EXAMINATION OF HYDROGEN DIOXID SOLUTIONS. 9 



hydrogen clioxid. In order to check the permanganate-sulphuric 

 acid method for determining hydrogen peroxid and compare it with 

 other standard methods, it was decided to analyze the samples by 

 three additional methods, namely, the iodin method and the gasomet- 

 ric methods, using sulphuric acid and potassium permanganate in one 

 case and manganese dioxid and sulphuric acid in the other. In each 

 case the hydrogen dioxid solution was measured out and weighed as 

 before stated and aliquots used for the determinations. The iodin 

 method proposed by Rupp was carried out as follows: 



Iodin method. Place 1 gram of potassium iodid in a 250 cc Erlenmeyer flask, add 

 10 cc of 10 per cent sulphuric acid, and as soon as the salt is dissolved run in 10 cc of 

 the diluted peroxid solution, 1:10, by means of a burette. Cover the flask with a 

 watch glass and allow it to stand for 30 minutes. Then add about 200 cc of distilled 

 water and titrate the liberated iodin with tenth-normal sodium thiosulphate solution, 

 using starch solution as indicator. 



This procedure proved somewhat less satisfactory than the phar- 

 macopoeia! method, being less rapid and giving less concordant re- 

 sults. Each assay was made in duplicate and the mean result is 

 given in the accompanying table in the column headed " Iodin 

 method." 



Tins determination was next made by measuring the volumes of 

 oxygen liberated by means of manganese dioxid and potassium per- 

 manganate, respectively, in the presence of sulphuric acid. It was 

 found that Lunge's nitrometer, with a two-way stopcock did not 

 give satisfactory results when the reaction took place inside of the 

 instrument. After making a number of experiments, the following 

 apparatus and procedure were adopted: 



Manganese dioxid method. The apparatus consists of a 50 cc side-arm distilling 

 flask closed with a perforated rubber stopper, through which the delivery stem of a 

 glass-stoppered burette has previously been passed. The side arm of the flask is 

 connected to the nitrometer by means of tightly fitting rubber tubing of any con- 

 venient length and securely wired at each end to prevent leakage. The burette is 

 fastened loosely in a Bunsen clamp in such a manner that the burette and flask can 

 be shaken freely in one plane. The nitrometer is filled with water, the level adjusted, 

 and the determination made as follows: Place about 1 gram of finely powdered man- 

 ganese dioxid in the side-arm flask and add 10 cc of 10 per cent sulphuric acid. Dilute 

 10 cc of the hydrogen peroxid solution to be tested to 100 cc and place a portion in the 

 burette. After sufficient of the solution is run out to fill the delivery stem of the 

 burette fit the stopper (with attached burette) snugly into the neck of the generating 

 flask, and adjust the level of the water in the nitrometer so as to equalize the pressure 

 within the system. Allow 10 cc of the diluted dioxid solution to run slowly into the 

 generator through the burette. After shaking the flask to liberate the dissolved 

 oxygen as completely as possible again adjust the level and note the temperature 

 and pressure. A correction of 10 cc (the volume of solution run into the generator) 

 is subtracted from the reading, and the remainder reduced to 760 mm pressure and 

 20 C. temperature. 



a Archiv. Pharm., 1900, 288: 166. 

 21450 Bull. 15012 2 



