Chemistry and Physics. 157 



from the osmotic pressure and dissociation hypothesis. Nernst 

 and Patjli have now determined experimentally the electromo- 

 tive forces produced in liquid cells made by the combination of 

 decinormal and centinormal solutions of potassium chloride and 

 hydrogen chloride and have compared their results with those 

 obtained from theory in 1890. The agreement between theory 

 and observation is quite satisfactory. Consequently it follows 

 that, since solutions of zinc sulphate and of copper sulphate hav- 

 ing equal molecular concentrations, are both very nearly disso- 

 ciated into ions, there should be no considerable electromotive 

 force at their surface of contact. Now on investigating the com- 

 bination 



Hg | HgS0 4 | l/10n CuS0 4 | l/10n ZnS0 4 | HgS0 4 | Hg 



the aiUhors have found that in fact the electromotive force devel- 

 oped is only -00024 volt. Hence the contact of the two liquids in 

 a Daniell cell is not the seat of an appreciable electromotive force. 

 — Ann. Phys. Chem., II, xlv, 353; J. Chem. Soc, xlii, 671, June, 

 1892. G. F. B. 



4. On the Separation of Precipitates at the Surface bounding 

 Electrolytes. — It was long ago observed by Faraday that if a 

 saturated solution of magnesium sulphate be placed in the bend 

 of a U-tube and a layer of water be placed in each limb of the 

 tube resting upon the sulphate, so that the two liquids do not 

 mix, then on passing a current through the whole, a precipitation 

 of magnesium hydroxide takes place at the surface which sepa- 

 rates the sulphate from the water containing the negative elec- 

 trode. In 1887, Herrmann repeated these experiments with zinc 

 sulphate. Kttmmell has now investigated the matter more thor- 

 oughly, using in place of aqueous solutions of the metallic sul- 

 phates, solutions prepared with sufficient gelatin so that they 

 solidify on cooling. The presence of the gelatin does not inter- 

 fere with the phenomenon in question while at the same time it 

 prevents the admixture of the solution and the water, which it is 

 not easy to prevent otherwise. Experimenting in this way, he 

 found that of the many sulphates examined, the precipitation 

 occurred only with those of magnesium, zinc, cadmium and alumi- 

 num. The separation of the hydroxide always takes place first, 

 at the negative electrode itself; the appearance of the precipitate 

 at the boundary of the two liquids taking place later. By modi- 

 fying suitably the method of experimenting it was ascertained 

 that the phenomenon is due to a transfer of the solid particles 

 from the negative electrode through the feebly conducting water 

 by the electric current. — Ann. Phys. Chem., II, xlvi, 105; J. 

 Chem. Soc, xlii, 1038, Sept., 1892. G. f. e. 



5. On Chemical Phenomena at low Temperatures. — Pictet 

 has experimented on the chemical and physical phenomena observ- 

 able at very low temperatures. He finds that by means of 

 powerful compressors and aspirators, a mixture of sulphur dioxide 

 and carbon dioxide will give a temperature of — 1 10°, nitrogen 



