The present paper deals with a modified procedure for determination of hardness of water according to the soap method.
Pour 10 cc of a sample water into an aeration vessel shown in Fig. 1. Titrate with the soap solution while being bubbled by an air diffuser which is made of either sintered glass or silk cloth. Finsh the titration when the formed lather will completely cover the surface for one minute after stopping the aeration.
The determination of hardness of barum. chloride solution according to the micro and the macro procedures showed concordant values between these two procedrues. In case of a calcium salt solution, a linear relation exists between the titer and the hardness over a hardness-range between 1 and 8. In case of magnesium sulfate solution, a noticeable discrepancy has been observed between the experimental and the theoretical. It has been found, however, that his abnormality can be removed by the addition of ethyl alcohol. A greater value for hardness of about 10 per cent was obtained in an equal mixture of calcium and magnesium sulfate. The values for hardness of various fresh waters obtained according to the micro procedure showed in average a deviation of about 8 per cent from values for total hardness calculated from calcium and magnesium contents.