Chemistry and Physics. 323 



problems are included. The questions and problems have been 

 taken from the most recent examination papers and text-books. 

 There is a great number of them, and a student who could answer 

 them all correctly would certainly have a thorough knowledge of 

 the subject. There are no explanations, and no answers are 

 given. h. l. w. 



8. Spectrum of Ionium. — The spectrum of a mixture of the 

 pure oxides of ionium and thorium has been recently investigated 

 by A. S. Russell and R. Rossi. The percentage of ionium oxide in 

 the preparation can be calculated from the period of ionium taken 

 in conjunction with the number of a-particles emitted by one gram 

 of the substance per second. Soddy has found that, on certain 

 assumptions, the period must be at least 100,000 years. Also, 

 Geiger has found the above mentioned number of a-particles to 

 be lo 8 . From these data it follows that the per cent ol ionium 

 oxide in the mixture used cannot be less than 1(5. 



The investigators photographed the arc spectrum of the mix- 

 ture between the wave-lengths A— 3800 and A=5000 A. U. Two 

 gratings were used successively, the one having a radius of curv- 

 ature of about 3 feet, and the other about 21*5 feet. Not a single 

 new line was found, although, under similar experimental con- 

 ditions, the presence of one per cent of Ce0 2 could be easily 

 detected, and one per cent of XJ 3 8 was just at the limit of detect- 

 ability. A like negative result for the spectrum of ionium has 

 also been found by Exner and Haschek, who investigated both 

 the ultra-violet and visible regions of the spectrum. 



The failure to obtain the lines of ionium may be explained on 

 the ground that the period of ionium is much less than 100,000 

 years, as assumed above. In this event, at least one new radio- 

 active body precedes ionium in the disintegration series between 

 uranium X and radium. If such a substance exists it cannot emit 

 a- rays (since all of these rays have been accounted for), but it 

 may be either rayless or it may emit soft /2-rays only. Hence, 

 the percentage of ionium oxide present in the mixture may have 

 been greatly overestimated ; in other words, the amount of ionium 

 in the preparation may have been too small to be detected spec- 

 troscopically under the experimental conditions. On the other 

 hand, it is thinkable that ionium has no radiation in the region 

 investigated or, possibly, ionium and thorium have identical 

 spectra in the ultra-violet and visible portions of the spectrum. 

 In any event, the question is still an open one, and the absence of 

 a detectable spectrum is very interesting and suggestive. — Proc. 

 Boy. Soc, No. A, 598, p. 478. h. s. u. 



9. The Excitation of y-Bays by a- Rays. — The recent investi- 

 gations of J. Chadwick have definitely established, for the first 

 time, the fact that y-rays may be excited when a-rays impinge on 

 matter. The a-rays employed were emitted by radium emanation 

 together with its active deposit. Since the radio-active material 

 was sealed up in a glass tube with very thin walls special care 

 had to be taken to avoid errors which might arise from the exci- 



