The outlines of physics: an elementary text-book . t wet, thefilm is stronger, and it depresses the liquid below the gen-eral level, as already described. 134 THE OUTLINES OF PHYSICS Fig. 1H. 118. Angle of Contact. — The curvatureof the liquid film in the neighborhood ofsolids depends, as has already been shown(Art. 115), upon the relative strength ofthe molecular forces within the liquid andbetween liquid and solid. This relationdetermines the angle of contact, by whichthe capillary behavior of liquids in variouscontaining vessels may be defined. Thisis the angle «, Fig. 114, which the filmma
The outlines of physics: an elementary text-book . t wet, thefilm is stronger, and it depresses the liquid below the gen-eral level, as already described. 134 THE OUTLINES OF PHYSICS Fig. 1H. 118. Angle of Contact. — The curvatureof the liquid film in the neighborhood ofsolids depends, as has already been shown(Art. 115), upon the relative strength ofthe molecular forces within the liquid andbetween liquid and solid. This relationdetermines the angle of contact, by whichthe capillary behavior of liquids in variouscontaining vessels may be defined. Thisis the angle «, Fig. 114, which the filmmakes with the solid wall at the point ofcontact. The angle may be greater, equalto, or less than 90°. In the first case there will he depression,in the last elevation, in capillary tubes. 119. Experiment 30. —Van der Mensbnigghes Experiment show-ing that a Liquid Film is always under Tension. Apparatus : (1) A -wire ring about 10 cm. in diameter, -within which hangs aloop of thread as shown in Fig. 115. (2) A dish containing a soap Fig. 115. Procedure : (a) Dip the ring into the solution, whence it emerges carrying aplane soap film bounded by the ring and completely filling it, Theloop of thread may be seen floating in the liquid layer within which / SURFACE FILM OF LIQUIDS 135 that outside of the it moves freely, excepting as it is constrained by the strand whichconnects it with the ring. (V) The film consists of two distinct regions:loop of thread and that within the loop. Puncture the latter region with any con-venient tool, such as a pin or needle or a bitof wire. The result, which follows instantly,is most beautiful and striking. The thread,hitherto lax, is drawn intocircular form by the tensileforces of the outer region of the film whichare no longer balanced by those of the regionwithin the loop. It is now held tensely toits position of equilibrium within the film(Fig. 116), and its laxity and freedom of motion have disappeared. If the ring used in this e
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
