xni. A, 1 Behrman: Determination of Hardness of Water 23 



aspirated, and neutralized, exactly as in the first method. The 

 liquid, thus prepared, is returned to the 100 cubic centimeter 

 cylinder, and the volume is noted with the aid of graduation 

 marks, etched on the cylinder at 1 cubic centimeter intervals to 

 105 cubic centimeters. The volume of the liquid should be read 

 to the nearest 0.5 cubic centimeter. This will be usually found 

 to be between 102 and 105 cubic centimeters. 



In a small (100 cubic centimeter), heavily glazed porcelain 

 mortar two or three pellets of potassium palmitate are crushed 

 with 10 or 15 cubic centimeters of water from the cylinder. If 

 an excess of the reagent is not indicated by the characteristic 

 phenolphthalein coloration, more pellets are added until this 

 condition is reached. More water is then added from the cylin- 

 der, slowly and with constant stirring, until the phenolphthalein 

 coloration completely disappears, giving place to a creamy or 

 yellowish white (depending on the amount of methyl orange 

 absorbed during acidification). The end point is sharp and is 

 easily determined. The volume required for the first end point 

 is noted, reading to the nearest 0.5 cubic centimeter. Several 

 more pellets are then added, preferably using the same number 

 as before. Water is again supplied from the cylinder, until a 

 second end point is obtained, and the amount used is noted. 

 The two volumes should check within 0.5 cubic centimeter in 

 fairly hard waters. Where a slightly larger difference is found, 

 the mean of the two determinations may be employed in cal- 

 culating the total hardness.^ 



PREPARATION AND STANDARDIZATION OF POTASSIUM 

 PALMITATE TABLETS 



Potassium palmitate being unavailable, it was prepared by 

 the neutralization of an alcoholic solution of purified palmitic 



' The volume used in the determination is reduced to the volume of the 

 original water, that is, before being diluted with acid, indicator, and alkali. 

 The total hardness is then calculated from this corrected volume of water 

 and from the number and strength of potassium palmitate tablets employed 

 in the determination. Thus, if a 100 cubic centimeter portion of a given 

 water was diluted to 103.5 cubic centimeters before treatment with potassium 

 palmitate, and if, of this diluted volume, 42.5 cubic centimeters were re- 

 quired to react with 4 pellets of potassium palmitate, each equivalent to 2.0 

 milligrams of calcium carbonate, the total hardness, expressed as parts per 

 million of calcium carbonate, would be found from the following expression : 



^ , , ^ 10 X 103.5 X 4 X 2.0 ^^^ 



Total hardness = = 195. 



42.5 



