374 



Scientific Proceedings, Royal Dublin Society. 



its existence in solution, but the formula assigned to it was 

 H3NO4 * H 2 0. Other four acids were isolated by Erdmann, one of 

 the most interesting being octobasic nitric acid (HO) 4 N ■ ■ N(OH) 4 

 corresponding to crystallized arsenic acid (HO) 4 ■ As * * As(OH) 4 , 

 and to the tetracalcic phosphate obtained from " basic slag." 

 As Erdmann points out, Graham discovered this and two other 

 acids by observing their viscosity or transpiration time through 

 a capillary tube, the flow of the octobasic acid showing a 

 characteristic maximum. (" Chemical and Physical Researches," 

 by Thomas Graham. Edinburgh, 1876, p. 602.) Graham gives 

 the formulae of some copper and bismuth salts derived from the 

 octobasic nitric acid. (Ibid., p. 378.) 



The transpiration time, in seconds, of water is 348 ; of HN0 3 , 

 344-5; of H 3 N0 4 , 705; of H 8 N 2 9 , 732; and of H 5 N0 5 , 712; 

 these figures are very remarkable. Pickering obtained two acids 

 (Chem. Soc. Trans., 1893, 63, p. 436) crystallized, namely, H 3 N0 4 , 

 melting at - 36°-8, and H 5 N0 5 • H 2 0, melting point - 18°-0. 

 These acids were shown to exist at a considerable range of tem- 

 perature above their freezing or melting points, the first H 3 N0 4 

 at 52°, and the second H 5 N0 5 ■ H 2 at 36°. 



Erdmann determined the melting point of the acid HN0 3 , 

 which is not well crystallized, to be - 42° ; and with a special 

 apparatus the boiling point, which was 21°-5 under a pressure of 

 24 mm. of mercury. His results are summarised as follows : — 



