334: Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Spectrum of the Residual Glow. — Crookes has ex- 

 amined the spectrum of the residual phosphorescent glow obtained 

 when the rarer earths are illuminated by the electric spark in a 

 modified form of Becquerel's phosphoroscope. The glow is ob- 

 served through apertures in a revolving disk, twelve in number, 

 symmetrically placed. On the axis of the disk is a brass cylinder, 

 having twelve teeth at one end. An adjustable spring presses on 

 the teeth, a second spring upon the smooth surface of the cylin- 

 der, these springs completing the battery circuit through the 

 primary of an induction coil. By suitably adjusting the former, 

 the spark may be made to take place at the instant when the 

 substance under examination is visible through the aperture in 

 the disk, or to precede it by a very short interval easily calcu- 

 lated. The relative length of the makes and breaks is adjusted 

 by moving the spring to or from the bases of the teeth. Much 

 lower vacua are necessary, since the residual gas has no phospho- 

 rescent spectrum. The phosphorescent bands in the spectrum of 

 pure yttria do not appear at the same speed of rotation. The 

 first to appear is the greenish-blue band G/3, then the deep blue 

 Ga, the citron G3 and the deep red G<§ ; the last at a duration 

 of 0-00175 second. At 0-00125 second Go" and G/5 are equally 

 bright and G77 just visible ; and at -000875 second all the bauds 

 are seen ■of their usual brightness. The author has observed that 

 on adding strontia to a mixture of yttria and samaria and on view- 

 ing it in the above phosphoroscope with the wheel rotating rap- 

 idly, the line Q3 is completely suppressed and the spectrum is 

 identical with that of Marignac's Ya. Alumina, giving the crim- 

 son line has a very persistant residual glow. Antimony oxide 

 mixed with lime in the proportion of five per cent phosphoresces 

 white with a broad space in the yellow. In the phosphoroscope 

 the glow is green and very strong, the red and orange being ob- 

 literated. Chromium oxide with lime in the same proportion, 

 gives a pale red phosphorescence, the red and orange being cut 

 off in the phosphoroscope. Diamonds glowing pale blue have the 

 longest residual glow, those glowing yellow coming next; those 

 phosphorescing red have no residual glow. Zinc sulphide (Sidot's 

 hexagonal blende), phosphoresces brilliantly even in a very low 

 vacuum, with a green light. As the exhaustion is increased the 

 edges of the crystals become blue, the two colors finally being 

 equally bright. In the phosphoroscope, however, the blue is visi- 

 ble only at a high speed while the green lasts for an hour or more. 

 The curious fact is noted that the spark spectrum of old yttrium 

 and of the higher and lower fractions obtained froni it are per- 

 fectly identical, though the phosphorescent spectra and chemical 

 properties of the three are markedly different ; and the author 



