The difference between these two latter substances was first pointed out by Cronstedt, and in 1778 C. Scheele prepared molybdic acid from the sulphide.
Molybdenum occurs in nature chiefly as the minerals molybdenite (MoS 2) and wulfenite (PbMo04), and more rarely as molybdic ochre (Moos) and ilsemannite; it also occurs in many iron ores.
In 1778 he proposed a new method of making calomel and powder of algaroth, and he got molybdic acid from mineral molybdaena nitens which he carefully distinguished from ordinary molybdena (plumbago or black lead of commerce).
Tungstic acid closely resembles molybdic acid in combining with phosphoric, arsenious, arsenic, boric, vanadic and silicic acids to form highly complex acids of which a great many salts exist.