128 Some Physical Properties of Nitric Acid Solutions. 



The general conclusions are that, 



(1.) Both the deflectable and undeflectable rays give relative con- 

 ductivities nearly, but certainly not quite, equal to the relative 

 densities. 



(2.) All the different kinds of undeflectable rays give the same rela- 

 tive conductivities, but the deflectable rays give somewhat different 

 relative conductivities. 



Both these kinds of rays are in this respect sharply distinguished 

 from Bontgen rays, which give relative conductivities several times 

 greater than the relative densities in the case of gases containing 

 sulphur or the halogens. 



" Some Physical Properties of Nitric Acid Solutions." By V. H. 

 Veley, F.B.S., and J. J. Manley, Daubeny Curator, Magdalen 

 College, Oxford. Beceived February 11, — Bead March 7, 

 1901. 



(Abstract.) 



The results obtained by the authors on the electric conductivity of 

 solutions of nitric acid have led them to continue their investigations 

 on other physical properties of the same substance with a view of con- 

 firming the conclusions drawn therefrom. 



In the present paper the properties examined are the densities, with 

 especial reference to the contractions, and the refractive indices. 



The various sources of error and their possible magnitude are dis- 

 cussed in full : for the densities, those of analysis, unavoidable in this 

 case, temperature, errors of filling pyknometers both with acid and 

 water ; for the refractive indices, those of micrometer screws, divided 

 circle, parallelism of quartz plates are more especially alluded to, as 

 also the several effects likely to be produced by the various substances 

 with which the acid solutions of necessity came into contact. The 

 results obtained by both methods are given in a series of tables, and 

 compared with those calculated from various equations for straight 

 lines. These show that the physical properties are discontinuous at 

 points corresponding very approximately to the concentrations required 

 for simple molecular combinations only of nitric acid and water. In 

 the case of the densities and contractions, the best defined points of 

 discontinuity correspond to the composition of the hydrates with 14, 7, 

 4, 3, 1*5, and 1 molecular proportions of water; in the case of the 

 refractive indices, the most marked points correspond to the 14, 7, and 

 1*5 hydrates. 



The results for the contractions further confirm those for the electric 

 conductivities as to a remarkable discontinuity at concentrations 95 per 



