The existence of double salts, and the observations of L.
The insoluble salts are rose-red or violet in colour.
A large number of cobalt compounds are known, of which the empirical composition represents them as salts of cobalt to which one or more molecules of ammonia have been added.
In addition, certain inorganic salts, particularly certain compounds of potassium, are apparently necessary, but they seem to take no part in the chemical changes which take place.
The independence of the two is suggested by the fact that fungi can live, thrive and grow in nutritive media which contain carbohydrates together with certain salts of ammonia, but which are free from proteids.