Roberts — Reduction of Nitric Acid by Ferrous Scdts. 131 





With potassium 



I. 



iodide in the Will and Varrentrapp tube 







Vol. of 



Per ceut from 



Per cent from 







miabsorbed gas. 



total vol. 



absorbed vol. 



Iodine. 



(1) 



•45 cm 3 



9998 



98-1 



•0004 



(2) 



•65 



99-83 



96-74 



•0008 



(3) 



•45 



100-3 



97-6 



•0004 



(*) 



•6 



99-7 



97-7 



•0022 





With if a 



II. 



ter in Will and V 



'arrentrapp tube. 





(1) 



•6 



97-76 



95' 







(2) 



•6 



97-76 



95-2 







(3) 



•6 



97-9 



95'2 



, 



(*) 



•6 



97-4 



94-7 







(5) 



2'43 



97'3 



87* 







It will be seen by a glance at the tables that the best ana^ 

 lytical results are obtained by the use of potassium iodide in 

 the Will and Varrentrapp tube and calculation from the total 

 volume of gas. The average of the results obtained above, 

 omitting for a reason which will appear later the last experi- 

 ment of the second series, may be expressed in this way : 



With KI. With water. Difference. 

 Per cent from total gas 99*95 97'7 2'25 



" "nitric oxide 97'53 95*0 2'53 



Diff. 2-42 2*7 



In each case there is an amount of gas equal to about 2*5 

 per cent of the total volume which is not nitric oxide. In 

 whichever way reckoned the total amount of gas collected is 

 about 2*5 per cent greater when potassium iodide is used than 

 when water is used in the Will and Varrentrapp tube. This 

 would indicate that some higher oxide of nitrogen is formed 

 and is decomposed by the potassium iodide with a liberation of 

 nitric oxide equal to about 2 -5 per cent of the total volume of 

 gas. In case the formation of this oxide were due to traces of 

 air which oxidized the nitric oxide to nitrous acid, the volume 

 of nitrogen thus left would be, as has been shown, exactly 

 equal to that of the nitric oxide oxidized, and therefore there 

 should be about 2*5 per cent of gas incapable of absorption by 

 potassium permanganate, which is practically found to be the 

 case. This would furnish, then, a simple explanation of the 

 results given. Supposing this explanation to be the correct 

 one, the presence of air should not influence the total volume 

 of gas in case potassium iodide is not used. To test this point, 

 the last experiment of the second series was performed. This 

 experiment was done in exactly the same way as the others 

 except that the carbon dioxide was not allowed to pass through 

 long enough to displace the air completely. It will be observed 

 that the total volume of gas is practically the same as in the 



