188 METAL-AMMONIA COMPOUNDS.eter. If some undecomposed hexammine remains, the pressure
will be much greater. Weigh the tube and its contents as a further
proof that the change has been completed.- /3-Dlammlnedichlorocobalt, /3-[Co(NH 3 ) 2 Cl 2 ].
The unstable (3-diamminedichlorocobalt can be obtained by careful decom-
position of the hexamminecobaltous chloride (cf. Nos. 141 and 142) at a fairly-
high temperature, as the primary decomposition product.
Place about 2 g. of hexamminecobaltous chloride in the appara-
tus used in the preceding preparation. Weigh the substance taken
to 4 significant figures. Heat the contents of the test-tube to 72°
but in this case pump off the ammonia continuously until there is
no more of the undecomposed hexammine discernible with the
aid of a lens and the substance appears a pure light blue in color
(about 2 hours). From time to time, tap the test-tube and shake
it a little so that the entire powder is uniformly heated. Finally,
weigh the tube and its contents again, to prove that the decom-
position is complete.
Transformation of /3- into a-diamminedichlorocobalt. In order to
show, even more clearly, that the beta salt is less stable than the
alpha, and to illustrate the transformation, place a few milligrams
of each diammine in separate glass tubes of about 15 cm. length
and 6 mm. internal bore. Evacuate both tubes and seal them by
softening the glass with a flame and drawing out the glass. Sus-
pend both of the sealed tubes in a bath at 180° which can be done
conveniently if a little glass hook is made at the top of the tubes
when they are being sealed. After about an hour it will be found
that the blue diammine has become pink while the pink diammine
has remained unchanged.
The experiment succeeds even in open tubes but the change doesnot show as convincingly.
HYDRATES.
The hydrates formed by crystallization from aqueous solutions vary in
composition with the temperature and concentration of the solution. A
systematic determination of the hydrates which a compound can form, as
well as of the conditions under which they can exist, can be carried out in
the light of the principles of heterogeneous equilibrium.