757 General and Physical Chemistry. Refractive Powers of Isocyanides and Nitriles. By T. COSTA (Gazzetta, 22, i, 104-109).-A comparison of the refractive powers of the isomeric nitriles and isocyanides might be expected to show whether in the latter class of substances the carbon atom in the CN group is bi- or quadri-valent. The author has examined ethyl isocyanide, propionitrile, and benzonitrile; his results are contained in the following table : Molecular The molecular refraction is calculated by means of the formula M(na2 1) The molecular refraction of ethyl isocyanide will be seen d(na+2) to be somewhat higher than that of its isomeride, propionitrile. The carbon atom in the CN group must therefore be supposed to be saturated, and the isocyanide should hence have either the constitution CEN X or X-N:C:CNX. The author has endeavoured to determine the molecular weight of ethyl isocyanide by the cryoscopic method, using benzene as the solvent. On cooling, however, the isocyanide separates, forming an emulsion, and renders the experiment futile. W. J. P. Absorbent Power of Coloured Salts and Electrolytic Dissociation. By G. MAGNANINI (Gazzelta, 22, i, 131-140).-The author criticises unfavourably the deductions drawn by Knoblauch (Wied. Ann., 43, 738) from observations made on the absorption spectra of solutions of coloured salts. Knoblauch concluded that on varying the degree of concentration of the coloured salt solution no change in the absorption spectrum occurred; no photometric measurements were made, however, and the spectra were simply compared by the eye. As, however the most concentrated solutions used by Knoblauch contained the salt in a considerably dissociated condition, were inspection of the absorption spectra could not be expected to afford any criterion of the progress of dissociation as the solution became more dilute. Knoblauch's conclusion, that his experiments are in disaccord with the electrolytic dissociation hypothesis, is therefore unfounded. The author has measured the extinctions for solutions of various coloured salts, reducing the electrolytic dissociation of the dissolved salt by adding to the solution a colourless salt or free acid having one ion in common with the coloured salt. Thus, to solutions of copper sulphate were added considerable proportions of sodium sulphate and sulphuric acid. The coefficients of extinction in this 3 f |