consisted simply of a brick box fifteen feet long and seven feet wide and deep, with big carbon electrodes at the ends. Between them was packed a mixture of coke to supply the carbon, sand to supply the silicon, sawdust to make the mass porous and salt to make it fusible. [Illustration: The first American electric furnace, constructed by Robert Hare of Philadelphia. From "Chemistry in America," by Edgar Fahs Smith] The substance thus produced at Niagara Falls is known as "carborundum" south of the American-Canadian boundary and as "crystolon" north of this line, as "carbolon" by another firm, and as "silicon carbide" by chemists the world over. Since it is next to the diamond in hardness it takes off metal faster than emery (aluminum oxide), using less power and wasting less heat in futile fireworks. It is used for grindstones of all sizes, including those the dentist uses on your teeth. It has revolutionized shop-practice, for articles can be ground into shape better and quicker than they can be cut. What is more, the artificial abrasives do not injure the lungs of the operatives like sandstone. The output of artificial abrasives in the United States and Canada for 1917 was: Tons Value Silicon carbide 8,323 $1,074,152 Aluminum oxide 48,463 6,969,387 A new use for carborundum was found during the war when Uncle Sam assumed the role of Jove as "cloud-compeller." Acting on carborundum with chlorine--also, you remember, a product of electrical dissolution--the chlorine displaces the carbon, forming silicon tetra-chloride (SiCl_{4}), a colorless liquid resembling chloroform. When this comes in contact with moist air it gives off thick, white fumes, for water decomposes it, giving a white powder (silicon hydroxide) and hydrochloric acid. If ammonia is present the acid will unite with it, giving further white fumes of the salt, ammonium chloride. So a mixture of two parts of silicon chloride with one part of dry ammonia was used in the war to produce smoke-screens for the concealment of the movements of troops, batteries and vessels or put in shells so the outlook could see where they burst and so get the range. Titanium tetra-chloride, a similar substance, proved 50 per cent. better than silicon, but phosphorus--which also we get from the electric furnace--was the most effective mistifier of all.