the specific giavity is0.718@ at 03-40. sure 18730 mm, and density 0 . 2 3 2 7 .
The critical temperature is 296.z0, pres1u. D. B.
Vapor-density of dried mercurous chloride. IT. E. Bake?*. Jour. Chetn. SOL.77, 646 (rpoo).-Carefully dried mercurous chloride gives a vapor-density corresponding to the formula Hg2Cl2and the vapor does not amalgamate gold. D. c.
w.
Theory of the constant-volume gas-thermometer. .I. Rose-Znnes. Phil. Mag. [5] 50, z j r ( r p o ) . -The author points out that the weak point of tlie method adopted by Lord Kelvin in the integration of the fundamental equation for the constant-volume gas-thermometer to infinite values of a and 1 along the isopiestic is that it is necessary to assume that an empirical relation, tvliicli represents the Joule-Thomson effect for a small range, necessarily holds at ally temperature. The author shows that it is possible to obviate this extrapolation by transforming the differential equation before integration. Applying the formula so obtained to calculate the absolute value of the freezing-point of water, the result was found to be in close agreement with the ralue obtained by Lord Kelvin by the constant-pressure gas-therinoineter. The characteristic equation of a nearly perfect gas is treated by making further transformations from the author's differential equation. The paper concludes by discussing IIayer's hypothesis and the difference in the methods adopted by Joule and Lord KelH. T. 0. vin for testing it. Notes on gas-thermometry. P.Chaflpais, Phil. illag. [ 51 50,433 (1900). Owing to the necessity of using nitrogen for high temperature work, the author gives the result of careful nieasurenieiits on the coefficient of dilatation of nitrogen. The maximum divergence from the nornial hydrogen scale between oo and 1 0 o O is 0 . 0 1and ~ 40° C. The coefficient reaches a minimum value at Boo C and then increases. A determination of the sulphur boiling-point by the constant-volume nitrogen thermometer showsjt to be 4 4 j . z 0 C instead of the value obtained by Callendar and Griffiths, i. e., 444.53' C. This the author attribates to various causes enumerated in the paper at some length. The consequences of so radical a change in the sulphur point if found to be correct would considerably influence the values of air-temperature as measured with platinum electrical thermometers. The value of 6 in the different formulas, equal to I .so for a standard sample of wire, calibrated according to tlie Callendar-Griffiths method, would require to be changed to I . j j S on the assumption of the author's valw of the S. B. P. H. T. E . Preparation of pure hydrobromic acid. A . Scott. Jour. Chem. SOL.77, 648 ( r 9 w ) .-Since phosphorus almost invariably contains arsenic, the author rv. D. B. advocates the sulphur dioxide method.
Two-Component Systems The allotropic changes of alloys of iron and nickel. L. Dumas. Cornpies Y C C ~ ~ ~ 130, U S , z3z1 (1900). -Up
to 25.84 percent of nickel, the points of irre-
