We are all familiar with this reaction now, for it is acetylene that gives the dazzling light of the automobiles and of the automatic signal buoys of the seacoast. When burned with pure oxygen instead of air it gives the hottest of chemical flames, hotter even than the oxy-hydrogen blowpipe. For although a given weight of hydrogen will give off more heat when it burns than carbon will, yet acetylene will give off more heat than either of its elements or both of them when they are separate. This is because acetylene has stored up heat in its formation instead of giving it off as in most reactions, or to put it in chemical language, acetylene is an endothermic compound. It has required energy to bring the H and the C together, therefore it does not require energy to separate them, but, on the contrary, energy is released when they are separated. That is to say, acetylene is explosive not only when mixed with air as coal gas is but by itself. Under a suitable impulse acetylene will break up into its original carbon and hydrogen with great violence. It explodes with twice as much force without air as ordinary coal gas with air. It forms an explosive compound with copper, so it has to be kept out of contact with brass tubes and stopcocks. But compressed in steel cylinders and dissolved in acetone, it is safe and commonly used for welding and melting. It is a marvelous though not an unusual sight on city streets to see a man with blue glasses on cutting down through a steel rail with an oxy-acetylene blowpipe as easily as a carpenter saws off a board. With such a flame he can carve out a pattern in a steel plate in a way that reminds me of the days when I used to make brackets with a scroll saw out of cigar boxes. The torch will travel through a steel plate an inch or two thick at a rate of six to ten inches a minute. [Illustration: Courtesy of the Carborundum Company, Niagara Falls MAKING ALOXITE IN THE ELECTRIC FURNACES BY FUSING COKE AND BAUXITE In the background are the circular furnaces. In the foreground are the fused masses of the product] [Illustration: Courtesy of the Carborundum Co., Niagara Falls A BLOCK OF CARBORUNDUM CRYSTALS] [Illustration: Courtesy of the Carborundum Co., Niagara Falls MAKING CARBORUNDUM IN THE ELECTRIC FURNACE At the end may be seen the attachments for the wires carrying the electric current and on the side the flames from the burning carbon.] The temperatures attainable with various fuels in the compound blowpipe are said to be: Acetylene with oxygen 7878 deg. F. Hydrogen with oxygen 6785 deg. F. Coal gas with oxygen 6575 deg. F. Gasoline with oxygen 5788 deg. F.