REVIEWS The object of this department of t h e J o u m a l is to issue, a s p ~ o m f l t b aspossible, critical digests of all Journal articles which bear upon any phase of Physical Chemistry. S t r z d w e Phenomena Experiments with Rontgen Rays. A . Voller and B. Walter. Wied. Ann. 61, 88 (1897). A Crookes' tube with very high vacuum is a good source of the rays, and gives off but little heat ; tubes have been coiistructed which could be used continuously for an hour without becoming sensibly warm. Reproductions are given of two photographic plates of the shadows cast by twenty-two substances, the first set being taken with a cool tube and the other with the same tube warmed (from without). T h e rays from the cool tube, although producing no more effect on the unprotected plate than those from the other, evinced much greater power of penetrating the specimens. Many attempts have been made to measure the wave length of the Rontgen rays by means of certain phenomena generally ascribed to optical interference. T h e results so obtained by various investigators differ very widely, and the authors adduce evidence to show that the phenomena in question are not due to interference at all. On the other hand, as the refractive index of the diamond (for ordinary light 2.4 to 2 . 5 ) is found to be I 0.0002, an application of Helmlioltz's theory of dispersion shows that, if Rontgen's rays consist of transverse waves, their length can not exceed one onemillionth of a millimeter. The ability to cause diffuse reflection of the rays was tested with twenty-one chemical elements, and appears to stand in close connection with the position of the latter in Mendelejeff's table. W. L. M.
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Reviews
792
Cathode and Rontgen Rays. J. Precht.
Wied.
A m .61,330
(1897). The paper begins with a series of photographic records of
the paths of the cathode rays under the influence of magnets : the results agree with the requirements of Biot-Savart's law. Turning to Rontgen's rays, the author confirms the conclusions of other experimenters with respect to their non-refrangibility and their action on a steam jet and on a selenium cell : he finds that the degree of fluorescence caused by them depends largely on the presence of slight impurities in the fluorescent substances, and that in certain cases it requires some time to reach its maximum. Calcium platinocyanid is the most fluorescent substance met with but the potassium salt is best for increasing the sensibility of photographic plates. Photographs of a large number of minerals show that their transparency to the Rontgen rays depends not merely on their thickness and density, but also on their chemical composition. The Rontgen rays differ from the cathode rays in producing no coloration in crystals of sodium chlorid, and from Lenard's rays in exciting no fluorescence in pentadecyl-paratolyl-ketone. Lastly, a study of certain interference phenomena (?)leads to a wave length of 370 - 850 x IO.-' ( ( A s transverse waves of these lengths can not penetrate paper, Rontgen's rays probably consist, in part at least, of longitudinal waves)). L. M.
w.
On the Absorption of Light by Crystals. V, Agafonow. Comtes rendus, 125,87 ( ~ 8 9 7 ) . With pure compounds the absorption at the violet end increases with the complexity of the salt. No data are given.
w.D.3.
On the Change of Salts by Cathode Rays. 18. Abegg. Zeit. E'lect?-ochemie,4, 118; Wied. Aim. 62,425 (1897). T h e author attributes the changes in the color of the alkaline halids, under the influence of cathode rays, to the forniation of new modifications. T h e solubility of the yellow sodium chlorid seemed to be the same w D.B. as that of the unchanged salt.
