78 PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



have no direct relation to the atomic weight, but depend on some other physical 

 property which obeys a similar law. In searching for such property it occurred to me 

 to try the atomic volume, and I found an almost precisely similar relation for these. 

 The densities of the alkalies are not so exactly known as those of other metals, and, 

 moreover, they ought to be compared at corresponding temperatures. If, however, 

 they are compared at about 10 to 15 C., and the values used which are given in 

 LANDOLT and BORNSTEIN'S tables, viz. : 



Li = "593 Na='9743 K = "875 Rb = T52 Cs = 1-88 

 the atomic volumes come out as follows : 



Li =11-81 =1x11-81 Rb = 56-05 =5xll'21 



Na = 23-606 = 2xll'80 Cs = 70'584 = 6x 1176 



K = 44-617 = 4x11-15 



As the density of Cs is taken near its melting point it is too small, and we should 

 expect a rather lower value for its atomic volume to compare with the others. 



To settle whether the atomic volumes are multiples of the same number requires a 

 more exact determination of densities. Mr. SWANN is at present investigating this 

 question. 



The values of /(/u 1) are 



Na . _ . . -2123(6) Kb . . . '2035(85) 



K . ' . . -2108(75) Cs . . . -1997 ? 



They indicate the same value for the ratio ('2120), but only by stretching Na and 

 Rb to the extreme limits. It is noticeable that the ratio as determined from the 

 most probable value continually decreases with increasing atomic weight. 



When these relations were first observed the [i for K used had been determined on 

 slightly different data, and the value of /A 1 was 4 ( '073984 + ), well within the 

 maximum limits above. In this case the series of values of /A 1 showed a superficial 

 agreement with the atomic volumes, but it was not possible to correlate them with 

 complete exactness. It was attempted to do so by adding a constant to ^ 1. It 

 was then found to give good agreement if this constant were about '014. In other 

 words, add "014 to the fractional part of ju and deduct it from the integral, i.e., 

 instead of writing /x = 1 +f, write p, = "986 + f ; then this fraction was proportional to 

 the atomic volume. It will be remembered that the difference found between the /t's 

 of the P and S series was about '487, so that the /x's of P and S are of the form. 

 "987 + f and '5 + f. This agreement for about "987 from two lines of agreement 

 strengthens the case for each. 



Again, if the values of a/f (/x, = '986 + f) be calculated, there results 



Na . . . -1951 Rb . . . -1951 



K -1975+ Cs -1937 + 



