mesh, pulped with water containing the usual proportion of reclaimed mill liquid, treated counter-current with dilute SO, roaster gas containing a large excess of oxygen over the amount necessary to completely oxidize all sulphites formed. Thus all difficulties met with in the aforementioned processes from the for- mation of unstable complex copper salts are avoided. No attempt is made to regenerate the leaching solutions; the sulphur supplied finally goes to waste as sulphates of the acid-soluble constituents of the ore, and as iron sulphates formed cluring precipitation of dissolved copper on iron.

Sulphur dioxide made from any convenient source, such as native sulphur, massive pyrite, or concentrate carrying upwards of 20 per cent. sulphur, may be utilized. If smelter gases con- taining 2 per cent. SO, by volume are available, they may be utilized direct from the stack. The ordinary volatile impurities found in smelter gases, such as arsenic and antimony, are not detri- mental in this application of SO, leaching. Further details are given in a report issued by the Bureau in mimeograph and in more complete form in Technical Paper ,112, now in course of publication.

ACETYLENE NOT A PRECIPITANT FOR CYANIDE SOLUTIONS.

By John Gross.

1~ connection with some investigations being made by the Bureau of Mines, on the precipitation of gold and silver from cyanide solutions, it was suggested that the effect of acetylene for this purpose be investigated.

The acetylene used in the tests was from commercial calcium carbide. Experiments resulted in more or less complete precipi- tation of silver, but no gold.

As silver acetylene, obtained by precipitating the silver from an ammoniacal solution of silver nitrate by acetylene, is yellowish white, easily soluble in cyanide and highly explosive, and the pre- cipitate obtained from the cyanide solutions was black, not soluble in cyanide and not explosive, it was decided to investigate the nature of the silver precipitate from the cyanide solutions. Ill

preparing a large quantity of the precipitate it was found that after complete precipitation of the silver the solution contained

116 C. S. BUREAU OF MINES NOTES. [J. F. I.

soluble sulphides. This provided a clew and after appropriate tests the precipitation was proved to be silver sulphide.

The conclusion drawn was that a small amount of hydrogen sulphide was contained in the acetylene and that this was the active precipitating agent. Other tests were made, all of which verified the conclusion that acetylene, free from hydrogen sulphide, had no precipitating power on cyanide solutions of silver or gold. Further details are given in a recent report issued by the Bureau.

A Photographic Spectrum of the Aurora of May 13-15, 1921, and Laboratory Studies in Connection with It. LORD RAYLEIGH. (Proc. Royal Sot., A 709.)-A very good photograph of the spec- trum was obtained on the tight of May 14. On the plate there appears a trace of a continuous spectrum, to be attributed to moon- light, the negative nitrogen bands in the blue, the violet and the ultra-violet and yellow-green aurora line. Strangely enough the bands are stronger than the line. When the spectrum of krypton was photographed on the same plate its characteristic line appeared in “approximate coincidence” with the aurora1 line.

It was not found possible to reproduce in the laboratory the nitro- gen bands as they manifested themselves in the light of the aurora. Through excitation of nitrogen by atomic rays a good imitation was got, but other spectra of the gas persisted in appearing under the conditions of experiment. The cathode ray spectrum in nitrogen was free from these spectral interlopers but the distribution of inten- sity among the bands was not the same as in the aurora.

“ We have reason to believe, not indeed from direct experiment, but on very strong theoretical grounds, that the upper atmosphere, in which the aurora occurs, is rich in the lightest constituents of air, helium and (possibly) hydrogen. Do these constituents appear in the aurora1 spectrum? The photographs reproduced confirm clearly all previous evidence that they do not. We are faced, therefore, with the alternatives that either they are not there, or that the conditions of excitation are not such as to develop the spectrum. According to all laboratory experience, even a trace of hydrogen asserts itself in the spectrum of any kind of an electric discharge through air, under any conditions of pressure.” The origin of the aurora is nqt deli- nitely known. “There is a good deal of evidence from the work of Birkeland, Stormer, and Vegard, for attributing the aurora to cathode rays from the sun.” An objection to this explanation, is that, as stated above, in the laboratory cathode rays fail to give the desired distribution of intensity in the band spectrum of nitrogen. On other grounds the author finds it very difficult to account for the origin of the aurora on the basis of excitation by atomic rays, even though these in the laboratory do give the same intensity distribution as that in the aurora1 spectrum. G. F. S.