DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
45 
numbers must be due to chance, for they would he altered hy the slight alteration in 
density as measured in different physical conditions. We should be prepared to 
expect a considerable difference in the numher for Hg, as it is so far above its melting- 
point. Without, however, giving any special weight to the exactness of the 
agreement, it yet affords strong evidence for the dependence of the p-sequence on the 
real atomic volume in the manner indicated. If Eu behaves in an analogous way we 
should expect it to be proportional to 7v, i.e., '244083 = '002720 xfv or v = 12'8G, 
whence, taking the atomic weight of Eu to he 152'03,'*' the density of Eu at ordinary 
temperatures should be about 11'86, ^.e., intermediate between those of Cd and Hg, 
as is to be expected. 
In the case of the alkaline earths we have to consider the two forms of the 
sequence—(l) that involving and (2) that in which multiples of A 2 are added to 
give the first spectral line of the series. Also, in the first form the question arises 
whether the quantity to be discussed should he the denominator of VS(l) or with /3 
left out. In fact, if the atomic volume term is the factor ^ wlien the denominator is 
thrown into a form containing a term (l — ■21520??i“^), tlien the quantity to be 
considered would be the latter, assuming the results given in (p. 4l). For comparison 
both cases are treated, 1 («) and 1 {h), in the table below. The fourtli line gives the 
numbers for Case (2). As in the Zn sub-group it will be found that multiples of 
V enter. 
Mg (8v). 
Ca (7v). 
Sr (6v). 
Ba (6v). 
Ra {xv). 
Density . 
1 (a) . . . . 
1 (/*)... . 
2 
1-72 
•002783 
•002710 
•002764 
1-57 
•002731 
•002625 
•002693 
2-54 
•002649 
•002570 
•002623 
3-77 
•002862 
1 
•002782 
1 -023; 
The densities used in calculating are the means of those given by Landolt and 
Bornstein ; the values for Ca and Sr are not very accurate. In the case of Sr the 
density is given as between 2’50 and 2'58 ; tlie latter would alter the numbers above 
for Sr to '002604 in Case (2) and '002690 in Case 1 (a) The number for Ba is 
calculated on the doubtful basis of (p. 39), and it is necessary to take a multiple of 
6 r. If Saunders’ allocation be correct the value of S ( 00 ) is very much less, and the 
value of the denominator of VS (l) is close to 1'492765. In this case, if a multiple 5v 
is taken, the ratio is '002705. Moreover, this ratio is in analogy with the others, and, 
so far, it adds weight to Saunders’ allocation. It is quite possible that the value of 
SrS (CO) is too high, which would result in too small a value for the ratio. The 
numhers, however, are sufficiently close for all these elements to afford additional 
* Jantsch, ‘C. R.,’ 1908, vol. 146, p. 473. 
