Tungsten Trioxide: Wolframite Fused with Calcium Chloride (Wöhler)

Wolframite is iron and manganese tungstate. Fused with calcium chloride, its tungsten becomes calcium tungstate, which stays behind when the melt is leached with water. Nitric acid then turns it into a yellow precipitate, and heating that leaves tungsten trioxide, a canary-yellow powder. Source: Wöhler's method as given in Roscoe and Schorlemmer, A Treatise on Chemistry, vol. II part 2 (1923). It gives the ratio and the hour, not temperatures or the acid's strength. The 50 g batch and the crucibles are ours. Nitric acid is a strong acid. Picture drawn by Youblob.