Oct., 1913. ] CURRENT TOPICS. 475

Fixation of Nitrogen by Alumina and Carbon. TUCKER and READ. (Amer. Electrochem. Soc. Trans., xxii, 57.)--The object of the investigation was to discover whether nitrogen would combine with a heated mixture of alumina and carbon, or with the products arising from the heating of such a mixture, and to study the best conditions for effecting the reaction. The first experiments were made in a wire-wound electric resistance furnace. In order to obtain higher temperatures a granulated carbon furnace was used, through which a tube passed for holding the charge, heated by a single-phase alternating current. At first several porcelain tubes were used, embedded in the granular carbon resistor. These porce- lain tubes were unable to stand the sudden changes in temperature. This was overcome by the use of a graphite tube, with a bore ~ inch in diameter. This tube had accurately-fitted stoppers of graphite, through which the nitrogen was passed by means of metallic tubes threaded into the stoppers. The charge was contained in a graphite boat. From the result of the few experiments given it is clear that, under proper conditions, there should be no difficulty in producing aluminum nitride containing 30 per cent., or even more, nitrogen. This should be preferable to calcium cyanamide, which averages 17 to 20 per cent. fixed nitrogen.

Atmospheric Electrification during Dust Storms. V. H. JACK- SON. (Nature, xci, 213.)--At Patna, in North India, the westerly winds, which occur in the daytime from the middle of March till June and raise a great deal of dust, are associated with a large nega- tive potential gradient. On one occasion a negative gradient of about 165o volts/m was measured. It is concluded that probably from 9 A.~1. to 6 P.M. on the majority of days from March to June the potential gradient over a large portion of Northern India is negative and very large. This association of negative potential gradient with dust storms is similar to that found by Rudge in South Africa.

Law of Volatility in Chemical Reactions. C. ]V[ATIGNON'. (Comptes Rendus, clvi, 1536.)-Matignon generalizes Berthollet's " law of volatility" in the following form : " Every system of liquid or solid bodies, which is capable of giving rise to a system containing volatile substances, will undergo reaction in that sense at a convenient temperature." The reaction 2 A1 + 3 MgO ~-~ 3 Mg + Al20 ~ is pos- sible because magnesium is quite volatile at comparatively low tem- peratures. In the same way it is probable that barium oxide will be reduced by silicon, owing to the relative volatility of the barium produced. The law can also be extended thus: A reaction which has volatile bodies in its initial stage and also in its final stage is facilitated when the number of volatile molecules in the final stage is greater than that in the initial one,---4.e., of two reactions which are equally endothermic, the one complying with this condition will take place at a lower temperature.