108 C. E. Linebarger — Apparatus for the Hapid 



Art. Xiy. — A71 Apparatus for the Rapid Deter mynation 

 of the Surface Tensions of Liquids ; by C. E. Linebar- 

 ger. 



I. Introductory. 



The essential difference between the gaseous state on the 

 one hand and the liquid and solid states on the other hand is 

 that in liquids there exists a pressure directed towards their 

 interior, while in gases such a pressure seems to be wanting, 

 particularly when the gases are far removed from their point 

 of condensation. This internal pressure is attributed to the 

 mutual attractions of the molecules of bodies, its amount being 

 in inverse proportion to the mean molecular distance. Thus, 

 if the molecules of a portion of matter be comparatively far 

 apart, their reciprocal influences are negligibly small, but, as 

 they come closer and closer together, their attractions become 

 appreciable in the variations shown by gases under certain con- 

 ditions to the Laws of Boyle and Charles, and eventually, the 

 attractions become so great that the gas condenses into a liquid 

 with its horizontal surface, slight compressibility, etc. 



In liquids, the internal pressure is undoubtedly exerted 

 equally in all directions ; in crystalline solids, however, its 

 amount may vary with the direction, unless they be isotropic ; 

 in colloids, finally, which may be regarded as exceedingly vis- 

 cous liquids, the internal pressure is the same in all directions. 



Although the internal pressure has long been recognized to 

 be of prime importance in the investigation of the nature of 

 liquids, but little that is more than approximately quantitative 

 is known concerning its amount. This is due to the circum- 

 stance that as yet no experimental methods have been devised 

 which can give direct determinations of it, since it has been 

 found impossible to connect the interior of a liquid with a 

 manometer without the intervention of its surface. Our quan- 

 titative knowledge of the internal pressure is obtained indi- 

 rectly by assuming theoretical relationships between its amount 

 and some of the properties of liquids (latent heat of vaporiza- 

 tion, volume, changes, etc.,) or solutions, which are susceptible 

 of direct measurement. All of these indirect methods agree 

 in assigning to the internal pressure an enormous value, 

 hundreds of atmospheres, at least, under ordinary conditions. 



The phenomena displayed in the surface of liquids, the so- 

 called capillary phenomena, are, perhaps, more intimately 

 related to the internal pressure than any other property of 

 liquids. The importance of these capillary phenomena in 

 Nature's happenings does not seem to have always been fully 

 realized. Nearly all interactions of bodies that can be thought 



