April, rgzj.1 U. S. BUREAU OF CHEMISTRY NOTES. 557

an excess (I molecular equivalent) of Bronner acid, instead of the theoretical equivalent; (4) elimination of heat and alkali treat- ments necessary in former processes to render the dye soluble.

As shown by practical clinical tests, the dye prepared by this process is suitable for blood-volume determinations.

The Spectrum of the Aurora Borealis and the Higher Regions of the Atmosphere. L. VEGARD. (Phvs. Z&t., Dec. 15, rg24.)- Every normal man loves a fight whether *it be a battle of weapons or of wits. The field of physics is far from being free from such interesting contests, and from each conflict there emerges a fact confirmed or a theory established. The discussion between Pender and Cremieu a score of years ago and that more recent one between Duane and Compton upon the change of the wave-length of X-rays by scattering will serve as illustrations. There is now a question in regard to which opinion is divergent, viz., the origin of the green line of the aurora. Vegard, the Norwegian physicist, from his studies of this phenomenon came to the conclusion that solid nitrogen exists in the upper parts of the atmosphere and that it emits the green line (JOUR. FRANK. IXST., Dec., 1923). To test the truth of his inference he went to the cryogenic laboratory at Leyden and there solidified nitrogen by means of liquid air. This he bombarded with cathode-rays. As to the luminous effects he says, “ When. the veloc- ity of the cathode-rays exceeded a certain limit, I got an intense green glow. The spectrum showed two bands in the green, to which I have given the designations N, and N,, along with a series of bands in the blue and in the violet regions. The green band N, was quite sharp, had a wave-length of 5230 A.U. and was found to match a line in the spectrum that can be seen during brilliant aurora1 dis- plays. The band h', was broader and extended beyond both edges of the strong aurora1 line, 5577 A.U. It could further be seen to possess a structure wherein two maxima were recognizable. Although the lines in the green, particularly those corresponding to the aurora1 lines, had, under the cond’itions of the experiment, the character of bands, nevertheless the agreement between the spectrum of the aurora and the glow of solid nitrogen was so distinctive that I held it beyond doubt that in both cases the same peculiar effect of light was con- cerned.” He learned, in addition, that the bombarded nitrogen gave rise to typical ultra-violet bands such as are found in the aurora1 spectrum, and that the distribution of intensity in them is like that in the am-oral light. An agreement in the red likewise manifested itself.

It seemed that a satisfactory origin for the green line had been dkcovered, but at the Toronto meeting of the B.A.A.A., Aug., 1g24, Professor Maclennan and G. N. Shrum presented the results of their

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investigation of the spectrum of bombarded solid nitrogen that were quite in opposition to those of Vegard (this JOURNAL, Sept., 1924). They searched carefully for the 5577 green line but found no trace of it, though they did get lines or bands of nearly its wave-length. T\iot unnaturally Vegard is unwilling to yield his conclusion until facts beyond dispute compel him to abandon it. He puts emphasis on the very small size of the particles of solid nitrogen in the higher air. In his opinion a “ pseudogas ” exists there, consisting of particles of solid nitrogen that need not all contain the same number of atoms and in which the atoms are held together by such forces as normally bind together the parts of solids. He maintains that an exact agree- ment in wave-length is not to be expected between the bands or lines emitted by such a pseudogas and those coming from the solid nitrogen of the laboratory. He tried to realize in the laboratory the state of separation of the nitrogen particles high above the earth by solidify- ing a mixture of argon and nitrogen, so that each nitrogen particle was separated from its fellows by inactive solid argon. It required but little nitrogen to produce a strong spectrum of that element. Under these conditions the band N, grew sharper with diminishing proportions of nitrogen in the solid mixture, since two weak bands gradually disappeared while the main band (which with its fainter associates formed N.,) not only persisted, but grew nearer in wave- length to the green line of the aurora. Results of a similar character were obtained when solid argon-nitrogen was bombarded by cana rays. He* found the spectrum of nitrogen in this case to contain bands of approximately the wave-lengths that have been photo- graphed by Lord Rayleigh in the light of the sky at night. Vegard accordingly attributes such illumination of the sky to the action of canal or positive rays.

After the cathode-rays have ceased to fall on the solid nitrogen, it continues to glow for some minutes or even for much longer periods. Vegard directs attention to this as an instance of the phosphorescing of an element, a remarkable phenomenon.

If the phosphorescing nitrogen is permitted to warm up gradually from the temperature of liquid hydrogen, it glows very strongly at a certain temperature and the color of the light changes from green to blue. Simultaneously the nature of the solid changes from that of ice to a weakly coherent powder. A modification of the crystalliza- tion has occurred. From studies of the specific heat of the substance it was known that this change takes place at about 35.5” abs. After the alteration of the solid the bands N, and N, are not emitted and phosphorescence is absent. “ This peculiarity of solid nitrogen has very interesting relations to cosmic phenomena. In that region of the atmosphere where the green line of the aurora manifests itself, the temperature must be below 35.5” abs. We thus get a ther- mometer for the highest portions of the atmosphere.”

G. F. S.