That many of the so-called mysterious collapses of furnaces in apparently clean boilers is due to the presence of oil is the contention of an English engineer. He maintains that if the surface of the furnace in a boiler for 200 pounds pressure is kept clean, the temperature of the metal will never reach the point at which the original tensile strength will be appreciably reduced, even under high rates of evaporation. If» however, the surface is simply rubbed over with an extremely thin coating of mineral oil, the temperature immediately rises to over 650° with a moderate evaporation. It, therefore, follows that if a mere coating of oil of inappreciable thickness raises the temperature of the metal beyond the limit of safety, an extremely thin scale or deposit containing a high percentage of oil will inevitably result in dangerous overheating. He accounts for the fact that practically no oil is ever present in the harmless looking deposit found on the crown of collapsed furnaces by the theory that the temperature of the plate has been so high as to drive off the oil by distillation, and maintains that if the deposit were scraped from other parts of the boiler it would never fail on analysis to afford a solution of such accidents as are termed mysterious by those who do not realize the dangerous effect of a slight coating of oil.-"Chicago Tribune."

There is much that is somewhat mysterious about the explosion of nitro powders, gun cotton and other high-grade explosives, but it is agreed by all careful observers that when nitro powder is surrounded by a medium such as air, water or rock, the explosive force is exerted equally in all directions, but manifests itself chiefly in the direction of the least resistance. That is, if a blast is formed in a drill hole the gases formed by the explosion in their efforts to escape, will tear away a portion of the rock surrounding the drill hole. When dynamite is placed on top of a rock it will shatter the rock if it be not too large. If the same amount of powder is placed under the rock and in contact with it, it will also shatter the rock, showing that the explosive force is exerted in an upward as well as in a downward direction. The impression that many have that the explosive force of nitro - glycerine and dynamite is downward only, is erroneous.