In the milling of tungsten ores, the tendency in this country is to get away from the uneconomic method of making concentrates very high in tungsten trioxide (carrying more than 60 per cent. WO₃). Few operators really know what the heads run, and the determination of losses is mere guesswork. Some of the most careful operators in the Boulder field before closing down at the beginning of 1919 were making a high-grade product carrying nearer 50 per cent. than 60 per cent. tungsten trioxide, and a lower grade product carrying about 20 per cent. tungsten trioxide, not attempting to raise its tenor. This practice cuts down the losses largely. When the great shortage of tungsten ore came in 1916, users were compelled to take lower grade concentrates, and some improved their metallurgy accordingly. This change has made the sale of 50 per cent. concentrates easier. Even in England, 60 to 65 per cent. ores were accepted where formerly a content of 67.5 per cent. or 70 per cent. WO₃ was demanded. Formerly scheelite sold 50 cents per unit below other tungsten minerals, even though freer from bothersome impurities, but with the graduation from rule-of-thumb methods to more thoughtful, careful and scientific practice, it came to command a premium. Huebnerite seems to be still sold with and as “wolfram” in England, but in this country it must be sold according to its composition, for to most metallurgists the manganese is undesirable, though at least one firm now makes ferrotungsten from huebnerite without prejudice or difficulty. This growth in knowledge and technique has caused the price of the tungsten minerals to rank about as follows in the order named: Scheelite, ferberite, wolframite and huebnerite. This applies to tungsten used in the manufacture of tungsten and ferrotungsten for steel making. Scheelite is not wanted in this country for making filaments.