1889 - 90 .] Dr J. Gibson on Action of Sodium Carbonates. 57 
the iron group by means of sodium carbonate and bromine, and was 
thereby led to investigate the action of these two reagents on solu- 
tions of nickel and cobalt salts. 
Green Cobalt Solution . — If sodium carbonate is added in large 
excess to a solution of a cobalfcous salt, on shaking the mixture 
with a sufficient quantity of bromine, the whole of the precipitated 
cobaltous carbonate dissolves, giving rise to a beautiful dark green 
solution. This solution is stable when preserved in closed vessels 
at ordinary temperatures. It decomposes on boiling with precipita- 
tion of cobaltic oxide. Caustic alkali produces rapid decomposition, 
cobaltic oxide being precipitated. The green colour is destroyed 
on acidifying with hydrochloric or sulphuric acid, but reappears on 
neutralising the acidified solutions with sodium carbonate. Acetic 
acid does not decolorise the green solution. 
Red Cobalt Solution . — If the green solution, prepared as above, 
is acidified with sulphurous acid, and the decolorised solution then 
rendered alkaline with sodium carbonate, a fine red-coloured solu- 
tion is produced. On shaking this in presence of air, it absorbs 
oxygen and becomes green. On standing, the colour goes back to 
red, but, on again shaking with air, becomes green. These changes 
of colour may be produced a number of times. After some time, 
or on adding alcohol, the red solution ceases to become green on 
shaking with air. 
The reaction of solutions of nickel salts with sodium carbonate 
and bromine are very complex. They vary in a remarkable 
manner, according to the temperature and concentration of the 
solutions employed and the relative proportion and order in which 
the reagents are added. 
If excess of sodium carbonate is added to a solution of nickel, 
the resulting mixture behaves differently on addition of bromine, 
according to the proportion of bromine added. If a large excess of 
bromine is added, part of the nickel goes into solution, part remains 
undissolved as pale green carbonate. On the other hand, if a smaller 
proportion of bromine is added, so as to leave excess of normal 
sodium carbonate, the nickel is rapidly and completely converted 
into peroxide. 
If bromine is added to a strong solution of sodium carbonate, and 
a small quantity of a dilute solution of a nickel salt is poured into 
