IN Engineering of September 13 there is an interesting article on the properties and applications of witherite (barium carbonate). It is stated in a handbook issued jointly by the Holmside and South Moor Collieries, Ltd., and the South Moor Collieries, and the Settlingstones Mines, Ltd., that witherite is found in economic quantities only in the northern part of England and that the mines producing it supply the world demands for the mineral. The material derives its name from that of Dr. W. Withering, a Birmingham physician and amateur geologist, who in 1784 when examining samples taken from an old lead mine at Alston Moor, on the borders of Cumberland and Northumberland, first recognized the mineral to be chemically distinct from barytes. Large quantities of witherite are used annually in the preparation of precipitated barium sulphate (permanent white) which is employed in the paper industry for the manufacture of highly glazed coated papers. It is also used in the printing ink and colour industries, in the manufacture of paints and as a filler in the rubber, linoleum and other industries. Among other engineering applications of witherite is the softening of water for boiler feed. It is specially useful when scale-forming and corrosive waters are encountered. Thus sodium and calcium sulphates are converted into the carbonates of these metals, with the precipitation of insoluble barium sulphate. Ground witherite mixed with wood charcoal, usually in the proportion of 40 per cent of the former and 80 per cent of the latter, has been used for many years as an energizer for carburizing compounds in the case-hardening industry. Considerable proportions of barium oxide, in some cases nearly 50 per cent by weight, enter into the composition of crown and flint optical glasses used for the production of lenses. Finely divided barium carbonate is also claimed to increase the resistance of cement to the action of sulphate-containing waters.