For the determination of phosphoric acid in brewing water, three methods with naked eyes used up to the present were examined in detail for their standard curves by using a photoelectric colorimeter.
The three standard curves were very nearly straight lines on semi-logarithmic graph and so adapted for the Lambert-Beer's law.
The method A (themodified Brigg's method) was best among the three methods, by the reason of suitability of the standard curve for the determination and the variation of color from the time of adding reagents.
Still more we attempted experimentation repeatedly, and recognized that the color depth was- Stable 60 min. after adding reagents.
Comparison of the method A and the method with naked eyes showed that the former was quicker, easier, and more accurate than the latter.
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