PHY>!( s, PI;<MJKKSS <F, IN 



727 



body, however clenn, contaminates a water sur- 



Kelativc contamination may U- im 



In deerea-mg I III- contaminated \\atlT Mirfaci- 



ti'll it lii-comcs anomalous, and then taking the 

 rat in i. f it.- iiri'a to tin- original iin-a. 

 With equal relatire contamination liy tin- same 



sub-taner, there is no current from mie surface 

 tn aimtlii-r, hut there is always a cunvnt from 

 tin- greater tn tin- less contamination. With dif- 

 fi-n-iit substaiico llirrr is a current, even if the 

 relative contaminations arc equal. For instance, 

 a current Hows from a glass-contaminated to a 

 metal-contaminated surface. She concludes that 



water dissolves even glass aiul metals at its sur- 

 face, and that the surface layer can take up more 

 than the internal liquid. (See So/iitin/i. ahove.) 

 (J. Van der Mensbrugghe (Brussels Royal Acad- 

 emy of Sciences, April 4) concludes that the com- 

 mon surface of two liquids that act on one an- 

 other is subject to a force whose direction is 

 away from the center of curvature. A case in 

 point is the slow diminution of tension between 

 oil and \vater, probably due to chemical action. 



OryttaXKiafam, Prof. Tito Martini, of Ven- 

 ice (" Hivista Scientifico-Industriale," June), has 

 investigated the crystallization of thin liquid 

 films. With a solution of sodium sulphate near 

 its saturation point films can be formed as with 

 a soap solution. If one of these be evapo- 

 rated rapidly, a lattice-work of minute crystals 

 will remain. These finally effloresce and fall 

 apart. Crystal lilms 36 millimetres in diame- 

 ter were thus formed, and the experiment suc- 

 ceeded also with ammonium chloride and sodium 

 hyposulphite. Lehmann, who has already noted 

 that the optical behavior of certain liquids sug- 

 gests a crystalline structure, now ("Journal of the 

 Chemical Society," March) raises the question 

 whether isotropici liquids arc non-crystalline or 

 crystalline and isometric. He concludes that 

 they are non-crystalline, in view of the free mis- 

 ciliility of liquids. The same experimenter shows 

 that crystals melted bet ween glass plates retain on 

 cooling and recrystallization the former direct ion 

 of their optic axes. This may be due to a non- 

 melted layer that adheres to the gla-s. 



Exploit 'ri' Wai-?*. Berthelot (Berlin Chem- 

 ical "Berichte," April) shows that the speed of 

 these is not so regular in liquids as in . 

 Methyl nitrate in a steel tube explodes at the rate 

 of about 2,100 metres per second. 



Evaporation. P. de Heen (Brussels Academy 

 of Sciences, .January 20) concludes that the ve- 

 locity of evaporation at the boiling point is pro- 

 portional to the square root of the velocity of 

 the superficial gas current, and that for a given 

 velocity the quantity vaporized is as the vapor 

 tension. 



Gases. Compressibility. Ulyssc Lala (Paris 

 Academy of Sciences, Dec. 1, 1890) announces 

 that, between the pressures of 100 and 1,613 

 centimetres of mercury, the compressibility of 

 a mixture of air and carbon dioxide (when the 

 per cent, of dioxide does not exceed 22) is be- 

 tween the compressibilities of the two gases. It 

 increases in a mixture richer in dioxide. Later 

 (Feb. 23) he announces that the compressibility 

 of a mixture of air and from 16 to 31 per cent. 

 of hydrogen lies (for pressures near 100 centi- 

 metres of mercury) between these of the two 

 gases, but with larger proportions of hydrogen 



Mtropi'n 

 Ilydtogcn 



and higher procures the mixture becomes lew 

 eompn-.-ihlc than h \dmgen itx-lf. K. 11. 

 gat (il)id. l)n . v . ] y -!Hii hus Mudicd ti. 

 MOII and expansion of liquids und pi-. 

 new method. He finds that between < 

 ('. and l>ctweeii 100 and 1,000 attm, i 

 the coeflicieiit of expansion of Imlr- - 

 constant pressure diminishes wilh'inci,. 

 pressure. With oxygen, nitiopn. and air the 

 coefficient is a maximum at the beginning. At 



constant volume ^ is always greater from 0* 



to 100 than from 100 to 200. The following 

 results are for tempciaturo lctwc< n and 100" 

 and a pressure ol ;iio atmosphi : 



Oxyjfcn ............ .. Sftis i 



Air .................. 8-tt-S | 



Combustion under Pretwure. H. W. Wood 



(" American Journal of Science," June) finds 

 that a burning jet of coal-gas is extinguished at 

 a pressure of X!:' cenlimetics of mercury; that 

 is, when the velocity of the i>suing gas exceeds 

 the speed of combination for a mixture of gas 

 and air. 



Pneumatic Bridge. This device, the invent ion 

 of W. II. Shaw (London Physical Society, .May !)). 

 ima.Mircs the pneumatic resistance of various 

 orifices and channels as Wheatstonc's bridge 

 measures electrical resistance. Two arms of the. 

 bridge consist of circular holes in thin mica 

 plates; the third arm is an aperture with a slid- 

 ing shutter regulated by a screw; and the fourth 

 is the aperture to be measured. The battery is 

 replaced by a Bunsen burner and the galva- 

 nometer by a glass tube with a sensitive vane. By 

 means of this apparatus it has been proved that 

 beveling off one side of a hole in a thin plate in- 

 creases its pneumatic conductivity, especially 

 when the beveling is on the side of egress. F..'r 

 square-ended tubes the conductivity first in- 

 creases with length and then diminishes, but a 

 beveled mouthpiece causes this effect to disaj)- 

 pear. 



Sound. Rotation of a Vibrating Body. If a 

 cylindrical vibrating rod be rotated on its axis, 

 the plane of vibration does not turn with it but 

 remains fixed in space. But in the case of a 

 tuning-fork the beats heard indicate that the 

 planes turn with the fork. (i. II. Bryan (Cam- 

 bridge Philosophical Society. NOT. 4, 181)0) 

 shows that when a bell or other body symmetri- 

 cal about an axis thus vibrates, tlie'eff'ect is in- 

 termediate. The nodes rotate, but with a smaller 

 velocity than that of the lx>dy. 



IntfHKi'/i/ of X<.nn<l.--~('. \\. Wcad ("Ameri- 

 can Journal of Science," March) notes that not 

 the amount of energy in a vibrating Imdy but 

 the rate at which it is given up to the air deter- 

 mines the intensity. Text-books, he ;. 

 therefore err in stating that loiidness varies with 

 the square of th amplitude. In the same maga- 

 zine for July Mr. Wead shows that no conclusions 

 can be drawn from the loiidness of the sound of 

 organ pipes, a- to the relative amplitude of vibra- 

 tion within. The >oft Dulcinea stop takes more 

 than half as much wind as the loud trumpet. This 

 shows the higher eflicieiiey of reed Mops. In dif- 

 ferent pipes belonging to the same st< p the o n- 

 sumption of wind docs not at all ngrt-* 1 with 

 theory. For example, any note should take only 



