PHYSICS, PROGRESS OF, IN 1898. 



617 



Liquids. tiolulion. H. I". Pickering <" Philo- 

 sophical Maga/ine." 1'Yliruary) finds that the 

 product of tin- molecular weight oi u liquid by 

 the -q nan- of the rate of diffusii m is not constant, 

 \\hich shows that osmotic pressure in a solution 

 is not duo simply to gaseous impact of di>solvc<l 

 molecules, or else that perfection is not attain- 

 able in diffusion experiments. < '. Dieterici 

 (Wiedemann's " Annalen," October) has meas- 

 ured the vapor pressures of aqueous solutions by 

 the movements of an aneroid box, the concentra- 

 tion varying from extreme dilution upward. 

 The curves expressing his results are similar for 

 all solutions, beginning at approximately the 

 same angle, then falling steeply, and finally 

 tending to become parallel to the axis of abcis- 

 sas. Hamburg ("Zeitschrift fur physikalische 

 Chemie," xii, 4) finds that the effect of electro- 

 lytic dissociation on the magnetic rotatory 

 power of a solution is too small to be detected. 



Osmosis. Tain man n (" Journal of the Chem- 

 ical Society," December, 1892), with a view of test- 

 ing the theory that precipitated membranes act 

 as sieves, letting through water, but not the 

 molecules of a dissolved substance, has experi- 

 mented with 3 membranes, respectively of tan- 

 nate of gelatin, zinc ferrocyanide, and copper 

 ferrocyanide, and solutions of 17 acids and salts. 

 He finds that the permeability is the same for all 

 the membranes, and thinks that his results indi- 

 cate the passage of the ions of the acids sepa- 

 rately. The behavior of the salts, however, was 

 anomalous. 



Crystallization. E. H. Amagat(Paris Academy 

 of Sciences, Oct. 16), after melting ice by com- 

 pression at a temperature below zero centigrade, 

 caused the water to solidify in crystals by gradu- 

 ally lessening the pressure. This he calls crys- 

 tallization by decompression. 



Expansion and Compression. E. H. Amagat 

 (ibid.. April 17) finds that with water kept at 

 constant volume the pressure increases rapidly 

 with the temperature. Thus, for unit volume, 

 the coefficient increases fourfold between 10 and 

 100, and the variation is probably more rapid 

 between and 10. The same (ibid., Oct. 31) 

 has investigated the compressibility of ether, al- 

 cohol, carbon disulphide, acetone, ethyl halides, 

 and phosphorus chloride, and finds that the co- 

 efficient of compression always decreases regu- 

 larly as the pressure increases. A t 3,000 atmos- 

 pheres that of water was reduced by nearly one 

 half its ordinary value, and that of ether by two 

 thirds. This diminution is greater the higher 

 the temperature. 



Density. A. Ilanal (Vienna " Berichte," 

 Quoted in "Nature," March 1C) measures liquid 

 density by the following simple method : Two 

 glass tubes are joined by rubber tubing 30 by 1 

 centimetre. One. which has two marks 80 

 centimetres apart, is immersed up to the lower 

 mark in the liquid to be measured, and the other 

 tube is immersed totally in water. On pulling 

 it out, the liquid in both tubes rises till that in 

 the first tube reaches the higher mark. The 

 height of fche water column, on a suitable scale, 

 then measures the density. 



Capillarity. Ramsay and Shields find a close 

 analogy between the equation pv = RT, that 

 holds good for gases, and a similar equation 

 71 = KT, for the surface of a liquid, y being the 



surface tension, the surface area, K a constant, 

 and r the temperature measured downward from 

 a point jilioul (i below the critical point. This 

 relation was found experimentally to hold good 

 for several liquids. T. Proctor Hall, of Clark 

 I'nivcrsity, Worcester, Mass. ("Philosophical 

 Magazine," November), has exhaustively studied 

 met hods of measuring surface tension. He em- 

 ploys three. (1) The weight of a thin horizontal 

 bar having its extremities bent at right angles so 

 as to touch the liquid was taken when a film ex- 

 tended between the bent ends, and also without 

 such film. (2) With liquid- where the film 

 breaks before it is high enough (5 to 10 mm.) to 

 give good results, a set of thin parallel vertical 

 plates in a holder were weighed similarly. (3) 

 With the bar used in the first method, the maxi- 

 mum of weight was taken just before the forma- 

 tion of a true film. This last method was found 

 capable of almost incredible delicacy. Water 

 showed great variations of tension, the averages 

 running from 71 '91 with glass to 73-29 with 

 zinc a smaller result than that obtained by 

 Rayleigh from ripples. De Vries (Royal Acad- 

 emy of Sciences, Amsterdam, Feb. 25) has meas- 

 ured the variation of ascension of ether in capil- 

 lary tubes from 102 C. to 193"*C. The surface 

 work, plotted as a function of the temperature, 

 gives a curve with its convex side toward the 

 axis of temperature and ending tangent to it. 

 C. Maltezos (Paris Academy of Science, Nov. 14) 

 finds that when a liquid spreads over the free 

 surface of a denser liquid, microglobuJes are 

 formed by inverting the liquids. If, on the con- 

 trary, a liquid rests in drops on a denser, in the 

 inverted position the denser will spread over the 

 less dense. 



Viscosity. Barus (" A merican Journal of Sci- 

 ence," February) has found the influence of tem- 

 perature, volume, and pressure on marine glue, 

 and constructed curves showing his results. 

 Among them are the striking preponderant in- 

 fluence of temperature on viscosity. He finds 

 that in proportion as the viscosity increases 

 with fall of temperature, its isothermal rate of 

 increase with pressure also increases. 



Hydrodynamics. P. Rudski (' Philosophical 

 Magazine," May) finds that there are two crit- 

 ical velocities for water in a straight pipe a 

 greater, making quiet motion impossible, and a 

 smaller, making tumultuous motion impossible. 

 When the liquid enters, the motion is tumultu- 

 ous, but with a small velocity viscosity acts and 

 the eddies die out. With increased velocity, 

 however, the eddies break and reform, (i. 11. 

 Bryan (ibid., April), in investigating the motion 

 of a perforated solid in a liquid, finds that no 

 forces act to maintain a screw motion whose axis 

 is coincident with the central axis of the im- 

 pulse. 



Gases. Resistance to Motion. Cailletet and 

 Colardeau (Paris Academy of Science, July 17), 

 using a receiver with a paddle wheel actuated 

 by a weight, find that resistance offered to the 

 motion of a plane is proportional to the surface, 

 the square of the velocity, and the pressure and 

 density of the gas. Two planes separated by a 

 distance equal to the breadth of one met with 

 only I'l time the resistance of one. Two planes 

 0-15 metre broad, even when one metre apart, did 

 not meet twice the resistance of a single one. 



