OF ARTS AND SCIENCES. 275 



XVIII. 



CONTRIBUTIONS FROIVI THE CPIEMICAL LABORATORY OF 



HARVARD COLLEGE. 



THE VOLUMETRIC DETERMINATION OF COMBINED 



NITROUS ACID. 



By Leonard P. Kinnicutt and John U. Nkf. 



Presented May 9th, 1883. 



The amount of nitrous acid contained in commercial samples of 

 potassic and sodic nitrites has been commonly determined in the fol- 

 lowing manner. The nitrites are dissolved in slightly acidulated 

 water ; a solution of potassic permanganate is added till the oxidation 

 of the nitrous acid is nearly completed; the solution is then made 

 strongly acid, and potassic permanganate added until the solution has 

 a faint red color. 



This method is far from satisfactory, closely agreeing results being 

 rather the exception than the rule. The cause is most probably due 

 to the escape of a small amount of nitrous acid, and also to the slow 

 oxidation of the last traces of the nitrous acid by the potassic per- 

 manganate. 



A further study of the analyses of nitrites volumetrically seemed 

 desirable, and after numerous experiments the following process, or 

 modification of the old process, as it might more properly be called, 

 was devised. 



The sample of nitrite is dissolved in cold water, one part of the 

 salt to at least three hundred parts of water. To this solution a deci- 

 normal solution of potassic permanganate is added, drop by drop, till 

 the liquid has a decided and permanent red color, then two or three 

 drops of dilute sulphuric acid, and immediately afterwards an excess of 

 the potassic permanganate solution. The liquid, which should now be 

 of a dark red color, is made strongly acid with sulphuric acid, heated to 

 boiling, and the excess of potassic permanganate determined by means 

 of a deci-normal solution of oxalic acid. 



