Page:Popular Science Monthly Volume 2.djvu/524

506 and solidification at existing mean atmospheric temperature, of basic and acid slags analogous to melted rocks. Mallet thus finds that less than one-fourth of the heat annually lost by our globe is sufficient to account for its total annual vulcanicity. He then shows the accordance of his views with sundry facts of vulcanology and seismology. Finally, he accounts, on his theory, for the elevations on our moon's surface, and the evidence there of former volcanic energy, on a grander scale than on our planet.

The Vibrations produced by Various Explosives.—It is known that the instantaneous combustion of an explosive body is brought about by vibrations, independently of the agency of heat. An interesting inquiry here arises, whether these vibrations are identical for all explosives; and whether we can determine in advance the action of one explosive upon another. Two French savants, MM. Champion and Pellet, have investigated this subject, and the following is an account of their experiments: First, they set up an apparatus with eight gas-burners, to give "singing" flames, answering to the eight notes of the gamut. For the first experiment an anvil was placed at a distance of sixteen feet from this apparatus, and on it they placed in succession 0.03 grammes of iodide of nitrogen and fulminate of mercury, both enclosed in sacks of gold-beater's skin. The iodide, on being exploded, had no effect on the flames, while the fulminate caused the following flames to play: la, do, mi, fa, and sol. The conclusion is, that the vibrations produced by the two agents differ mutually, and further, that the vibrations caused by the fulminate act on some notes, passing over the others. In the second experiment the flame-apparatus and the anvil were placed twelve feet apart. It was now found that the iodide acted on the higher notes, whereas the fulminate affected the entire scale. But. if now we make each charge two decigrammes, and bring the anvil very close to the apparatus, the whole gamut will respond to both explosions. The third experiment was a repetition of the foregoing two, with this exception, that nitro-glycerine was substituted for iodide of nitrogen. The result did not show any difference between these two agents in their action on the flames; and yet it is known that there is a difference between their respective vibrations; for the fulminate will explode compressed gun-cotton, but nitro-glycerine will not, under identical conditions. No doubt, if a more perfect flame-apparatus, with a series of low notes, had been employed, a difference would have been manifested in the course of the experiment.

Economy of Fuel.—A self-feeding furnace is now in use in several English manufacturing towns, which is said to effect a great economy in the consumption of coal, besides possessing the additional advantages of burning all the refuse and completely consuming the smoke. A small and uniform amount of fuel, just enough to replace that consumed, is being constantly added to the fire, which is supplied with exactly as much air as is required to carry on the combustion in the most economical and effective manner. The apparatus is known as Vicar's Furnace, and is readily fitted to any kind of boiler, and to reverberatory furnaces of all descriptions.

Ammonia in Snow-water.—Dr. Vogel has an article on ammonia in snow-water in the Sitzungsberichte der mathematico-physikalischen Classe, of the Munich Academy of Sciences. The method employed by him is that of Schlösing, for estimating the amount of ammonia in arable soil. The results obtained were as follows, one litre (2.113 pints) being the unit: Freshly fallen snow, caught in a porcelain basin, at zero, gave 0.003 grammes; at -3° gave 0.002; at from -9° to -15° gave no ammonia. Water from snow which had stood 24 hours on a piece of manured garden-ground, contained 0.012 grammes; from snow which had stood on a meadow for 24 hours, 0.009 grammes; from a zinc roof, 0.004 grammes. Dr. Vogel observes that the quantity of ammonia in snow depends on a variety of conditions, and that, since snow, owing to its porosity, absorbs ammonia (and the same is true of snow-water), it is necessary to melt it in closed vessels. The amount of ammonia in snow is also dependent on the temperature at which it falls. At a rather