DOUBLE SALTS 159 
it possible to refer back the so-called ‘molecular compounds’ 
to actual linkings between quite definite atoms.” An exami- 
nation of the formule of the double salts dealt with in the 
course of this paper, will show that the majority of them support 
Werner’s hypothesis; thus, for the double chloride of copper, 
the double sulphates of the astrakanite type, the co-ordination 
number is six. But at the same time there are undoubted 
exceptions, such as FeCl,.3CsCl.H,O, for which the co- 
ordination number would be seven; CuCl,. LiCl. 2H.O, for 
which it would be five. It remains for future work to show 
how far these and other exceptions can be accounted for, and 
how far the hypothesis will prove deductively fruitful. At 
the present time it certainly marks an interesting attempt at 
simplification. 
