4-36 Dr. Schcenbein on the relation of Ozone to Hyponitric Acid. 



acid does not give rise to the reactions described. The cause 

 of those effects must therefore be sought in another substance, 

 and both hyponitric and nitrous acid not being able to co- 

 exist with free water, we are not allowed to consider either 

 the one or the other of those acids as that cause. As I have 

 already remarked, the reactions in question can, according to 

 my opinion, only be accounted for in a satisfactory manner 

 by admitting the presence of N0 2 + H0 2 in the acid mixture 

 so often mentioned. My experiments have further shown 

 that iodide of potassium, be it solid or dissolved in water, is 

 readily decomposed by ozone, iodine being eliminated. In 

 putting our acid mixture to a solution of the salt mentioned, 

 deutoxide of nitrogen is abundantly disengaged, iodine preci- 

 pitated, and nitrate of potash formed. As pure nitric acid 

 containing as much water as the said acid mixture, does not 

 act upon the solution of iodide of potassium, it cannot be the 

 nitric acid of our mixture that causes those phsenomena, nor 

 can they, from reasons already stated, proceed from hypo- 

 nitric or nitrous acids. 



If we admit that there is, besides nitric acid, some N0 2 

 + H0 2 present in the acid mixture, I think we may easily 

 account for those reactions. H0 2 oxidizes the potassium of 

 the iodide, nitric acid unites with the base thus formed, and 

 NO a is set free. 



(N0 4 + H0 2 ) + (NO, + H0 2 ) + PI = PO N0 5 (P0 2 N0 4 ) 



+ I + N0 2 + HO. 



The facts I am about to state are most likely also connected 

 with the subject under discussion. 



Largely diluted pure nitric acid, not colouring in the least 

 paste of starch containing chemically pure iodide of potassium, 

 when put for a short time in contact with a number of metals, 

 as zinc, iron, lead, copper, mercury, silver, &c, acquires the 

 property — 1. To colour deeply blue the paste mentioned. 

 2. To transform the yellow cyanuret into the red one. 3. To 

 colour blue the resin of guaiacum. 4. To decompose sul- 

 phui'etted hydrogen, &c. 



Tin is an exception to the rule, for however long dilute 

 nitric acid may have been in contact with that metal, it does 

 not cause the reactions indicated. On the contrary, an acid 

 having the properties mentioned, loses them when mixed in 

 proper quantities with dilute nitric acid which has been in 

 contact with tin. The latter acid has also the power of dis- 

 charging the colour of paste of starch rendered blue by iodine. 

 From the facts stated, it seems to follow, that when dilute ni- 

 tric acid is acted upon by oxidable metals, the same oxidizing 



