Chemistry and Physics. 401 



(about 20), and no continuous background can be seen on the 

 plate. The o shortest wave-length recorded photographically is 

 about 1370 A. U. The second spectrogram was obtained when 

 the aluminium electrodes were placed so close to the fluorite 

 window of the vacuum grating-spectrograph as to cause the dis- 

 charge to play along the surface of the window. The exposure 

 lasted six minutes and the fluorite was badly damaged. How- 

 ever, notwithstanding the latter incident, the spectrogram is very 

 good, the lines are much stronger than in the positive first men- 

 tioned, additional lines appear in the neighborhood of A 1300, and 

 a dense, continuous background fills the region from A 1050 to 

 A 1870. In fact, most of the energy seems to be concentrated in 

 the last named interval. (The plates do not extend to wave- 

 lengths greater than 1870 A. IT.) The electrical apparatus used 

 by Lenard was more powerful than that employed by Lyman. 



From another point of view, Lyman has shown in earlier papers 

 that a quartz plate, one or two millimeters thick, is quite trans- 

 parent below 1600, but that it is "absolutely" opaque for wave- 

 lengths shorter than 1400. Furthermore, he has demonstrated 

 experimentally that air is very opaque between 1400 and 1550, 

 but that transparency begins again at about 1350. 



When all of the facts just enumerated are taken into account 

 the conclusion must be reached that the " rays " with which 

 Lenard was dealing consisted in the strong aluminium group at 

 about A 1300. For, Lenard says:* "Die auf Luft wirksamen 

 Strahlen werden also zum weitaus grossten Teile durch Quarz 

 absorbiert, und zwar ausserordentlich viel starker durch den 

 Quarz als durch die gleich dicke Luftschicht, welche er ersetzte." 



The third and last spectrogram illustrating Lyman's paper per- 

 tains to the vacuum-tube spectrum of hydrogen. In obtaining 

 this plate no capacity was introduced in the secondary circuit, a 

 current of about 10 milliamperes flowed, and the gas was at a 

 pressure of about 2 millimeters of mercury. The spectrum con- 

 sists of so many fine lines as to give a nearly continuous, strong 

 and uniform illumination from about A 1330 to A 1640. In the 

 same interval the spark between aluminium electrodes gives only 

 a few scattered lines. Also the hydrogen spectrum has a group of 

 fine lines between A 1230 and A 1290. Consequently, Lyman 

 recommends the hydrogen vacuum-tube for use in experiments 

 on ionization. The fact that Palmer, working with a vacuum- 

 tube, obtained nearly as great volume ionization as Lenard, 

 although the latter had a very powerful transformer, is also 

 accounted for by the foregoing data. — Physlkal. Ztschr., No. 13, 

 July, 1912, p. 583. H. s. u. 



8. On the Apparent Change in Weight during Chemical 

 Reaction. — This question has been recently investigated by J. J. 

 Manlet. Although he gives only an abstract of the original 

 paper, nevertheless the salient points and the final result seem to 

 be of sufficient general interest to merit attention in this place. 

 Manley first points out that Landolt, in his classical investiga- 

 tions, seems to have omitted taking precautions against certain 



* Sitzungsber. d. Heidelb. Akad. d. Wiss., Abth. 24, 1911, p. 19. 



