XI, A, 6 Behrman: Determination of Hardness in Water 293 



The acidity of the sample (due to free carbon dioxide) is 

 first determined with sodium carbonate in the presence of 

 phenolphthalein. If the amount of free carbon dioxide is found 

 to be over 25 parts per million, a fresh 100 cubic centimeter 

 portion is aspirated from five to ten minutes and is used for 

 the remaining determinations. If the acidity is less than 25 

 parts per million, aspiration is unnecessary. The 100 cubic 

 centimeter portion is then titrated with 0.1 N sulphuric acid,^ 

 using one drop of dimethylamidoazobenzene (butter yellow) as 

 indicator. From this titration is obtained, as usual, the "bicar- 

 bonate alkalinity," which may also be taken as a measure of 

 the "temporary hardness" — in both cases, of course, making 

 proper allowance for the normal carbonates. 



A few drops of 0.1 N sulphuric acid are added in excess, 

 and the solution is aspirated for five minutes. One cubic centi- 

 meter of phenolphthalein solution (1 per cent) is then added, 

 followed by 0.1 A'^ alcoholic potassium hydroxide until a slight 

 phenolphthalein coloration can be noted in the yellow produced 

 by the dimethylamidoazobenzene. Titration is then made with 

 0.1 N potassium palmitate solution. The end point taken is 

 not the first faint pink which is observed, but the first intense 

 pink — an end point which can be determined without difficulty 

 after a little practice. From the volume of solution used in the 

 titration the total hardness, expressed in parts per million of 

 calcium carbonate, is calculated. 



It is believed that the degree of accuracy and the rapidity 

 of this determination make the method as outlined above very 

 desirable for the determination of hardness in a commercial 

 laboratory. The calcium may be separately determined and 

 the magnesium obtained by difference, thereby eliminating the 

 tedious gravimetric determination of the latter. 



' Sulphuric acid was employed in place of hydrochloric (as recommended 

 in Blacher's original communication) , because of the possible applicability 

 of the former in the form of sodium bisulphate in field work. 



