324 Scientific Intelligence. 



ture of boiling sulphur in presence of a large excess of air, 

 showed no sign of dissociation ; although according to Troost, it 

 is dissociated when thus treated under a diminished pressure. 

 An experiment with sulphur itself at this temperature, in an at- 

 mosphere of nitrogen, gave a vapor-density corresponding to the 

 formula S 7 ; but this result is apparently accidental. — Zeitschr. 

 physikal. Chem., vi, 5; J. Chem. Soc, lviii, 1365, Dec. 1890. 



G. F. B. 



3. On the Dispersion of Carbon Compounds. — Measurements 

 of the refractive and dispersive powers of the simple and mixed 

 ethers of the methane series by Barbier and Roux show that 

 the dispersive power and the specific dispersive power increase 

 with the molecular mass, but remain practically the same for all 

 isomerides containing the same quantity of carbon. The intro- 

 duction of CH 2 into the molecule raises the specific molecular 

 dispersive power by about 8*2. In methyl-, ethyl- and propyl- 

 allyl ethers the dispersive power and specific dispersive power 

 remain practically constant and do not increase with the molecu- 

 lar mass. If these ethers are compared with others containing 

 the same number of carbon atoms, it is seen that the dispersive 

 power increases as the proportion of hydrogen decreases. With 

 methyl-, ethyl-, propyl-, isobutyl- and amyl-benzyl ethers, the dis- 

 persive power diminishes as the molecular mass increases, but the 

 addition of CH 2 produces a variation in the specific molecular 

 dispersion equal to about 8-2, as in the methane series. In all 

 cases the specific molecular dispersive power of the ethers is 

 equal to the sum of the dispersive powers of the two alcohols 

 from which they are derived, less the dispersive power of the 

 water eliminated. — C. it., cxi, 180; J. Chem. Soc., lviii, 1353, 

 Dec. 1890. G. P. B. 



4. On the Electrical Properties of Semi-permeable Walls. — A 

 semi-permeable material, according to Ostwald, is a material 

 which permits the solvent to pass through it but not the dissolved 

 salt. The permeability of a given material, however, depends 

 not on the nature of the given salt as a whole, but upon the 

 character of each of its ions. Copper ferrocyanide for example 

 is permeable by potassium chloride, because it allows both the 

 potassium and the chlorine ions to pass through it. But it is not 

 permeable by barium chloride because it does not permit the 

 barium to pass, nor by potassium sulphate because it does not 

 allow the passage of the S0 4 ions. If a solution the ions of 

 which cannot pass through a semi-permeable material be electro- 

 lyzed, the electrodes being separated by a semi-permeable wall, 

 the latter will itself act as a metallic electrode. In the author's 

 experiments, a U-tube filled with a solution of potassium ferro- 

 cyanide and having parchment paper tied over its ends, was used 

 to connect two glasses containing solution of copper sulphate ; 

 so that a layer of copper ferrocyanide formed on the paper. 

 After passing a current through the apparatus for a time, metallic 

 copper was found to be deposited on the paper in the glass con- 



