DINITRITOTETBAMMINECOBALTIC SALTS. 181
then with pure alcohol, and dry the product in a desiccator. The
yield is variable.
Reactions. A cold solution of croceochloride on being treated
with potassium chromate gives a yellow precipitate of short,
blunt crystals; with potassium dichromate there appears (but
only after shaking some time) a deposit of short leaflets which are
frequently grouped together in the form of stars (microscope).
On being treated with nitric acid, yellow, feathery crystals of the
difficultly-soluble nitrate are formed (0.25 g. of the latter dissolve
in 100 c.c. of water at the room temperature).- Comparison of the Isomerlc Dinitrltotetramminecobaltic Salts.
The difference between the flavo and croceo salts, in both of which the
complex has the same empirical formula, [Co (1013)4X2], can be explained
according to Werner's theory by assuming that the substituents in the "inner
sphere" are arranged differently in space. It is evident that if the con-
stituents of the complex are placed around the central cobalt atom some-
what as the corners around the middle point of an octahedron, there are two
possible arrangements; either the two constituents,. X, which are different
from the other four, are arranged opposite to one another and are connected
by the hypothetical axis of the octahedron (trans-position), or they are situ-
ated side by side and are joined by one edge of the octahedron (cis-position).
If the corners of the octahedron are numbered from one to six, as shown below,
then the first arrangement may be designated as 1 • 6 and the latter as 1 • 2.
I X X
5> I 7 2 KH3/ 7 KH» NHj/ 1 7X
/Co / / Co / / Co /6 X NH 3
1, 6: trans-position 1, 2: cis-positionThe usefulness of the above conception of isomerism is shown, among
other ways, by the fact that it does not allow isomers to exist of the com-
plexes in which only one of the substituents is different from the others;
in reality no such isomers have been observed. It has been found that the
crooeo salts correspond to the trans arrangement, the flavo salts to the cis
arrangement. The praseo salts belong to the trans series.
It is of fundamental importance with respect to Werner's conception of the
structure of complex cobalt compounds, that it has been found possible to
prepare isomers capable of rotating the plane of polarized light in opposite