CARBONATES AND BICARBONATES 87 



"One portion of the solution will serve for the determina- 

 tion of both carbonate and bicarbonate. The method 

 depends upon the different actions of phenolphthalein 

 and methyl orange in the neutralization of these two 

 substances. Potassium hydrogen sulphate solution is 

 used for titrating, the first step being the phenolphthalein 

 as indicator. The reaction is expressed by the following 

 equation : 



Na 2 C0 3 + KHSO4 = KNaS0 4 + NaHC0 3 . 



The point of neutrality is shown when all carbonate present 

 is converted into bicarbonate. The second step is the 

 titration of the bicarbonate formed in the first step to- 

 gether with that existing originally in the solution, using 

 methyl orange as indicator. This reaction is expressed 

 by the following equation: 



NaHC0 3 + KHSO4 = KNaS0 4 + H 2 C0 3 . 



The point of neutrality is shown in this case when all 

 bicarbonate has been decomposed." The total titration 

 for bicarbonate, less the titration for the carbonate, gives 

 the titration for the bicarbonate originally present. 



This and certain other methods for determining car- 

 bonates does not always prove satisfactory as it does not 

 distinguish between the sodium and the noninjurious 

 calcium and magnesium salts. 



The New Mexico Station uses the above method for 

 determining the carbonates, but also determines the 

 calcium and magnesium and combines these bases with 

 carbonates before determining the sodium salts of the 

 carbonate radical. With the exception that sulphuric 

 acid is used in the place of potassium acid sulphate and 

 that methyl orange is the indicator, this is also one of the 

 methods used in Utah. 



