Didymium
a metallic triad element, symbol Di", atomic weight 144. It occurs along with cerium and lanthanum in the mineral cerite. It is separated from cerium by igniting the oxalate, and treating the resulting oxides with very dilute nitric acid, which does not dissolve the cerium oxide. The filtered solution is mixed with sulphuric acid, concentrated by evaporation, and then a hot solution of potassium sulphate is added, which precipitates the DIE lanthanum and didymium as double sulphates.
Didymium can from lanthanum by precipitating half be separated the oxide with ammonia, and leaving the precipitate in contact with the solution; being the stronger base, then passes into solution in predominant quantity. By repeating the process, the ain dissolved and precipioxides being again tated, the didymium oxide is obtained nearly pure.
Didymium is a white metal with a tinge of yellow; specific gravity, 6.5. It tarnishes in dry air; it burns with great brilliancy when thrown into a flame. Its oxide, Di₂O₃, is a dirty bluish color; the nitrate is obtained in large violet crystals by dissolving the oxide in nitric acid.
The sulphate, Di2 (SO₂): 6H₂O, forms rose-red crystals.
The oxalate is a crystalline powder. trum of a solution of a salt of didymium contains characteristic dark bands. der. The spec- In botany, the word is applied to a genus of gasteromycetous fungi, consistof gasteromycetous fungi, consisting of minute ing of minute plants growing upon etc., distinguished by its guished by its double peridium.