The capacity of the test tube to the fust band from the bottom is meas

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VOL. 4. NO. 5

RAPIDDETERMINATION OF OXYGEN

IN

AIR

639

The capacity of the test tube to the fust band from the bottom is measured by pouring water into i t from a graduate. This is the volume of the remaining gas, principally nitrogen, which was left in the test tube. The tube is now filled to the second band and the new volume noted. This gives the total air capacity of the tube. The difference of these two volumes is the volume of oxygen in the given amount of air. This number divided by the total volume of air taken gives the percentage of oxygen in the air. Pyrogallic acid is a trihydric phenol with the formula C6H8(OH)sand is used in photography as a developer. It is a powerful reducing agent and precipitates gold, silver, and mercury from solutions of their salts, being itself oxidized to oxalic and acetic acids. Many dihydric phenols such as resorcinol and quinol show a corresponding behavior, but the monohydric compounds are much less readily oxidized. The fact that this determination can be made in a few minutes makes it attractive to the average student because it eliminates the necessity of correcting the volumes of the gases according to Charles' and Boyle's laws. These calculations are necessary in the usual phosphorus experiment which must stand for twenty-four hours. Perhaps it is well to postpone them until later in the year's work.

New Chemical Element Obtained in Pure Form. Rhenium, the chemical element whose discovery was recently announced by Doctors Walter and Ida Naddack, has now been obtained in pure form. The first discovery was based on the finding of the characteristic lines in the X-ray spectrum as detected by photographic plates, but now the Noddacks have succeeded in obtaining, after long and difficult refining processes, a small quantity of the substance itself. They describe i t as a black powder of high melting-point, that unites readily with a number of other elements. I n an athosphere of pure oxygen i t ignites, forming a white oxide. The quantity so far obtained is very minute, only two milligrams, or seven one-hundred-thousandths of an ounce, and the experimenters are now a t work to elaborate more of i t which will permit of exact quantitative chemical examination.-Science Sewice