The Electric Conductivity of Nitric Acid, 223 



consequence. The intensity had diminished, however, by nearly 

 25 per cent. 



Similarly the magnet which had been given a negligible coefficient 

 by cntting the length of the wire to 8 cm., as cited above (p. 219), 

 after being boiled at intervals for fonr hours, was found five months 

 later to have changed so little that its coefficient might still be con- 

 sidered negligible. 



Further experiments, however, upon this question and some others 

 arising out of this investigation are now in progress. 



" The Electric Conductivity of Nitric Acid." By V. H. Veley, 

 M.A., F.R.S., and J. J. MANLEY, Daubeny Curator of the 

 Magdalen College Laboratory, Oxford. Eeceived Novem- 

 ber 1,— Read December 9, 1897. 



(Abstract.) 



In this paper an account is given of determinations of the electric 

 conductivity of nitric acid of percentage concentrations varying 

 from 1*3 to 99*97, purified, so far as possible, from reduction 

 products of the acid, as also from sulphuric and the halogen acids, 

 with which it is likely to be contaminated from its process of manu- 

 facture. In the preliminary experiments it was observed that the 

 results might be vitiated by (i) a trace of nitrous acid either directly 

 added or produced by decomposition due to exposure to sunlight, and 

 (ii) imperfect insulation of the electrolytic cell caused by metallic 

 clamps, a point which seems to have been neglected by previous 

 observers. 



The methods adopted for the purification of the water and nitric 

 acid, as also for the detection and estimation of the impurities, are 

 described in full. The greatest quantity of nitrous acid, sulphuric 

 acid, and the halogen acids found in any sample used were 0*75, 4"3, 

 and 3'8 parts per million respectively. 



The thermometers, resistance coils, and other instruments used 

 were compared with certain standards and corrected accordingly; 

 the burettes and electrolytic cells were calibrated by one or more 

 methods, and the mean of the values accepted. 



The method adopted for the determinations was in outline that 

 originally described by Kohlrausch, but modified so as to overcome 

 certain difficulties experienced. A particular form of bridge was 

 constructed, in which the wire was an air line, and a special form of 

 slider adopted to tap without sagging the wire, so arranged that it 

 could be moved by the observer from the extremity of the bridge, 

 and thus ail thermo- currents due to his proximity were avoided. 



