8 The Philippine Journal of Science i9i8 



The volume of water used in the titration is noted, readings 

 being taken to the tenth of a cubic centimeter. Two or three 

 more pellets are added, followed by more of the water to the 

 second end point. 



The alkalinity, expressed as parts per million CaCOg, is readily 

 calculated from the number and strength of pellets and the 

 volume of water used in the determination. Thus, if 4 pellets 

 of sodium bisulphate, each equivalent to 1.10 milligrams of 

 calcium carbonate, require 22.4 cubic centimeters of the water for 

 interaction, the alkalinity will be 



1,000 X 4 X 1.10 .Q. 

 22.4 =^^^ 



and would be reported as 200 (that is, in terms of two significant 

 figures) . 



Normal carbon/ites. — If normal carbonates (or hydroxides) 

 are present, the water will give a pink coloration with phe- 

 nolphthalein. In this event the amount of normal carbonates is 

 determined with pellets of sodium bisulphate. The procedure 

 is identical with that for the determination of alkalinity, except 

 that 5 drops of phenolphthalein indicator solution (1 per cent 

 alcoholic) are used instead of the 1 drop of butter yellow. Where 

 the normal carbonates are present only in small amount, half, 

 or even a quarter, of a pellet may be all that can be used. 



As phenolphthalein is sensitive to carbonic acid, the end point 

 in this determination is reached when only half of the alkali 

 is neutralized. Accordingly the same sodium bisulphate pellet 

 that was equivalent to 1.10 milligrams of calcium carbonate 

 in the determination of alkalinity will be equivalent to twice 

 that amount, or 2.20 milligrams, when used in the determination 

 of normal carbonates. 



Thus, if 2 of these pellets required 57 cubic centimeters of 

 the water for the reaction, the results expressed in parts per 

 million of calcium carbonate would be 



1,000 X 2 X 2.20 _„„ 



57 ~ • • 



When, as is usually the case with Philippine waters, the 

 phenolphthalein alkalinity is less than half that determined with 

 butter yellow, the alkalinity of a natural water is caused by 

 bicarbonates and normal carbonates and is equal to their sum. 

 If, therefore, no normal carbonate is present, the alkalinity is 

 numerically equal to the bicarbonates, when both are expressed 

 in terms of calcium carbonate. If, when normal carbonates 

 are present, the alkalinity is found to be equal to the normal 

 carbonates — that is, when the phenolphthalein titration is one 



