198 Phelps — Determination of Nitrites in Absence of Air. 



Art. XVI. — A Determination of Nitrites in Absence of Air / 



by I. K. Phelps. 



[Contributions from the Kent Chemical Laboratory of Yale University — CXXIV.] 



Dunsten and Dtmond* have recommended the use of an evac- 

 uated flask for the estimation of nitrites by the action of potas- 

 sium iodide in acid solution. Under these conditions, the 

 nitrous and hydriodic acids interact to produce nitric oxide 

 (which must be kept from contact with gaseous oxygen) and 

 iodine which is determined by decinormal sodium thiosulphate. 

 As objections to the process may be cited the necessity of get- 

 ting an absolutely gas-tight, rubber-jointed apparatus and the 

 restriction put upon the size of the flask by the two consid- 

 erations of withstanding the atmospheric pressure when evacu- 

 ated and yet being thin-walled enough to allow of the ready 

 heating of the flask. A practical test of a slight modification of 

 the device already used in the determination of nitric acidf 

 for getting an inert atmosphere proves to obviate these diffi- 

 culties and to leave little to be desired in point of accuracy. 



The apparatus used was the same as in the estimation of 

 nitric acid already referred to above. It consisted of a boiling 

 flask of 250 cm3 capacity closed with a rubber stopper carrying 

 in its two perforations the inlet and exit tubes. A stoppered fun - 

 nel of 50 cm3 capacity with its tube constricted at its lower end was 

 used as an inlet tube ; and a glass tube of 'S cm internal diameter, 

 enlarged just above the stopper to a small bulb (to prevent 

 mechanical loss of the solid contents of the flask during the 

 boiling) and bent twice at right angles, served as an exit tube. 

 The flask was supported in the usual manner at a convenient 

 height to allow of heating with a Bunsen burner placed beneath 

 and the exit tube was made of a sufficient length to reach to 

 the surface of some mercury contained in a test tube to the 

 depth of about three centimeters. 



The analysis was made as follows : An amount of standard 

 arsenious acid solution, slightly in excess of that required to 

 take up the iodine to be set free later by the nitrous acid, and 

 25 cm3 of a concentrated solution of sodium carbonate were 

 placed in the flask. The stem of the dropping funnel was 

 completely filled with water, the rubber stopper inserted 

 tightly, and the contents of the flask boiled until all air was 

 expelled — a process requiring an active boiling of 5-8 minutes. 

 The flame was then removed, the exit tube plunged deep into 

 the mercury by changing the position of the flask on its wire 

 gauze — which is particularly easy if the gauze is well depressed at 



* Pharm. Jour. [3], 19, 741. f This Journal, xiv, 440(1902). 



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