METHODS OF ANALYSIS. 19 



CARBON DIOXID (GIVEN OFF FROM THE BICARBONATES WHEN THE WATER IS EVAPO- 

 RATED TO DRYNESS). 



In making this determination the method of Cameron a for the esti- 

 mation of carbonates and bicarbonates in aqueous solution was used. 

 By this method the amount of bicarbonic acid ions (HCO 3 ) present was 

 determined, and from this an estimation made of the amount of bicar- 

 bonic acid that would remain as normal carbonate and the amount 

 that would be given off as carbon dioxid. The method is as follows: 



To 100 grams of the water add a few drops of phenolphthalein. In 

 case there are alkali carbonates present the usual red color will be 

 evident. The solution is now titrated with a twentieth normal solution 

 of acid potassium sulphate (HKSOJ, adding a drop every two or three 

 seconds, until the red color has completely disappeared. The reading 

 on the burette is recorded, and to the clear solution one drop of methyl 

 orange is added. A pure yellow color results. The titration is con- 

 tinued with HKSO 4 , without refilling the burette until the change to 

 a very slightly darker and reddish color is noted. The change is faint 

 and practice is required to detect it. The reading at this point is also 

 recorded. 



The first reading recorded gives the amount of alkali carbonates 

 present, and must be multiplied by the factor 0.002979 for the results 

 in grams of CO 3 ions. 



For the number of grams of bicarbonic acid (HCO 3 ) ions present 

 the first recorded reading is multiplied by two and the result sub- 

 tracted from the second reading, and this remainder is multiplied by 

 the factor 0.003028. 



Having now obtained the weight of HCO 3 in 1,000 grams of water, 

 calculate the weight of CO 2 given off when a like amount is evapo- 

 rated to dryness, and dividing this result by the weight of 1 cc of 

 carbon dioxid at C. and 760 mm pressure, the number of cubic cen- 

 timeters of carbon dioxid given off 'from the bicarbonates is obtained. 

 Subtract the number of cubic centimeters of carbon dioxid given off 

 from the bicarbonates from the number of cubic centimeters of carbon 

 dioxid in excess of that necessary to form normal carbonates, and the 

 result is the number of cubic centimeters existing in solution in a 

 free state. 



BICARBONIC ACID. 



The amount of this substance present in the spring was estimated 

 during the process of determining the amount of carbon dioxid given 

 off from bicarbonates in the preceding paragraph. 



o Report 64, U. S. Dept. Agr., Field operations of the Division of Soils, 1899; Amer. 

 Chem. J., 1900, 23:471. 



