Page:Proceedings of the Royal Society of London Vol 69.djvu/94

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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 Royal 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.