1904-5.] Mr Cameron on the Constitution of Complex Salts. 731 
complex halides with each other and with the “ double cyanides.” 
Weinland and Koppen * have shown that by the conception of the 
replacement of one atom of oxygen by two of fluorine, and by the 
comparison of the complex fluorides of bivalent metals with the 
aluminites and ferrites, perfectly consistent formulae can he assigned 
to the former, and Locke f has pointed out that “all the sesqui- 
oxides which form alums yield soluble double potassium cyanides.” 
But no one, so far as I have been able to ascertain, has recognised 
the great structural similarity in the constitution of all these 
complex salts ; no one has shown that to the derivatives of the 
sesquioxides, with few exceptions, can he ascribed definite con- 
stitutions on the basis of a few simple types ; and no one has 
pointed out the striking parallelism between the complex salts of 
various acids usually described as monobasic, and those derived 
from dibasic acids. 
The structural similarity referred to is best shown by the table 
on the opposite page. This table is by no means exhaustive 
either with regard to acids or to trivalent metals, but has been so 
chosen as to include most of the important series of compounds, 
and instances of every type. I have endeavoured to make it as 
complete as possible with regard to the acids and metals contained, 
and to give correct references to the chemists who have recently 
prepared and investigated these compounds. It is highly probable 
that once the necessary conditions have been found most of the 
vacant spaces in this table will be filled. 
A comparison of the chromium derivatives will best show the 
relationship between the different complex acid groups, while a 
glance at the complex chlorides, fluorides, and oxalates will best 
illustrate the close correspondence which exists between them. 
A few of the compounds included may be mentioned. Thus, in 
the first column are the hydroxides themselves, the chromites, 
ferrites, aluminites, arsenites, etc. ; in the second are found copper 
pyrites, and the thio-salts of arsenic, antimony, and bismuth ; the 
“ anhydrous alums ” form the complex sulphates of type B. 2. 
The formulae ascribed to the complex halides, cyanides, etc. 
may be best understood by considering the compounds of the 
* Zeit.fur anorg. Chem., 22, p. 275. 
t Amer. Chem. J., 20, p. 589. 
