I -in sics, PROGRESS OF, IN 18M. 





tinfoil plate-; in \\ater produced a like c(T-ct, tin- 

 foil from tobacco packages being very sensitive. 

 Tin- lnM plates, however, wen- made bv coating 

 tinfoil with white oxide of tin. Alcohol 

 foiiinl to Iv the l>eM liquid*. A discussion as to 



.ells took place ill the London Physical 



So.-ieiy. .11 Feb. i:{. In answer to a question as 

 to the source of their energy, Prof. Minchiti re- 

 plied that then- is a direct transformation of the 

 light energy without ehi-mical change. 



trnniotii'i' Force. A. Oberbeck and J. 

 Kdler (Wiedemanifs "Annalen," xlii, 2) con- 

 . hide, from experiments on the electromotive 

 force of galvanic elements, that the force can 

 be calculated from the heat equivalent of tho 

 chemical process, taking into consideration the 

 local evolution of heat at the electrodes. Want 

 of constancy they think due to taking up of 

 molecular layers of a dilute solution of the metal 

 of the electrode. G. J. Burch and V. II. Veley 

 (London Royal Society, Nov. 27) have investi- 

 gated the variation of the electromotive force 

 of cells made up of certain metals with platinum 

 and nitric acid. With copper, silver, bismuth, 

 <>r mercury the electromotive force rises to a 

 constant value, which is generally a maximum. 

 This i> duo to decomposition of the acid to form 

 nitrous acid ; for if nitrous acid be added, the 

 maximum is attained at once, and if some sub- 

 stance is added to neutralize the nitrous acid, 

 the rise is ext remely slow. Dr. G. Gore (" Philo- 

 sophical Magaxine,'' July) finds that great 

 changes of voltaic energy take place during the 

 melting of alloys, the most sudden effect being 

 with those that exhibit the most sudden lique- 

 faction. This fact may be used to detect physi- 

 cal and chemical changes in allo\ -. 



Conductivity. E. Brauly (" La Lumiere Elec- 

 trique." May 16) has studied the phenomenon of 

 variation of conductivity in powders. It has 

 long been known that pressure diminishes their 

 resistance. Brauly finds that it is lessened also 

 by a Leyden-jar discharge in the vicinity, by the 

 proximity of a conductor traversed by a con- 

 denser discharge, and by induced currents, or 

 continuous currents of high electromotive force, 

 passed directly through the powdered substance. 

 Some powders for instance, a mixture of sulphur 

 and aluminum require both pressure and elec- 

 tric influence. In further experiments (Paris 

 Academy of Sciences, Xov. 24) he finds that in a 

 circuit composed of a Daniell cell, a high-resist- 

 ance galvanometer, and a thin film of copper 

 7x2 centimetres on ground glass or ebonite, 

 only an insignificant current passes; but if a dis- 

 charge from a Wimshtirst machine or a Ruhm- 

 korff coil takes place in the neighborhood, even 

 at a distance of several metro, t here is a sudden 

 diminution of resistance. X. G. Klassen <('am- 

 bridge Philosophical Society, Jan. 20) finds that 

 the electric resistance of a sulphuric acid solu- 

 tion varies nearly with the viscosity, attaining a 

 maximum at a dilution corresponding to the 

 hydrate M a S0 4 ,H(). but the analogy dimin- 

 ishes with the rise of temperature, probably on 

 account of dissociation of trie hydrate. Shelford 

 Bidwell (London Physical Societv, Dec. 6, 1890) 

 has succeeded in utilixing the well-known sen-i- 

 tiveness of selenium to light in the construction 

 of an automatic electric lamp, which lights itself 

 at twilight or whenever tho room is darkened. 



Pr.-f.NV. I \,non and T. Muth.-r (ibid.. Juno 

 20) have devised several forms of iinn-im: 

 re>i-tance. One consiatfl of strips of thn. 

 platinum, metres by 4 centim. 

 doubled backward on itself, with hilk between 

 the two portions. Twelve of these in 

 a resistance of 2*05 ohms, and would ;. 

 current of 15 amjx}res without a change of more 

 than 0-1 per cent. 



J:'/fctrolysit. Ostwald (" Journal of the 

 Chemical Society," December, 1MM)) has ii. 

 gated the electric properties of semi-pcrmeublc 

 walls. This property of a wall depend- 

 ability to let through the separate ions of an 

 electrolyte. If a solution whose ions can not pass 

 be electrolyzed, the wall will act lik- a metallic 

 electrode. Svante Arrehcniu- i\\ iedemann's 

 "Annalen," xlii, 18) reverses the methods of 

 Van't Iloff by arguing from the electrolytic 

 properties of a dilute solution to those of a ga*. 

 lie investigates the conduction of electricjty by 

 the vapor of heated salts, and finds their be- 

 havior analogous to that of solutions of the same 

 salts. 



M. Chabrv, of the French Societc de Biologie. 

 has succeeded in producing a pressure of 1.W.O 

 atmospheres by electrolytic generation of gas in 

 a closed space. The liquid was a 25-per-cent. 

 soda solution. Both electrodes were of iron; 

 < i;e was the hollow sphere in which the gas was 

 collected, the other was an inner tube. The 

 current had a strength of 1$ amperes. The 

 highest pressure previously produced by this 

 method was 447 atmospheres (Gassiot). 



.A'/* <li !< Evaporation. Prof. William Crookes 

 (London Royal Society, June 11) gives this name 

 to the phenomenon discovered in 1877 by Prof. 

 Arthur W. Wright, of Yale, namely, that a 

 stream of metallic molecules passes from one 

 electrode to another when the electric discharge 

 passes through a vacuum, and that a metallic de- 

 posit can be made on an interposed sheet of glass. 

 This process has been used for silvering mirrors 

 nnd for obtaining thin metal films, but Prof. 

 Crookes is the first to investigate it exhaustively. 

 lie finds that it is similar to ordinary heat evap- 

 oration, the presence of air lessening it as i 1 

 ens common evaporation, but in a greater de- 

 gree. The following table shows evaporation 

 from cadmium electrodes in 30 iniiiir 



In a few hours 850 grains of the metal wen- 

 evaporated. Fro.n silver electrodes in an hour 

 and a half O'Ol grain and O'lO grain were vola- 

 tilized. With the purple gold-aluminum alloy 

 discussed by Prof. Roberts-Austen, the gold 

 evatwmited lir-t. leaving the other metal. 



The comparative electric volatilitiesof metals, 

 calling that of gold 100, are as follow: 



rallailium 10S 



C..I.1 1'NI 



Silver 82-<N 



T^ad 7.V04 



Tin 66-98 



Brass 81 W 



Platinum ............ 44 



CopjMT .............. 4 



Cadmium ............ 



Irldium 

 Irun 



