Abstract
Since the “total acidity” of the urine has no chemical meaning it is often desirable to know the hydrogen ion concentration. At the suggeestion of Dr. J. B. Sumner, a sample of 4 nitro 6 aminoguaiacol which he kindly furnished, was used for this purpose. This appears to be a polybasic acid, which from pH 0 to 4 gives an increasing (yet always pale) yellow color, and from pH 4.5 to 8.5 gives an increasing henna color. The method is as follows:
In the left-hand cup of a Duboscq colorimeter place 0.5 cc. of an 0.1 per cent indicator, and 10 cc. of urine. In the right-hand cup place 0.5 cc. indicator, and 10 cc. 0.1 N NaOH solution. Adjust the left-hand cup to 20 mm., and hold under the right-hand cup a glass dish containing urine 20 mm deep. Determine the percentage dissociation (percentage color) in the left-hand cup. In highly acid urines a color match cannot be obtained in this way. It is then necessary to place over the eye piece a glass dish with some of the indicator in 0.01 N HC1. The following table gives the approximate pH at different percentage dissociation:
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