THE ACTION OF tIEAT IN VACUO ON METALS.*: By T. A. Emsox.
In file course of my experiments on electric lighting I have devel-,ped some striking phenomena arising from the heating of metals by flames and by the electric current, especially wires of platinum, anc[ platinum alloyed with iridium. These experiments are in progress.
The first fact observed was that platinum lost weight when heatect in a flame of hydrogen, that the metal colored the flame green, an& flint these two results continued until the whole of' the platinum in contact with the fame had disappeared. A platinum wire four-thousandths, ,)f an inch in dianieter, and weighing 306 m.grms., was bunched together and suspended in a hydrogen flame. It lost weight at the rate of a fraction less than 1 re.grin, per hour as long as it was suspende& in the flame. When a platinum wire is stretched between two clamping posts, and arranged to pass through a hydrogen flame, it is colored, a light green; but when the temperature of the wire is raised above that of the flame, by passing a current through it, the flame is colored a deep green. To ascertain the diminution in the weight of a platinum wire when heated by the electric current, I placed between two clamping posts a wire five-thousandths of an inch in diameter, and weighing 266 re.grins. This wire, after it was brought to incandescence for twenty minutes by the current, lost I m.grm. The same wire was then raised to incandescence; ibr twenty minutes it gave a loss of 3 re.grins,. Afterward it was kept incandescent ibr one hour and ten minutes~. at which time it weighed 258 re.grins., a total loss of 8 re.grins, Another wire, weighing 343 re.grins., was kept moderately incandescent for nine consecutive hours, after which it weighed 301 m.grms., showing a total loss of 42 re.grins. A platinum wire twenty-thousandths ,f an inch in diameter was wound in the form of aspiral one-eighth of,' an inch in diameter and one-half an inch in length. The two ends of' the spiral were secured to clamping posts, and the whole, apparatu s was. covered with a glass shade 2.} inches in diameter and 3 inches high.. Upon bringing the spiral to incandescence for twenty minutes that part ~A Paper read before the American Association for the Advancement of Science ;; Saratoga Meeting.