292 The Philippine Journal of Science i9i6 



calcium carbonate) is much over 250 parts per million, it may- 

 be found convenient to dilute a water sample with distilled 

 water to prevent the heavy precipitate from obscuring the end 

 point. A 100 cubic centimeter sample may be diluted to at 

 least 500 cubic centimeters with distilled water, without ap- 

 preciably affecting the end point. 



5. Distinction of end points. — An effort was made to distin- 

 guish the three end points mentioned by Herbig,=' namely, a 

 very faint red, followed by a light red, followed by an intense 

 red, the last of which, Herbig states, is the one to be used 

 in almost all cases, particularly in waters high in magnesium. 

 With solutions containing only calcium, the first two end points 

 lie very close together, so that either could be taken as the true 

 end point and give results well within the limits of experimental 

 error. With solutions containing considerable amounts of mag- 

 nesium, the first end point was reached long before a value 

 corresponding to the true end point was obtained. Additions 

 of potassium palmitate after the second end point had been 

 reached produced deepening of the phenolphthalein coloration, 

 apparently corresponding simply to successive transformations 

 of additional amounts of indicator. No sharp transition point 

 was observed, so that the third end point mentioned by Herbig 

 could not be located. 



By taking the second end point, mentioned in the preceding 

 paragraph, very satisfactory results were obtained, whether the 

 hardness of water was caused by calcium or by magnesium, 

 singly or combined. Determinations made in a considerable 

 number of both artificially prepared and natural waters, checked 

 by gravimetric determinations, showed an average variation of 

 2 to 3 per cent from the true calcium and magnesium content — 

 a degree of accuracy comparable with that obtained by J. Zink 

 and F. Hollandt,* and by E. Nochmann.^ 



Using these data as the basis of any deviation from Blacher's 

 original procedure, the method as finally adopted is as follows : 



A 0.1 N potassium palmitate solution is prepared, according to 

 the method given by Herbig " for potassium stearate, by the 

 neutralization of palmitic acid in alcoholic glycerol solution. 

 This solution is standardized against a saturated solution of 

 calcium hydroxide." 



''Herbig', W., Farber Zeitg. (1913), 24, 98-101. 

 ' Zeitschr. f. angew. Chem. (1914), 27, 1, 439. 

 '" Pharon. Zentralh. (1914), 55, 436-7. 

 <" Farber Zeitg. (1913), 24, 113-4. 

 ' Blacher et al, loc. cit. 



