128 Roberts — Reduction of Nitric Acid by Ferrous Salts. 



served decrease in volume, for the nitrogen in dissolved air 

 would naturally still remain dissolved without relation to the 

 disappearance of dissolved oxygen. If the deficiencies ob- 

 served in Schloesing's process are due at all to oxidation of the 

 nitric oxide, it is natural to suppose that such oxidation must 

 take place during the passage of the gas from the evolution 

 flask to the mercurial receiver, but in the processes which 

 involve the collection of the gas over aqueous caustic alkali 

 oxidation might readily be brought about by dissolved oxygen, 

 and in this case the nitric oxide removed would not be re- 

 placed by nitrogen. The last mentioned source of error, 

 Glaser* has recently proposed to correct by collecting the gas 

 over a solution of potassium iodide instead of over caustic 

 soda. 



The deficiency in the total volume of gas may also be caused 

 partially or wholly by the solubility of nitric oxide in caustic 

 alkali. Waringtonf has shown that caustic soda is capable of 

 slowly absorbing nitric oxide, and Russell and Lapraik^: state 

 that upon long standing over caustic soda, nitric oxide is decom- 

 posed into nitrous acid, nitrous oxide, and nitrogen. 



Errors of the same sort and in the same direction as those 

 produced by the action of caustic alkali, either alone or with 

 dissolved air, or of air in the apparatus, would be the natural 

 consequence of a failure of the ferrous salt to effect decom- 

 position exactly according to the assumed reaction. Incom- 

 pleteness of decomposition of the nitric acid, or the formation 

 of an oxide of nitrogen higher than nitric oxide would result 

 in producing too small a volume of nitric oxide, and so also 

 would the over reduction of the nitric oxide to nitrous oxide 

 or nitrogen. We have, moreover, abundant evidence on the 

 one hand both of the incompleteness of decomposition of nitric 

 acid, and of the production of a higher oxidation product by 

 the action of the ferrous salt under modified conditions, and, 

 on the other hand, the statement of Carius§ that prolonged 

 contact of nitric oxide with ferrous sulphate induces further 

 reduction of the nitric oxide. Thus, Abel and Eloxam|| found 

 that when the nitrate was introduced into a boiling solution of 

 ferrous sulphate containing an excess of sulphuric acid, nitrous 

 acid was evolved, and some nitric acid remained unaltered even 

 after prolonged boiling ; and EderT after demonstrating (at least 

 inferentially from analytical results) that practically complete 

 decomposition to nitric oxide results when the nitrate is put 

 into a strongly acid and cold solution of ferrous sulphate in 

 excess, and the heating made gradual, showed that under con- 

 ditions otherwise similar excepting that the mixture was boil- 



*Zeitschr. fur Anal. Chem., xxxi, 285. f Journ. Chem. Soc , xxxvii, 4*76. 

 \ Jourri. Chem. Soc, xxxii, 35. § Arm. Chem. u. Pharm., xciv, 138. 



| Journ. Chem. Soc., ix, 97. "j[ Zeitschr. fur Anal. Chem., xvi, 26*7. 



