CURRENT TOPICS. 203

Copper Al loy Resistant to Acids. ROBERT GRIMSHAW. (The Metal Industry, x, 12, 4 9 8 . ) - - A n alloy of 4o per cent. cobalt and 6o per cent. tin is especially resistant to acids, even to concentrated nitric acid and to this acid mixed with chlorides. I t is, however, so brittle as to be unworkable, and is therefore practically worthless. If, however, this alloy is dissolved in copper, so as to form a new alloy of 80 to 95 per cent. copper and 20 to 5 per cent. of the cobalt and tin, a series of alloys is obtained which may be filed, bored, turned, forged, etc., and also have a high degree of chemical resist- ance. I t has been found preferable to make the cobalt-tin alloy first and then dissolve that in the copper.

Opacity to X-Rays . L. G. DROIT. (Comptes Rendus, clv, 7o6 . ) - -S i lk fabrics were loaded with lead phosphostannate, by the ordinary processes of mordanting with metallic salts. One such

• fabric weighed 266 Gm. per square metre, and 68 per cent. of its weight consisted of mineral matter (lead oxide 34, stannic oxide 24, phosphoric anhydride 8, lime and alkali 2). Two layers of this were found to be so slightly permeable by " s o f t " discharges, and six layers by medium or ordinary discharges, as to form an efficient protection against the injurious effect of X-rays on the skin. At the same time the covering with six layers was sufficiently flexible for work. This fabric had an opacity equivalent to a sheet of copper o.044 mm. thick.

Mel t ing Po in t s of Firebricks and Clays. ANON. (Brass World, viii, 12, 4 3 2 . ) - - T h e Bureau of Standards recently determined the melting points of firebricks in an accurate way. The results are interesting as indicating the commercial value, with regard to their heat-resisting properties, of the various kinds of firebricks. The results obtained were:

Fire clay brick . . . . . . . . . . . . . 1555 ° to 1725 ° C. Bauxite brick . . . . . . . . . . . . . . 1565 ° to 1785 ° C. Silica brick . . . . . . . . . . . . . . . . 17oo ° to 17o5 ° C. Chromite brick . . . . . . . . . . . . . . . . . . . . . 2050 ° C. Magnesia brick . . . . . . . . . . . . . . . . . . . . . 2165 ° C. Kaolin . . . . . . . . . . . . . . . . . . . . 1735 ° to 174 °0 C. Bauxite . . . . . . . . . . . . . . . . . . . . . . . . . . . 182o ° C. Bauxite clay . . . . . . . . . . . . . . . . . . . . . . . . 17o5 ° C. Chromite . . . . . . . . . . . . . . . . . . . . . . . . . . . 218o ° C. Pure alumina . . . . . . . . . . . . . . . . . . . . . . . 2OlO ° C. Pure silica . . . . . . . . . . . . . . . . . . . . . . . . . 175 °0 C. Carborundum . . . . . . . . . . . . . . . . . . . . . . 2700 ° C.

The value of 175 °0 given for silica is not the true melting point, but represents the temperature at which the silica distinctly flows.