Hunting Tungstic Acid

Scheele mentioned in a letter of 1780 to professor Torbern Bergman in Uppsala that he was engaged in investigating the mineral tungsten. He chose, with good intuition, an investigation technique different from what he had used when he was on the track of molybdic acid. It is true that the two metals are chemically similar but they are bound in quite different ways in their minerals. In today s terms  

In 1781 Scheele pubHshed his results for the mineral tungsten in the Transactions of the Academy. The paper had the simple title The components of tungsten [26.1]. 

Scheele had used two methods to isolate the unknown acid . In one the decomposition occurred with melting. The powdered mineral was mixed with potassium carbonate and the mixture was melted in an iron crucible. The solidified melt was leached in warm water. After filtering the filtrate was acidified with nitric acid. The new unknown acid was precipitated. It was again melted with potassimn carbonate and the procedure was repeated. A pure white tungstic acid was obtained. 

The other method was wet chemical . The finely powdered mineral was treated with nitric acid. It was attacked and some of it was dissolved. The solution contained calcium nitrate. The insoluble residue was partly not attacked tungsten mineral and partly a yellow precipitate, formed in the reaction. Scheele thought that this was the anhydride of the tungstic acid. The yellow precipitate could be dissolved in ammonia. From this solution tungstic acid was precipitated with diluted nitric acid 

Now the situation with molybdic acid was repeated. Scheele had prepared the add of a new metal but he was incapable of taking the last step the final isolation of the element. His pharmacy did not have furnaces strong enough. This time he did not in- 

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