NOTE ON THE BLACHER METHOD FOR THE DETERMINATION 

 OF HARDNESS IN WATER ^ 



By A. S. Behrman 



{From the Laboratory of General, Inorganic, and Physical Cheraistry, 



Bureau of Science, Manila, P. I.) 



Because of the large amounts of free carbon dioxide and 

 sodium chloride often found in Philippine waters, a study was 

 made of the influence of these substances in the determination of 

 hardness of water by the Blacher method," as such data are not 

 available in the literature. Attention was also directed to cer- 

 tain details of manipulation. Briefly summarized, the results of 

 this study were as follows : 



1. Effect of free carbon dioxide. — The presence of large 

 amounts of free carbon dioxide causes incorrect results in the 

 determination of temporary hardness, as well as an indistinct 

 end point, with correspondingly incorrect results, for the "total 

 hardness." Satisfactory results were obtained with concentra- 

 tions as high as 28 parts of free carbon dioxide per million, 

 and it is possible that even this figure might have been exceeded 

 without introducing any great error, though no attempt was 

 made to find the exact limiting concentration possible. Twenty- 

 five parts per million may be regarded as a safe maximum. 

 Even with very high initial concentration, aspiration of five 

 to ten minutes was sufficient to bring the quantity of free 

 carbon dioxide below this limit. 



2. Removal of carbon dioxide. — Boiling the solution for from 

 five to ten minutes to remove carbon dioxide, as advised by 

 several investigators, before titrating with potassium palmitate, 

 was found to have no more beneficial effect than aspiration for 

 five minutes. 



3. Effect of salt. — Sodium chloride in the amounts normally 

 found in natural waters has no effect on the results. Concen- 

 trations varying from 10 to 2,000 parts per million of chlorine 

 were employed, without perceptibly affecting the end point. 



4. Dilution of very hard water. — If the total hardness (as 



' Received for publication October 2, 1916. 



''Blacher C, Grunberg, P., and Kissa, M., Chem. Zeitg. (1913), 37, 56-8. 



291 



