THE SURFACE TENSION OF LIQUIDS. 



593 



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. 



Fig. 1.— Adherence of one Pencil to another by the Tension of Concate 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 in- 

 crease 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 



VOL. XXXV. 38 



