INTERACTION BETWEEN SULPHITES AND NITRITES. 285 



pitation occurs during their preparation, and with these, therefore 

 we made an experiment to determine quantitatively wliat happens 

 up to the point when the last portion of hydroxide disappears, a 

 point indicated by rosolic acid losing its pink colour. 



Washed sulphur dioxide was sent in a steady stream into a 

 solution of 11.21 grams real sodium hydroxide and 19.34 grams 

 sodium nitrite in about 198 grams water, kept in active motion 

 and immersed in ice. The sodium compounds were in molecular 

 proportions; more nitrite would not have mattered. In a short 

 time a 10 cc. pipetteful was removed ; soon after a second ; and 

 not very long after a third one, just when the pink colour of the 

 rosolic acid present had disappeared. The three portions were 

 treated alike. Each was mixed with excess of solutions of am- 

 monium and barium chlorides and the precipitate filtered off, 

 oxidised to sulphate, washed with dilute hydrochloric acid, and 

 weighed as barium sulphate. The ammonium-chloride filtrate 

 was evaporated to dryness, during which operation all the sul- 

 phur of the sulphazotised salts was converted to sulphate by the 

 nitrite and ammonium chloride. The soluble salts were washed 

 out with dilute hydrochloric acid, and the barium sulphate 

 collected and weiohed. The solution of salts removed from the 

 barium sulphate was concentrated and then heated under pressure 

 for hours, after which it was found to be still clear and there- 

 fore free from sulphate, which must have formed by hydrolysis 

 had any sulphazotised salt escaped decomposition during the 

 evaporation with nitrite and ammonium salts. 



We give the quantities of sulphur dioxide found in each 

 pipetteful as sulphite and as sulphazotised salts, and also state 

 these quantities as parts per iiundred of the total sulphur dioxide 

 which had entered it. 



