ii. 44 Analytical Chemistry. Purification of Filter Paper by Hydrofluoric Acid. A. GAWALOWSKI (Zcitsch. nizcll. Chew., 1915, 54, 5OS).-Treatment of filter-paper with hydrofluoric acid results in the removal of silica, but any calcium and iron salts which may be present are converted into their respective fluorides ; calcium fluoride is insoluble, and ferric fluoside is very slightly soluble in water, and although the latter may be removed by prolonged washing of the, paper care must be taken

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... t the wash-water is free from even traces of ammonium, potassium, or sodium salts, since these convert the ferric fluoxide into a still less soluble double salt. The, hydrofluoric acid solution used t o remove the silica from the paper should be very dilute, and the paper should then be washed thoroughly; otherwise the paper becomes "hardened." W. P. S. Use of the Colouring Substance of Red Cabbage as a n Indicator. ECKERLIN (Chem. Zentr., 1916, ii, 489-490 ; from Mztt. I<. L u m k m n s t . Wcuserhygienc, 1915, 58-69).-A solution of the indicator is obtained by boiling red cabbage, leaves for thirty minutes with three times their weight of water, filtering the extract, and, after cooling, neutralisiiig i t with N / 100-potassium hydroxide solution. The indicator is green in alkaline solution and red in acid solution; a t the neutral point, in the presence of alkali salts, the colour is bright blue, although the neutral indicator itself is violet. The indicator solution may be preserved by the addition of 0.2% of chloroform o r 0.9% of phenol, and should be stored in the dark (compare A., 1913, ii, 237, 522). w. P. s. Some New Indicators for the Colorimetric Determination of Hydrogen Ion Concentration. HERBERT A. LUBS and WILLIAM MANSFIELD CLARK (J. Wc~shiizgton Acnd. Sci., 1915, 5, 609-617).-The authors have pxepared and investigated a number of substances of the methyl-red type with the object of ascertaining their use for the estimation of the hydrogen-ion concentration in bacterial media. Among those newIy prepared were : monoethycred [ethylamino b enze?ze-o-a.zob e?izoic acid], which gives colour changes over the range P'r, 4*25--Pf, 6.00; diethyl-red (diethylaminobenzeneo-azobmzoic acid), colour changes over the range Pf, 4.50-Pb 6 -5 0 ; monopropyl-red, for the range Pf 4.25-Pk 6.25; and dipro&-Activation of Chlorate Solutions by Osmium. 111. Separation of Rydrogen and Methane, Catalysis of Mixtures of Hydrogen and Oxygen. K. A. HOFMANN and OTTO SCHNEIDER (Ber., 1915, 48, 1585-1593. Compare A. , 1913, ii, 62, 609).-The behaviour of various noble metals towards oxidisable gases in the presence of chlorate solutions has been studied. Preparations were made by evaporating the salts of the metlals, in quantities equivalent t o 1 gram of potassium osmate, to dryness with formic acid, and then adding a solution containing 15 grams of sodium chlorate and 2 grams of sodium hydrogen carbonate to 100 C.C. These mixtures were tested against the gases in a Hempel pipett'e. Towards hydrogen, the activity decreased in the order P t , Rh, Ru,