Page:Popular Science Monthly Volume 35.djvu/617

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THE SURFACE TENSION OF LIQUIDS.

In a third experiment a strip of thin, unglazed paper, say six inches and three quarters long by an inch and a half wide, is folded so as to form a box or trough, as represented in the lower part of Fig. 3. Set the box on a table, moisten the inner faces with a wet brush, and pour in water from an inch or two above. The tension of the liquid surface will at once bring the long sides of the box together, and the vessel will thus shut upon itself.

PSM V35 D617 Adherence example by the concave surface tension of water.jpg
Fig. 1.—Adherence of one Pencil to another by the Tension of Concave Surfaces of Water.

Again, take a cylindrical cork of about wine-bottle size; fix in the center of one end a fine iron wire terminating in a hook or pan to hold ballast. In the other end fix a ring about four inches in diameter, lifted on branching supports as in Fig. 4. Plunge the apparatus into a vessel containing a suitable depth of water. With a proper weight of ballast, the cork will assume a vertical position, and will rise only to a certain distance above the level of the water. But if the whole is pushed down into the liquid and left there, the ring will not again clear itself from the water; it will only rise a little above its level, producing a double concave meniscus. In this case the effect of superficial tension is to give rise to a downward resultant sufficient to counterbalance the increase of the upward thrust. If the ballast is managed so that the excess of this resultant is but slight, on the application of ether by a wad or sponge, the effect of which will be to diminish the superficial tension of the water, the ring will rise from the liquid and the apparatus assume its original position.

In a fifth experiment a square frame of wire is dipped into a