Some Physical Properties of Nitric Acid Solutions. 87 



II. Arguments of Former Writrrs, 



Mendeleef * from results, the source of which id not quoted, has put 

 forward three equations to represent the densities d in terms of 

 percentage p as follows : 



From to 41 -2 per cent. (HN0 3 511,0) : 



d = 



From 41 -2 to 63 -63 per cent. (HN0 8 211,0) : 

 d = 9570 + 84-18p-0-24;A 



d = 



From 63-63 to 100 per cent. : 



d = 1 0652 + 62-08^-0-1 G/. 



(Density of water at 4 = 10000.) 



It was found, however, that the differences between the observed 

 and calculated values were greatly in excess of those which could be 

 accounted for by errors of observation. Pickering,! by the application 

 of curves to the results of BerthelotJ for the heats of the dissolution 

 and of Kolb for the specific gravities, deduced the existence of and 

 isolated in a crystalline form the two hydrates HNOsSHoO and 

 HN0 3 .H20. He also alludes to a minor alteration of properties at 

 18 20 per cent., but without drawing any conclusions therefrom, and 

 to the fact that the maximum contraction coincides with the composi- 

 tion of a definite hydrate. 



III. Purification of Materials and Preparation of Stock Samples. 



The methods of purification have been fully described in our previous 

 communications, and our experience has as yet pointed to no improve- 

 ment, though we have had occasion from time to time to confirm the 

 observations of others, working at other times and places, as to the 

 persistent retention of some ammoniacal compound in ordinary distilled 

 water. 



Continued experience has shown that by the methods adopted for 

 the purification of nitric acid, the amount of nitrous, sulphuric, and 

 halogen acids did not exceed 1, 4, and 3 parts per million respectively, 

 quantities which may fairly be presumed to have no effect upon the 

 physical constants. 



* 'Principles of Chemistry,' Eng. Trans. (2nd ed.), vol. 1, p. 272. 

 t ' Journal of the Chemical Society,' 1893 (Trans.), pp. 436-443. 

 J ' Chimie Mecanique,' 1, p. 397. 



H 2 



