430 TRANSACTIONS OF SECTION B. 
periodic functions of the atomic weights must be abandoned in favour of 
some more comprehensive scheme. From the chemist’s point of view, it is 
impossible to abandon the guiding principle underlying the arrangement in 
family groups, which dates back to Dumas; perhaps insufficient attention 
has been paid in the past to the maintenance of this principle. 
Taking this principle into account it is impossible to arrange a long 
series of elements such as the rare earths continuously in order of atomic 
weight, as they would be brought into every family in the table by such a 
procedure ; the difficulty has been got over by Brauner, who has proposed 
to arrange a large number of the rare earths in a single vertical series under 
barium. Biltz has made a similar proposal. 
The principle had been advocated by me previously in an article written 
for the ‘ Encyclopedia Britannica.’ * 
In the arrangement I have proposed, it is not only assumed that there 
may be as many as sixteen vertical series of elements of which the elements 
from hydrogen to oxygen are initial terms, some series being at present un- 
represented, it is also suggested that groups of elements occur in perhaps 
four of these series, numbers 4, 8, 12 and 16, the largest being that of the 
so-called rare earths in series 8. 
The principle which is assumed to be in operation is that which is so 
clearly manifest in the case of hydrocarbons: successive vertical series of 
elements correspond to successive isologous series of homologous hydro- 
carbons. In the case of the hydrocarbons, the passage from one isologous 
series to another often takes place from a term several places removed from 
the origin of the series—for example, from benzene, C,H,, which may be re- 
garded as primarily a derivative of hexane, to naphthalene, C,,H,, which 
is not an immediate derivative of benzene but of butylbenzene. It is conceiv- 
able that at the genesis of the elements a process was at work corresponding 
to that by which a hydrocarbon such as naphthalene is derived from benzene 
and by which the former then serves in turn as the point of departure for 
more complex hydrocarbons of other series. There is no reason, from this 
point of view, why progression should not take place along a particular 
line and that terms should exist in a series through which this line passes 
but below it—for example, that antimony and iodine may bear a direct linear 
relationship but that tellurium, instead of being the element in the pro- 
gression series in the oxygen group, is a homologue of greater weight. The 
same view may be taken of selenium. In this way, it would be possible to 
maintain selenium and tellurium in the oxygen-sulphur series, from which 
they cannot well be separated, whilst retaining Mendelejeff’s conception of a 
genetic relationship along the series. The only departure involved is in 
assuming that instead of forming a single linear series ascending regularly 
in spiral progression—a series which can, as it were, be strung on a single 
spirally wound cord—the elements closely simulate a series of homologous 
dsologous hydrocarbons. From this point of view, it is easy also to under, 
stand that some vertical series are unrepresented. 
In discussing the chief attributes of the elements none is so difficult to 
deal with as that of valency, using the term in the broadest possible sense, 
not merely as indicative of the number of units of affinity but as including 
the, at present, all but incomprehensible problems of residual affinity and 
elementary character. I discussed the subject somewhat fully in my former 
address, dwelling especially on the properties of negative elements and the 
power such elements have of acting as linking agents; this view has met. 
with ample confirmation in the interval and will, I believe, be found to be 
of wide application in the future. I have already referred to the manner 
in which_it is exemplified by silica. 
1 Cf, Roy. Soc. Proc., 1902, vol. lxx. pp. 86-94, 
