Dec., 1928.1 CURRENT TOPICS. 869

Transition Temperature of Carbon Tetiachloride. JAMES E. MCCULLOUGH and HARRIS E. PHIPPS of Oberlin College (Jour. Am. Chem. Sot., 1928, 50, 2213-2216) have determined that pure solid carbon tetrachloride passes from the cubic to the monoclinic system at a temperature of - 48.54 f 0.02’ C. The hold in the time-temperature curve at this transition point has approximately the same duration as that at the freezing point. This transition point is suggested as a fixed point in thermometry.

J. S. H.

Atomic Weight of Cesium. THEODORE W. RICHARDS and MARCEL FRANCON (Jour. Am. Chem. Sot., 1928, 50, 2162-2166) have purified the cesium alums by recrystallization, and then con- verted them into cesium chloride. Analysis of the cesium chloride by comparison with silver has given the value 132.81 for the atomic weight of cesium.

J. S. H.

Formic Acid. ALBERT SPRAGUE COOLIDGE (Jour. Am. Chem. SOL, 1928, 50, 2166-2178) has determined the vapor density of formic acid which probably was 99.99 per cent. pure. The results indicate that the vapor is an ideal mixture of two gases, having single and double molecules, respectively.

J. S. H.

Infra-red Absorption by the Sulphydrate Group. JOSEPH W. ELLIS of the University of California (Jour. Am. Chem. Sot., 1928, 50, 2 I 13-2 I 18) has determined the infra-red absorption spectra of several alkyl and aryl mercaptans and sulphides, using a recording quartz spectrograph. The mercaptans are characterized by a single absorption band at 1.99 to 2.00 microns, which is not given by the corresponding sulphides. This band and another band, which occurs at 3.8 to 3.9 microns, are considered to be due to the presence of the sulphydrate (-SH) group, radical, or bond.

J. S. H.

Electricity Produced by the Friction of Glass with Solid Ele- ments. P. E. SHAW AND C. S. JEX. (Proc. Royal. Sot., A 779.) To get reliable data of the sign and quantity of the electrical charge caused by rubbing two solids together it is necessary to have materials of known composition and physical structure and of definite surface cleanliness. The rubbing should be done by machine to assure uniformity of method. Glass surfaces were cleaned by boiling in chromic or nitric acid for 1.5 minutes or an