568 U. S. RUREAU OF MINES NOTES. [J. F. I.

2835 metres per second, the density of the lead was reduced from I I .383 to I I .228. It is believed, that this reduction in dens’ity is concomitant to the formation of minute voids in the lead, and further investigation is required to determine this. This confirms tests made in the winter 1888-1889 at the Massachusetts Institttte of Technology by Robert C. Williams and J. C. Seager, and reported by Frederick W. Clark in the Transactions of the Ameri- can Iwtitutc of Mining Engineers, vol. xviii, pp. 526, 527, in which the specific gravity of lead cylinders before firing was I I .5 I and after firing a charge of explosive in the borehole in the lead cylinder, the specific gravity was’ I 1.268.

Production of Ammonia by Synthesis.-The economic pro- duction of ammonia from nitrogen and hydrogen directly will be a valuable addition to chemical industries. The Haber-Le Ros- signal process has been brought to a high degree of perfection, and it is claimed that Germany relied almost entirely on it for the supply of nitrogen compounds during the war. American chemists have given considerable attention to it also. Briner and Baerfuss, in a lengthy paper in Jour. d. Chim. Phys. (vol. xvii, p. 71, 1919), give results of experiments on the union of nitrogen and hydrogen under the influence of the electric arc, the gases being under diminished pressure. They summarize the results as follows :

At pressures of not over 150 mm. of mercury, the arc assumes a sheath form, the length being, of course, dependent on the cur- rent strength and the pressure. This form has a powerful influ- ence on the determination of the synthesis. Changes of pressure and of the metal used for electrodes affect the output of ammonia. The experimenters believe that the combination takes place be- cause the molecules of the two gases are dissociated into the constituent atoms in the region of the arc. The reduced pressure favors this action and, therefore, contributes materially to the production of ammonia. The dissociation may be due to the heat alone, or result from more complex conditions. The condition described by Strutt, Proc. Roy. Sot. (vol. lxxxv, p. 219, 1911, et seq.), namely, the formation of ahotropic nitrogen of high activity, was not observed in these experiments. The best results should theoretically be obtained by the use of a mixture of the elements in the proportion in which they exist in the compound, i.e., N to H,, but as both elements are not equally activated by the arc, it is likely that in practice an excess of nitrogen should be present as this is less activated than hydrogen.

H. L.