366 MESSES. V. H. VELET AND J. J. MANLEY ON 



outline the methods and arguments used by PICKERING* in his investigations on 

 sulphuric acid. 



Pure acids and clean vessels are glib phrases, which represent unattainable ideals ; 

 we only trust that we have adopted reasonable precautions of purification, and that 

 even if our determinations are not of absolute exactitude, yet the arguments deducible 

 from them are not seriously affected. 



Lastly, we desire to express our obligations to the Rev. F. JERVIS-SMITH, of 

 Trinity College, Oxford ; Mr. E. H. GRIFFITHS, of Sydney Sussex College, Cambridge, 

 for assistance in the experimental portion ; to Mr. R. T. GUNTHER. for photographs ; 

 to the Chemical Department of the University of Oxford, for loan of apparatus ; 

 to Mrs. V. IT. V.ELEY, for certain illustrations ; and to the Government Grant Com- 

 mittee of the Royal Society for moneys to defray a moiety of the expenses. The 

 work was conducted partly in the Chemical Department of the University Museum, 

 and partly in the laboratory of Magdalen College. 



FORMER INVESTIGATIONS ON ELECTRIC CONDUCTIVITIES. 



KOHLRAUSCH and GROTRiANt determined the conductivity of dilute nitric acid 

 of concentrations varying from 6'32 to 62 - 07 per cent., seven points in all, and at 

 three different temperatures for each concentration, in order to deduce the values of 

 the constants a and /3 in the equation 



These writers adopted their well-known method of alternating currents, but allowed 

 that the acid used was impure, as they wrote : " Die concentrirte Salpetersaure, 

 ursprunglich farblos, hatte nach langerem Stehen eine hellgelbe Farbung angenommen, 

 offenbar durch Bildung eines Spurs von salpetriger Siiure unter dem Einfluss des 

 Lichtes." Their investigations, however, brought out an interesting detail, namely, 

 that the conductivity increases with the percentage concentration up to 30 to 33 per 

 cent., and subsequently decreases ; in the sequel this point will be more fully 

 discussed. 



OSTWALD,! adopting KOHLRAUSCH'S telephone method with slight modifications, 

 made a number of determinations of the molecular conductivity of nitric acid, diluted 

 so as to contain a gram-molecular weight in volumes of water varying from 2 to 

 8,192 litres. 



Finally, BOUTY studied the changes in conductivity caused by the solution in 



* ' Journal of the Chemical Society,' 1890, Trans., 64-184. 

 t ' Ann. Phys. Chem.,' vol. 154, pp. 215-239. 



J 'Journ. Prakt. Chem.,' vol. 30, p. 228, and vol. 31, p. 437; also ' Zeits. Physickal Chem.,' 

 vol. 1, p. 75. 



' Compt. Bend.,' vol. 106, p. 595. 



