444 Pheljps — Titrimetric Estimation of Nitric Acid. 



how this second error, which is one of deficiency and hence 

 correcting the first error, may have been overlooked. 



Ferrous ammonium sulphate has been recommended by 

 Austin and Chamberlain* and by Rosaf as more convenient, 

 stable, and sensitive than the crystalline ferrous sulphate. It 

 would seem possible that nitric acid might act as an oxidizing 

 agent on the ammonium salt, and certainly nitrous acid (if it 

 were produced, as might be, as an intermediate product in the 

 reduction of nitric acid to nitrogen dioxide) would act accord- 

 ing to the equation, 



NH,Cl + HN0,=HCl + 2Hp + N,. 



Such an action either of the nitric acid or nitrous acid would 

 produce an error of deficiency. Experiments XL and XII were 

 made to test this point, being made exactly like those num- 

 bered I-YIII, except that 1 gram of crystallized ammonium 

 sulphate was added with the ferrous salt. The results show 

 slight bnt appreciable losses. 



The concentration of the hydrochloric acid in this operation 

 does not allow of much diminution under these conditions, 

 where immediate reduction of the nitric acid without any 

 volatilization is a necessity, — a fact which has been recognized 

 before b}^ Roberts and obviated under the conditions there 

 used. 



Thus it would appear — 



First. That the method outlined above is capable of yield- 

 ing very accurate results, affording as it does an easy and com- 

 plete means of shutting out oxygen from the nitrogen dioxide 

 while that gas is in contact with the ferrous salt. 



Second. That prolonging the boiling only until the dark 

 colored compound of nitrogen dioxide with ferrous salt is 

 broken up, results in the incomplete reduction of the nitric 

 acid. 



Third. That ammonium salts must be absent, if the highest 

 accuracy is desired. 



*Amer. Cbem. Jour., v, 209. f Gazz. cMm. ital., xv, 295. 



