IV AUTHORS' PREFACE.combination, and thereby have returned to the older usage.
Among the early authors Thdnard in 1813 writes: "La methode,
que fai constamment suivie, consiste a proceder du simple au com-
pose, du connu a I'inconnu, a reunir dans un mime groupe tous les
corps analogues, et a les itudier d'abord d'une maniere generate et
ensuite d'une maniere particuliire." Gmelin in 1817, however,
took a different stand and in his "Handbuch" arranged the com-
pounds according to the elements, and thus introduced the sys-
tem of classification which has been followed by nearly all of his
successors. Even to-day Gmelin's reasons for departing from
the older method of treatment probably hold equally well as
regards elementary books for beginners; the older method scatters
the compounds of a single element in such a way that the student
fails to get a distinct, coherent picture. This book, however, is
intended primarily for those who have passed beyond the more
elementary stage in their study of chemistry, so that it does not
seem to us to be too daring to make the experiment as to how
well our modern, inorganic chemistry will fit into the older
framework. It seems as if thereby, aside from the old advan-
tage of a better comprehension of analogous methods of prep-
aration and analogous properties, there results a particularly
intimate amalgamation of experimental and theoretical chemistry,
for in this way we advance, as it were, from a "one compo-
nent system" to one of "several components." A similar return
to the older method of classification is to be found, for example,
in the second part of the Modern Chemistry by Sir W. Ramsey;
in the arrangement adopted by A. Werner and P. Pfeiffer in the
Inorganic Abstracts in R. Meyer's Jahrbuch der Chemie; and in
A. Werner's Neuere Anschauungen auf dem Gebiete der anor-
ganischen Chemie. This system was also outlined by one of us in
a lecture on Complex Compounds delivered in Gottingen in 1903-
1904.The method of arrangement chosen often separates prepara-
tions which are closely related to one another, as for example
where one is used as starting material for the formation of the
other; to show these relations the "Dependent Preparation"
is noted at the end of many of the procedures. In the last
chapter, which treats of compounds of the rarer elements, we
have departed from our chosen system of classification because