636 



PHYSICS, PROGRESS OP, IN 1892. 



February) concludes that there seems to be no 

 satisfactory reason for imagining the existence 

 of any sharp boundary between solution and 

 pseudo-solution. In a continuation of his re- 

 search he studied colloidal solution from the 

 state where the dissolved, or rather suspended, 

 particles were large enough to be visible, to that 

 where they were so fine as to diffuse ; and he 

 found complete continuity from suspension 

 through colloidal solution to non-electrolytic 

 crystallizable solution. He concludes that there 

 is a certain degree of molecular attraction 

 throughout, and that it would be but a step 

 farther to electrolytic solution. On the other 

 hand, C. E. Linebarger (" American Journal of 

 Science," March) finds that colloidal solutions of 

 tungstic acid diffuse at a definite rate and have 

 a definite osmotic pressure, and concludes that 

 colloidal solutions are not emulsions, though 

 only a step removed from them. The phenomena 

 are explained by supposing the colloid molecule 

 to be very large. The lowering of the freezing 

 point in a solution of alcohol, according to the 

 experiments of L. de Coffet (Paris Academy of 

 Sciences, Oct. 31), is sensibly proportional to the 

 quantity of alcohol, but the lowering of the 

 temperature of maximum density is not propor- 

 tional. For weak solutions there is no lowering 

 at all, but rather an elevation. 



Capillarity. Lord Rayleigh (" Philosophical 

 Magazine," February) proves mathematically the 

 existence of a capillary force connected with the 

 suddenness of transition from one surface to an- 

 other, which may disappear when such transition 

 is gradual. On the walls of a tube above the 

 point where the liquid seems to end there is yet 

 a thin layer gradually diminishing in thickness 

 and reaching to an immense height. At every 

 point the fluid must be in equilibrium with the 

 vapor at the same level. Later (ibid., May) he 

 establishes the law that the lowering of tension 

 due to thin films is proportional not to their 

 thickness but to its square. In August (ibid.), 

 in treating of the instability of a cylinder of vis- 

 cous liquid under capillary forces, he shows that 

 long threads of such liquid do not tend to divide 

 into drops at a distance comparable to the diam- 

 eter of the thread, but at few and distant places. 

 Albert Colson (Paris Academy of Sciences, Nov. 

 23), by experiments on the flow of liquids in 

 capillary tubes, has proved that ethers and alde- 

 hydes are perfectly mobile, and obey Graham's 

 law that duration of flow is inversely as the 

 square root of the density, but that alcohols and 

 benzines, being imperfectly mobile, give irregu- 

 lar results. His figures for glycerin at different 

 temperatures are as follow : 



Temperature 21 100" 150* 250 265 



Duration of flow.. 8 hrs. 860 sec. 114 sec. 40 sec. S3 sec. 



Mr. Blakesley, in a discussion at the London 

 Physical Society (Nov. 6), said that when water 

 evaporates from a glass a furrow is formed at 

 the original boundary, as if the glass had been 

 torn there by molecular action, snowing the in- 

 creased energy at the surface. Gossart (" Journal 

 of the Chemical Society," February) has utilized 

 the fact that a liquid may be made to roll on it- 

 self in drops, to detect impurities. The rolling 

 is made possible by the formation of a film of 

 vapor, which in pure liquids is absorbed at once. 



These, therefore, never roll, and the life of the 

 drops depends directly on the amount of impu- 

 rity present. By comparison with a standard so- 

 lution, the per cent, of impurity may be found 

 within y-^j. Each impurity behaves as if it alone 

 were present. Lord Rayleigh ("Philosophical 

 Magazine," April) shows that water will spread 

 on a clean surface of mercury as theory requires. 

 To obtain a clean surface, it is sufficient to draw 

 the mercury by a faucet from beneath the free 

 surface of the reservoir. He has also observed 

 that lycopodium dusted on a water surface re- 

 cedes from the edge and leaves a perfectly clear 

 ring. This is not due to grease, but purely to 

 gravity, for when the vessel is filled to overflow- 

 ing, so that the surface is convex at the edge, the 

 lycopodium moves outward. 



Osmotic Pressure. Tamman (" Zeitschrift fur 

 Physikalische Chemie," February) has observed 

 that the osmotic pressure of a salt solution, cal- 

 culated by the formula of Arrehenius, is always 

 smaller than that observed by the usual method, 

 and shows that this is due to the fact that the 

 membrane is not perfectly impermeable to the 

 salt employed. He therefore makes his measure- 

 ments by employing external pressure to balance 

 the osmotic pressure. 



Viscosity. R. Cohen (Wiedemann's "An- 

 nalen," No. 4, 1892) shows that the viscosity of 

 water is diminished by pressure up to. 40, no 

 minimum being observed at a temperature of 

 25 up to a pressure of 900 atmospheres. The 

 change of viscosity increases more slowly than 

 the pressure. The viscosity of water varies 

 greatly with the temperature. In concentrated 

 solutions of common salt and ammonium chlo- 

 ride the viscosity increases with pressure, and its 

 change is nearly proportional to the pressure. 

 The more dilute the solution is, the more does 

 the anomalous behavior of the water influence 

 it. The viscosity of oil of turpentine alters with 

 pressure 20 times as rapidly as that of a satu- 

 rated salt solution. 



Density. Paul Galopin (Paris Academy of 

 Sciences, June 2) finds that increase of pressure 

 lowers the temperature of maximum density of 

 water for that particular pressure, and that 

 under high pressures it corresponds nearly to 

 the freezing point. 



Compressibility. E. H. Amagat (Paris Acad- 

 emy of Sciences, Oct. 31) has found that in ether, 

 alcohol, carbon disulphide, acetone, etc.. the co- 

 efficient of compressibility decreases regularly as 

 the pressure increases. At 3.000 atmospheres 

 that of water is reduced by one half, and that of 

 ether by two thirds. This diminution is greater 

 the higher the temperature. 



Extensibility. A. M. Worthington (London 

 Royal Society, Feb. 4) has observed the volume 

 extensibility of ethyl alcohol by sealing it in a 

 strong glass vessel, which it nearly fills, the re- 

 maining space containing only its own vapor. 

 On being heated it expands and fills the vessel, 

 but on cooling it sticks and does not shrink at 

 once, and thus is for a time under tension. He 

 finds that stress and strain are proportional up 

 to the highest tension used that of 17 atmos- 

 pheres and that the apparent compressibility is 

 the same as the apparent extensibility. 



Bubbles in Water. F. T. Trouton (British As- 

 sociation) finds that the speed of ascent of air 



