divisions, and it was combined with a spectral monochromator. By 
comparison with the spectra of hydrogen and of the metals: sodium 
lithium, ecaleium and thallium, the micrometerscrew of the mono- 
chromator was calibrated beforehand. As luminous source a NERNST- 
lamp was used; the tubes had in all experiments a length of 20 cm. 
The wave-lengths are expressed in Anastrom-units (A. U.); the 
molar rotation {m| was caleulated from the expression: 
|mj| =a 7 
in which « is the observed rotation, / the length of the tube in 
em., and V is the volume of the solution in cm”, containing just 
one grammolecule of the anhydrous salt. With the purpose of 
avoiding too big numbers especially in the graphical representation 
(fig. 2), [m|.10—!'-is everywhere given. 
~The exact determination of the rotation-dispersion was in all cases 
limited by the strong absorption of the redbrown or yellow solutions; 
for the same reason too concentrated solutions could not be studied. 
The exactness of these determinations is of course not unappreciably 
less than in the case of colourless solutions; however a schematic 
and fairly true expression of the dispersion was beyond doubt 
obtained in this way. 
It was observed moreover, how in the immediate neighbourhood 
of an absorptionline, the rotation reaches a maximum value, and 
then decreases very vapidly, in some cases the algebraic sign of 
the rotation being even reversed. Probably the remarkable pheno- 
mena of abnormal rotation-dispersion, observed by WeRNER in some 
cases, among others with the trioxalo-derivatives, etc, will prove 
to be in an analogous connection with the absorption-lines present 
in the spectra of the solutions of these salts. 
The molecular rotation-dispersion of the luteo-triethylenediamine- 
cobalti-cation has an enormous value: for the sake of comparison 
the corresponding curve for saccharose is reproduced in fig. 2 on 
the same scale. 
The temperature of the studied solutions varied from 15°—20° C.; 
special experiments at 10°, 18°, 54° and 98° showed us that the 
rotation does not change very appreciably with the temperature. 
The results of the measurements are reproduced in the following 
tables; all rotations. are calculated with respect to one gram-molecwe 
of the anhydrous salts. 
