with the longitudinal axis. The third crystallizes as rectangular, platy granules of parallel extinction, and the indices range from 1.59 4- 0.005 to 1.65 4- 0.005. It is probably biaxial. T h e linear thermal expansion to 300 ° C., and the softening temperature, of the three compositions, as glasses, are respectively: 0.46 per cent. and 395 ° C. ; 0.28 per cent. and 46I ° C. ; and, 0.24 per cent. and 517 ° C.
U. S. ]~UREAU OF STANDARDS NOTES.
75I
The values obtained to date show t h a t : (a) an appreciable variation of MgO content did not significantly alter the water absorptivity of the heated bodies, this property being influenced m u c h more, relatively, by the CaO and by the alkalies in the feldspar; (b) the total linear shrinkage was decreased, for specimens heated to I26O ° C., from a m a x i m u m of 8 per cent. for a body containing no talc to a m i n i m u m of 0.7 per cent. for a body containing 43 per cent. talc. T h e shrinkage, also, was influenced significantly by the CaO in the amphibole and the alkalies in the feldspar; (c) moisture expansion was practically eliminated, but this must be accounted for in part by the low feldspar content; (d) the total linear thermal expansion to 700 ° C., considering specimens heated to 1260 ° and 1325 ° C. only, was decreased from a m a x i m u m of 0.93 per cent. for a body containing neither alkalies nor MgO to 0.35 per cent. for a body containing I5 per cent. amphibole. In general the thermal expansions increased as the percentage of talc or of amphibole was increased over 30 per cent. and, other factors being equal, expansions of bodies containing talc were higher t h a n of the comparable bodies of the amphibole series.
T H E SYSTEM:
K~O-PbO-SiO~.
A preliminary survey of this system indicates t h a t it contains three ternary compounds having the molecular ratios I :2:2, I :3:6, and I : I :4, respectively. T h e first, crystallizing as hexagonal plates, is uniaxial negative, has indices 1.93 4- o.oi, 1.72 4- o.oI, and the optic axis perpendicular to the cleavage. T h e second, crystallizing as well defined fibers or lathes and resembling a short fibered asbestos when crushed, has indices ranging from 1.69 4- o.oI to 1.79 4- o.oi, extinction is parallel, and the optic axis is parallel with the longitudinal axis. The third crystallizes as rectangular, platy granules of parallel extinction, and the indices range from 1.59 4- 0.005 to 1.65 4- 0.005. It is probably biaxial. T h e linear thermal expansion to 300 ° C., and the softening temperature, of the three compositions, as glasses, are respectively: 0.46 per cent. and 395 ° C. ; 0.28 per cent. and 46I ° C. ; and, 0.24 per cent. and 517 ° C.