ESTIMATION OF CARBONATES AND BICARBONATE^ 282 



An attempt was made, using a modification of Winkler's method 

 as described by F. K. Cameron, 1 but even on the same solution 

 no two results were alike. 



The cause of the varying inaccuracies is the high temperature 

 of Calcutta in the hot weather. It is possible however to work 

 Winkler's method in the cold weather. 



In the hot weather temperatures of 80° or 90°, perhaps even 

 100° Fahrenheit, the standard solution from the burette, when 

 admitted slowly into the liquid causes local supersaturation, and 

 some C0 2 inevitably escapes, before all the carbonate has been 

 converted into bicarbonate. 



In estimating the bicarbonates and carbonates, I followed very 

 closely the method adopted by F. K. Cameron, using very small 

 quantities of indicator, titrating to the first change of colour of the 

 methyl orange, and to complete loss of colour of the phenolphthalein. 

 I modified his method in the following manner :- 



Using a burette, not fitted with a glass stop-cock, a rubber tube 

 of V bore about 16 inches long was fastened to the end of the burette. 

 The lower end of the rubber tube was fitted with a glass nozzle. 



An Erlenmeyer flask of 350 c. c. capacity was now fitted with a 

 rubber cork in which two holes were drilled close together. Through 

 one hole the glass nozzle which conveys the liquid from the burette 

 was inserted. Through the other was inserted a short piece of 

 glass tube, about two inches long, of which about f inch protruded 

 from the top of the cork. This was fitted with a short piece of 

 rubber tubing about 2\ inches long. 



A large pinch-cock was now fitted, so that it controlled both the 

 rubber tube from the burette, and the short rubber tube fitted 

 to the short glass tube which passes through the rubber cork. The 

 burette was now filled with standard KHS0 4 , and the liquid to be 

 titrated was placed in the Erlenmeyer flask. The cork was fitted, 

 and the standard solution admitted slowly. Every now and then 

 the pinch-cock was closed, whereby the flask was completely sealed 

 and the flask was rotated with a circular motion. In this way 

 any CO* which has escaped into the air inside the flask is not lost, 

 but is re-absorbed into the liquid so long as any normal carbonate 

 remains. Absorbtion is aided by the warm temperature of the 

 laboratory. 



i F K Cameron. « Estimation of Carbonates and Bicarbonates in Aqueom 

 Solution", V, S. Dept. of Agriculture, Div. of Soils, Bull. 118 .1901. 



