306 Mr. Griffin on the Constitution of 



Observations on the Table of Nitric Acid. 



The greatest chemical strength of nitric acid in solution is 

 1348^°. This constitutes the protohydrate of sp. gr. 1*521. 

 The volume of a test atom of acid, as it exists in this hydrate, 

 is 58*09 septems. The condensation which occurs in diluted 

 solutions extends to 31 septems per test atom in a solution 

 of 1°, where the dilution is 1348 fold. Both as respects so- 

 lubility and power of condensation, nitric acid stands between 

 sulphuric acid and muriatic acid. 



The fraction which + 1 indicates the mean specific gravity 

 of 100° of nitric acid is (-6651 •*■ 17'216 = ) '038634. 



Table VII. Showing the increase of Specific Gravity occa- 

 sioned in Solutions of N 2 O 5 by condensation. 



The point of greatest density in the hydrates of nitric acid 

 coincides with that of greatest chemical strength, namely, in 

 the protohydrate. The hydrate that distils without alteration 

 in constitution is N 2 O 5 , 4H 2 O. The hydrate that sustains 

 the greatest amount of condensation is N 2 O 5 , 8H 2 O. 



Messrs. Play fair and Joule's account of the atomic volume 

 of nitric acid is as follows (Phil. Mag., vol. xxvii. p. 521) : 

 — "Nitrate of water in the acid of sp. gr. 1*42 seems to affect 



four volumes Nitrate of water calculated on weak acids 



has three volumes ; but there being no good fixed point upon 

 which to make the calculation, we must leave at present this 

 point undetermined." 



This estimate of the atomic measure of the acid in solution 

 of sp. gr. 1*42 is nearly correct. Four volumes for the hy- 

 drate is three volumes for the anhydrous acid, and 3 x 16*07 

 = 48*21, while the number given in Table VI. is 49*10 sep- 

 tems. Three volumes is also correct for the hydrate in a 

 single weak solution ; for 16*07 x 2 = 32*14 septems is nearly 

 the atomic measure of the anhydrous acid in a solution of 4°. 

 But there is no sudden fall in the atomic volume from 4 to 3, 

 nor do these numbers apply to any solutions save the two 

 that are named specially. They are only separate links of a 

 long chain, whose parts are all of different magnitudes. 



