VARIABLES OF AQUARIUM WATER 73 



considerably affect experimental conditions. The de- 

 termination of alkalinity sometimes involves two titra- 

 tions rather than one. If the pH of the water is above 

 8.3, phenolphthalein alkalinity is said to be present; 

 whereas, the alkalinity occurring between 4.5 and 8.3 

 is called methyl orange alkahnity. 



Fhenolphthalein Alkalinity 



REAGENTS REQUIRED: (I) Sulfuric acid solu- 

 tion .02N (dissolve 0.6 ml. concentrated H2SO4 [sp. g. 

 1.83] in 200 ml. of distilled water and make up to 1 L.; 

 To standardize weigh out 1.060 g. of reagent grade 

 anhydrous sodium carbonate [Na2C03], dissolve in 

 400 ml. of distilled water and make up to 500 ml. ) . The 

 .02N sulfuric acid is titrated against an equal volume 

 ume (10 or 20 ml.) of the carbonate solution using 

 phenolphthalein as an indicator. The correction fac- 

 tor for the .02N sulfuric acid is calculated by 



(2) Phenolphthalein in- 



ml. of Na2C03 



ml. H2SO4 used in titration. 



dicator (0.5% solution in 50% alcohol). 



TITRATION procedure: Add a few drops of 

 phenolphthalein indicator to 100 ml. of sample. If a 

 pink color appears, titrate with .02N sulfuric acid to 

 an end point where the pink color disappears. The 

 millihters of acid multiplied by 10 and the correction 

 factor equals p.p.m. of phenolphthalein alkalinity ex- 

 pressed as p.p.m. of calcium carbonate. 



Methyl Orange Alkalinity 



REAGENTS REQUIRED: (1) SulfuTlC aCld Solu- 



tion .02N (same as for phenolphthalein alkalinity). 



