XIII, A, 1 Heise and Behrman: Water Analysis in Field H 



case, after an excess of silver nitrate has been provided, more 

 water is added from the cylinder until the rose color is entirely- 

 displaced by a bright yellow, corresponding to the shade used 

 in standardization. Check determinations may be made as be- 

 fore by adding more pellets and titrating. 



If, to react with a half of a "weak" tablet (a whole tablet 

 being equivalent to 0.96 milligram of chlorine), there were 

 required 76 cubic centimeters of the water under examination, 

 the chlorine content, expressed in parts per million of chlorine, 

 would be found from the expression 



p, 1,000 X 0-5 X 0-96 - _ 

 U= ^ =6.3. 



Total hardness. — The pellets of potassium palmitate used for 

 the determination of hardness are made from a pill mass of 

 glucose and potassium palmitate. One hundred grams of glucose 

 are used with an amount of potassium palmitate correspond- 

 ing to 15 grams of palmitic acid. To make potassium palmitate, 

 palmitic acid is dissolved in alcohol and neutralized with normal 

 alcoholic potash solution, using phenolphthalein as indicator. 

 The resulting alcoholic solution is then evaporated to dryness. 

 The residue may be used without further treatment for making 

 the pellets. 



The following method is employed for the standardization 

 of the pellets: A saturated solution of calcium hydroxide is 

 prepared from pure calcium oxide. The normality of this is 

 determined by titration of 25 cubic centimeters with 0.1 A*' 

 sulphuric acid, using phenolphthalein as an indicatoi\ One 

 hundred cubic centimeters of the calcium hydroxide solution 

 are then pipetted into a 200 cubic centimeter volumetric flask. 

 A few drops of phenolphthalein solution are added, followed by 

 normal sulphuric acid to acid reaction. Alcoholic potash (0.2 

 N) is then added, drop by drop, until a faint pink is produced. 

 Distilled water that has previously been boiled to expel carbon 

 dioxide is added to the mark. 



The calcium sulphate solution thus prepared is used to stand- 

 ardize the pellets. Five of these, crushed in a mortar with a 

 little distilled water, and 5 drops of phenolphthalein are added. 

 The standard calcium sulphate solution is then added from a 

 burette, until the last trace of phenolphthalein pink disappears. 

 From the number of cubic centimeters used, and the determined 

 strength of the calcium hydroxide solution, the strength of the 

 pellets, expressed in term of calcium carbonate, is calculated. 



Since a saturated solution of calcium hydroxide is about 0.04 



