Chemistry and Physics. 67 



a solution may be calculated from the solution pressure of the 

 metal and the osmotic pressure of the solution ; and hence it 

 follows that the electromotive force of a galvanic cell formed by 

 -combination of two different electrodes is easily obtained. Con- 

 versely, Le Blanc in 1891 determined the minimum electromotive 

 force required to produce sensible electrolysis in a given solution. 

 Since theory and practice were somewhat discordant, Le Blanc 

 considered that in some cases water might act as a primary elec- 

 trolyte and suffer direct decomposition by the current. Accord- 

 ing to his measurements 1*68 volts are necessary to do this; while 

 Smale working under Ostwald's direction gives 1*08 volts as the 

 maximum. Investigations made by Glaser in the author's labora- 

 tory show that in the case of sulphuric acid and potassium 

 hydroxide solutions, a primary decomposition of water can be 

 effected with an electromotive force of 1-08 volts, provided the 

 positive platinized electrode on which the oxygen separates be 

 large enough. The value 1*68 volts characterizes further decom- 

 position in these solutions. Nernst suggests that possibly there 

 may be dissociation of the water not only into the ions OH and 

 H, but also into H, H and O, and that the latter ions correspond 

 to the lower electromotive force, while the hydroxyl and hydro- 

 gen ions are set free by the higher one. An interesting table is 

 given showing the voltage necessary to separate certain kations 

 and anions from solutions of normal concentration. These are : 

 Ag— 0-78; Cu —0-34; H 0*0 ; Pb + 0*17; Cd + 0-38; Zn + 0'74 for 

 kations; and I 0*52; Br 094; O 1-08; CI 1*31 ; OH 168; S0 4 

 1*9; HS0 4 2*6 for anions. To calculate the electromotive force, 

 for example, required to electrolyze a normal solution of zinc 

 bromide we have 0*94 + 0'74 = r68 volts; while to decompose 

 hydrogen chloride there is needed 1*31 +0 = 1*31 volts. More- 

 over lrom the above values a conclusion can be reached as to the 

 possibility of separating certain ions electro] ytically. Electro- 

 motive force, however, is only a single factor in these changes ; 

 the other factor, ionic concentration, must also be taken into the 

 account. — Ber. Berl. Ghem. Ges., xxx, 1547-1563, July, 1897. 



G. F. B. 



3. On the Direct production of Iron Carbide. — As a crystal- 

 line carbide of iron Fe 3 C has been shown by several observers to 

 exist in fused or annealed steel, Moissan has investigated the 

 direct action of carbon on iron in the electric furnace. When 

 pure iron is heated with charcoal from sugar in this way, the 

 mass becomes more and more viscous as the temperature rises, 

 resuming its fluidity as it cools. But only about one per cent of 

 carbon in combination was found in the cold metal. If therefore 

 carbon and iron unite at a high temperature, dissociation must 

 result as the mass cools. The same is true of nickel. In prepar- 

 ing diamonds it had been noticed that the interior of the iron 

 contained brilliant crystals resembling iron boride or silicide. 

 The conditions necessary to ensure combination, apparently, are 

 to avoid saturating completely the iron with carbon, and to pre- 



