INTERACTION BETWEEN SULPHITES AND NITRITES. 295 



potassium or sodium sulphite gives off carhoii dioxide to n cur- 

 rent of decarbonated air much to the same extent as when dis- 

 solved alone in water. But sodium acid-carbonate may be added 

 to an ice-cold solution of sodium pyrosulphite, containing also 

 much normal sulphite, and be only very gradually decomposed 

 with effervescence. Indeed, an ice-cold concentrated solution 

 of normal sodium sulphite will deposit some acid-carbonate when 

 charged with carbon dioxide. 



It is, therefore, not surprising that sodium or potassium 

 acid-carbonate has a very marked action upon mixed normal 

 sulphite and nitrite. When the three salts are left together in 

 solution in a closed vessel for a d;iy or two, much sulphazotised salt 

 is formed, so that after carbonate and excess of sulphite have 

 been precipitated by baryta and barium chloride in presence of 

 ammonium chloride, the filtrate from the precipitate when boiled 

 with acid gives much barium sulphate and reduces cupric hydr- 

 oxide freely. The interaction of the salts may be expressed 

 by tlie equation-KNO., + 2K,S03 + 3KHC0, =KoHNS A + -SKoCO, 

 + OH2, but since the two-thirds normal hydroximidosulphate is 

 to a small extent converted by normal carbonate into a more 

 nearly normal salt and acid -carbonate (this Journal, 7, 32), 

 the change expressed by the above equation cannot proceed to 

 completion. 



III. — e. Action of Sulphur Dioxide upoji Normal Carbonate 



and Nitrite. 



When sulphur dioxide is added to two mois, nitrite and one 

 mol. normal carbonate until the solution becomes acid to lacmoid 

 paper, the only products are hydroximidosulphate and carbon 

 dioxide. This was long ago pointed out by us, and also that 



