TEE ANALYST, 163 APPARATUS. pressure Regulator for Distillations under Diminished Pressure. W. (Oesterr. Clzem. Zeit., 1902, v., 55.)-This is an apparatus designed to keep the pressure inside a distillation-flask automatically constant within certain limits, so that variations in boiling-points, etc., may be avoided. A and B are charged with mercury, and S and D lead to the pump and distilling apparatus. Before beginning to exhaust, the stopper of A is removed, and the vessel is lowered till it is completely full of mercury ; theu, carefully excluding air, the stopper is put back. The pump is next set going, and when a sufficient vacuum has been attained (say, 20 millimetres) A is raised until the mercury in B touches the lower end of the tube D, thus producing a Torricellian vacuum in A.If, now, the pump becomes more powerful, so that the pressure falls to, say, 15 milli- metres, the mercury takes the positions indicated by the dotted lines; but the pressure in the distillation apparatus remains unchanged, because the interposed mercury column, 5 millimetres in height, neutralizes the difference. Conversely, if by evolution of gas or otherwise, the pressure in the apparatus rises to more than 20 millimetres, the pump at once reduces it again. For more highly reduced pressures, such as 5 millimetres or less, the mercury may be replaced by petroleum oil, which is much lighter, and possesses no considerable vapour tension. Bwstyn. F. H. L. Preparation of a Fine-grained Filter-paper. E. Reale. (Gazz. chim. Ital. , 1901, xxxi. [a], 452; through Chem. Zeit. Rep., 1902, 68.)-Such a paper may be prepared 8s follows : A filter is placed in a stoppered funnel, filled with ammonium sulphide, and the sulphur thrown down with 1 : 2 sulphuric acid. After standing five minutes164 THE ANALYST. the cock is opened, the liquid run off, and the paper washed thoroughly with water. Such a, prepared filter-paper will be found useful for many purposes. F. EL L.