The oxidation of metals is equally curious, and the length of time necessary for the formation of an infinitesimal coating of oxide is less than the one-thousandth of a second. This fact may be readily proved: a clean surface of steel, free from oxide, when brought in contact with mercury (quicksilver) will amalgamate, but if the least oxide be upon the surface no such effect will take place. Prepare a trough containing quicksilver, and place a bar of steel above it, and within one inch or less of the surface of the quicksilver--break this bar with a smart blow from a hammer, so that the blow which breaks it shall at the same time force the broken ends into the quicksilver, and although the time occupied by the ends in passing through one inch of atmosphere before reaching the surface of the quicksilver will be immeasurably short, still they will be so oxidized as not to amalgamate with the mercury; if, however, the bar of steel be confined at its ends below the surface of the quicksilver, and then be broken _upwards_, by a lever applied to its centre, the ends of the broken bar will be beautifully amalgamated before reaching the atmosphere above. The reason for the success of the last named experiment is doubtless due to the absence of oxide of iron, when broken beneath the surface of the mercury. J. J. MAPES. * * * * * New Weigh-lock at Albany.--A writer in the _Courier and Enquirer_ gives a description of the great weigh-lock that has just been erected at Albany, for the purpose of ascertaining the tonnage of canal boats. Heretofore long and vexatious delays have been the result, while now, a boat is brought into the lock, and in a time which would have scarcely sufficed in other days to have ascertained the weight of a small parcel, the unerring register on the beam, has registered its weight, and the record is on the books of the office. The weigh-lock is directly on the side of, and attached to the large canal, and is adapted to the use of such boats as shall hereafter be built, when the locks throughout the entire length of the canal shall be of the uniform enlarged size. * * * * * Daguerreotyping in London.--In a recent letter from J. E. Mayall, dated London, February 11th, he writes in his postscript:--"While I write this letter we have the gas lighted in the streets--1 o'clock P.M., and I write by gas-light." We must confess that the Daguerreotypists are in the "Fog" enough in this country, but if "Old Sol" should get blocked up at that early hour, we don't know what would become of our "Foggy" Daguerreotypists here. * * * * * The ground side of the "Ground Glass" should face the lenses. * * * * * Mercury baths should always be kept covered with some porous wood, in order that the mercurial vapors cannot escape in the room.