physics. 577 



the liquid and the gaseous condition under pressures Up to 120 atmos- 

 pheres, the viscosity being measured by the velocity of flow through 

 capillary tubes. The gas above the critical temperature showed no 

 minimum of viscosity at the maximum of compressibility, but, on the 

 contrary, the viscosity increased with the density. When the density, 

 however, reached 500 times its normal value, the coefficient of friction 

 exceeded its normal value only 9 per cent. With a coustant density 

 the influence of temperature is feebde, though the viscosity appears to 

 increase slowly with the temperature. The liquid has the smallest vis- 

 cosity hitherto observed, its coefficient at 15° being 14.G times less than 

 that of water, and increasing with the density. For densities near 0.8, 

 the viscosity has a minimum value for the temperature of 20° to 32°.0. 

 (J. Phys., March, 1883, II, n, 142.) 



Stables and Wilson have tested experimentally the supposition of 

 Plateau that the surface viscosity in some liquids is greater than the 

 interior viscoscity. They used for the purpose a solution of saponin, 

 in which this property is marked, determining the viscosity by the tor- 

 sional oscillation of a nickel-plated brass disk. The results obtained 

 show that whereas the resistance offered to an oscillating disk 2 mm thick 

 in the surface of water is only about half what it is in the interior, at 

 the surface of a 2 per cent, saponin solution it is at least GOO times 

 greater than in the interior. The ratio of resistances in the case of the 

 saponin solution and water is at the surface, 1261.; at mm .l below the 

 surface, 33; while in the interior it is 1.2. (Phil Mag., June, 1883, V, 

 xv, 406.) 



Wiedemann has examined the question of the condensation of liquids 

 upon solid surfaces, and comes to the conclusion that it is an entirely 

 inappreciable quantity. (Wied. Ann., xvn, 988; J. Phys., II, ir, 232; 

 Phil. Mag. June, 1S83, V, xv, 440.) 



Solution is ordinarily explained by supposing that the salt combines 

 first with a portion of water to form a hydrate more or less stable, and 

 then that this hydrate diffuses through the mass forming a homogeneous 

 mixture. Nicol has suggested the hypothesis that " the solution of a 

 salt in water is a consequence of the attraction of the molecules of water 

 for a molecule of salt exceeding the attraction of the molecules of salt 

 for one auother." As the number of dissolved salt molecules increases, 

 the attraction of the dissimilar molecules is more and more balanced 

 by the attraction of the similar molecules ; and when these two forces 

 are in equilibrium saturation takes place. The author gives experimental 

 proof of the correctness of this hypothesis. (Phil Mag., February, 1883, 

 V, xv, 91.J 



Gernez has measured the duration of solidification in the case of sur- 

 fused bodies. Using phosphorus, for example, in a glass tube not exceed- 

 ing 2 um, .7 in diameter, bent in a U form, the column being or 7 deci- 

 meters long, the whole was placed in a water bath at a temperature 

 above the fusing point. It was then transferred to a water bath main- 

 H. Mis. 09 37 



