570 



PHYSICS, PROGRESS OF, IN 1900. 



where p p' is the diminution in vapor pressure 

 produced by the addition of n molecules of one 

 liquid to X molecules of the other. Ryland 

 (American Chemical Journal, November, 1899) 

 has examined 80 binary mixtures of liquids mu- 

 tually soluble in all proportions and two mix- 

 tures* of liquids whose mutual solubilities are 

 limited. Forty-five of the former give distillates 

 which boil at" a constant temperature., the ratio 

 of the components then being nearly that of the 

 products of the vapor densities and vapor pres- 

 sures of the pure liquids at that temperature. 

 Both of the latter mixtures form distillates with 

 the like property so long as there are two layers 

 of liquids in the distilling flask; these distillates 

 are, however, not true chemical compounds. 



Freezing. Wildermann (Zeitschrift fiir physi- 

 kalische Chemie, Dec. 1, 1899), in experiments on 

 the freezing points of dilute solutions, has ob- 

 tained the following results, among others: 

 When the freezing point is depressed by about 

 0.02 needles or flakes of ice separate through- 

 out the solution, but if the depression is only 

 a few thousandths the ice separates in bands or 

 in a continuous cap on the bulb of the thermome- 

 ter. The freezing point of water, freed from am- 

 monia and carbon dioxide by a current of pure 

 air, varies to a noticeable extent owing to the 

 presence in it of a variable amount of dissolved 

 oxygen and other nonelectrolytic matter. He 

 shows how to calculate the difference between the 

 observed (or apparent) freezing point and the real 

 freezing point. The error varies, according to 

 methods, from 0.00002 C. to 0.004 C. 



Temperature of Flames. Mache (Vienna Acad- 

 emy Sitzungsberichte, 108, 1899) has investigated 

 the temperature gradient in a homogeneous mix- 

 ture of burning gases, such as a detonating mix- 

 ture of oxygen and hydrogen. An explosion trav- 

 els with definite velocity along a tube so filled, 

 the gases on one side of the burning surface 

 having the temperature of combustion, on the 

 other that of ignition. The transition is abrupt. 

 The author shows that the temperature decreases 

 rapidly away from the burning surface, being 600 

 at 12 centimetres distance, 200 at 65 centimetres, 

 and 50 at 22 centimetres. 



Light. Theory. Sagnac (Comptes Rendus, 

 Nov. 13, 1899) considers the luminous vibrations 

 in the interior of a body as being propagated by 

 the intervention of a medium identical with the 

 ether of a vacuum, and differing from it neither in 

 density nor in elasticity. The phenomena usually 

 referred to mechanical reactions between the ether 

 and matter are explained by taking account of the 

 discontinuity of matter. Carvallo (ibid.. Jan. 8) 

 doubts the truth of the received theory that 

 white light is due to a damped vibration. If 

 this were the case, he asserts, the grating spec- 

 trum would give white light over its whole area. 

 The accepted theory neglects radiation which, 

 although insensible to the eye in isolated regions, 

 become of notable amount in the case under con- 

 sideration. Gouy (ibid., Jan. 29) criticises these 

 contentions. He acknowledges that the resolution 

 of white light into simple vibrations is purely 

 fictitious, but maintains that it enables us to cal- 

 culate the total energy spent between two given 

 epochs. Damped oscillations form a workable hy- 

 pothesis, although not the only one. 



Standards. From the results of his work on 

 standards of light, Petavel (London Royal Society, 

 05, p. 469) states that the probable variation in the 

 light emitted by molten platinum under standard 

 conditions is not above 1 per cent., and the ac- 

 curacy of this standard is capable of being in- 

 creased. 



Brightness. Lummer and Kurlbaum (German 

 Physical Society, 2, 8, 1900) find that the ratio 

 of the brightnesses of two hollow platinum vessels 

 at different temperatures is equal to the ratio of 

 those temperatures, taken on the absolute scale, 

 raised to a power that grows less as the tempera- 

 ture increases. 



Reflection. Hagen and Rubens (Annalen der 

 Physik, February) have determined the reflective 

 powers of various metals and of glass mirrors for. 

 the various rays of the visible spectrum by a 

 photometric method. As a general rule, the re- 

 flective power of metals increases with the wave 

 length of the light. Thus the reflective power of 

 gold for rays of wave length 700 is the same as 

 that of silver. 



Double Refraction. Hill (Philosophical Maga- 

 zine, December, 1899) has studied the double re- 

 fraction introduced in solutions of colloids, such 

 as gelatin and gum arable, by stirring, and con- 

 cludes that such solutions are not true solutions in 

 the proper sense of the term, since their behavior is 

 much more like that of an elastic solid, as they are 

 able to sustain strains if not distorted too much. 

 He believes that their structure is similar to that 

 of jellies. 



Interference. Lummer (Berlin Academy, May 

 3) has studied the phenomena observed when one 

 looks at a bright surface through two right-angled 

 prisms placed Avith their hypothenuses together, 

 but separated by a thin film of air, and with the 

 eye focused for parallel rays. A system of inter 

 ference fringes is seen parallel to the line bounding 

 the area of total reflection, and the author has 

 discovered that in reflected light two systems of 

 fringes are obtained, one complementary to tin- 

 other. 



Polarization. Forchheimer (Zeitschrift fur 

 physikalische Chemie, July 3) has proved experi- 

 mentally the substantial truth of Perkins's view 

 that the behavior of salts with relation to electro- 

 magnetic rotation of the plane of polarization is 

 analogous to that of the corresponding acids. So- 

 lutions of the sulphates of ammonium, sodium, and 

 magnesium resemble sulphuric acid in having tlic 

 molecular rotation independent of the concentra- 

 tion, and the same is true of hydrochloric acid and 

 various haloid salts: but with both the sulphate 

 and the chloride of lithium the rotation increases 

 with the dilution, a property that seems to be 

 peculiar to lithium salts. (See also Fliiorrwiirr. 

 just below.) 



Dispersion. Schmauss (Annalen der Physik. 

 June) finds that the general form of the la\v of 

 optical dispersion can also be applied to the dis- 

 persion observed in the Faraday effect, so that 

 the magnetic-rotatory dispersion shows discon- 

 tinuities near the absorption bands of certain 

 substances, just as the optical dispersion dot-. 



Phosphorescence. C. C. Trowbridge (Science. 

 Aug. 25, 1899) finds that the reduction of the tein : 

 perature of a phosphorescing substance is ac- 

 companied by a corresponding decrease in 1 1n- 

 phosphorescent discharge; that very low tem- 

 peratures cause phosphorescence to linger lonr 

 enough to be readily observed in substances not 

 visibly phosphorescent at ordinary temperature-: 

 and that the production of phosphor<--ccnce i- 

 less when excitation occurs at low temperature-. 



/'liiorcxrciicc. Hewitt (Chemical Society IV" 

 ceedings, Jan. 24) finds that the molecules of 

 fluorescent substances are probably those capable 

 of vibrating in two different periods. Flume- 

 cent coloring matters exhibit tautomerism alnio-t 

 without exception. Schincaglia (Nuovo ( 'i 

 niciito. September. 1899) finds that in isotropic 

 substances the light of fluorescence is never po- 





