86 Messrs. V. H. Veley and J. J. Manley. 



" Some Physical Properties of N itric Acid Solutions." By V. H. 

 VELEY, F.K.S., and J. J. MANLEY, Daubeny Curator, Magdalen 

 College, Oxford. Eeceived February 11, Eead March 7, 

 1901. 



SECTION' I. Introductory. 



The results obtained in our former communication on the " Electric 

 Conductivity* of Solutions of Nitric Acid" have led us to continue 

 our investigations upon other physical properties of the same sub- 

 stance, partly with a view of confirming our conclusions, and partly 

 also because previous observations on firstly, the refractive indices of 

 samples of varied concentration, and secondly, the contractions on 

 admixture of the acid with water, are comparatively few. 



The conclusions, at which we previously arrived, were that the values 

 of the electric conductivities to a less degree, and the electric tem- 

 perature coefficients to a greater degree, varied at percentage points 

 approximately corresponding to the composition required by the 

 hydrates HN0 3 .3H 2 0, HNO a .2H,O, HNOg.H.O, and 2HNO.,.H 2 ; 

 the two latter being the analogues of orthophosphoric H 3 P0 4 and 

 pyrophosphoric acid H 4 PoO; respectively. 



It was further shown that acid of 96 99 '7 per cent, concentration 

 showed remarkable peculiarities, and the suggestion was put forward 

 by others and ourselves that an initial decomposition into water and 

 nitric anhydride takes place. 



In the present work determinations were at first made both of the 

 refractive indices and densities for percentage differences of approxi- 

 mately 5 per cent. ; a rough curve was then drawn, and from any 

 indications given of marked variations of curvature, observations were 

 more especially multiplied on either side of points which might be 

 regarded as critical. 



As regards the division of labour, the former of us is mainly respon- 

 sible for the contraction and analytical determinations, the latter for 

 the optical measurements and the apparatus connected therewith. 



The work was conducted partly in the Chemical Department of the 

 University Museum and partly in the Laboratory of Magdalen 

 College. Lastly we desire to express our thanks to the Government 

 Grant Committee of the Eoyal Society for apparatus purchased or 

 lent ; to the Chemical Department of the University Museum for loan 

 of instruments ; to Mr. E. H. Hayes, of New^College, for assistance in 

 verifying and correcting calculations. 



* 'Phil. Trans.,' A, 191 (1898), 365. 



