The combination of proteins, amino-acids, etc., with acids and alkalis, and their combining weights as determined by physico-chemical measurements.—Preliminary paper

Abstract
In previous communications (1) the writer described a system for estimating and characterising the amino-acids which depends on thekaandkbvalues of these bodies. Themodus operandiof the technique is to determine the amounts of acid or alkali required to titrate the amino-acid- (or dipeptide-, etc.) solutions over definite ranges ofpHor to definitepHend-points; it rests on the knowledge that the weaker an acidic (or a basic) group the greater will be the degree of alkalinity (or acidity) developed during its titration with strong alkali (or acid). After the addition of each increment of acid or alkali thepHis determined. One plotspHagainst,notthe actual amount of alkali (or acid) added, but against this amount corrected for the “hydrogen ion error.” The correction is made by subtracting from the amount of alkali (or acid) added, the amount of alkali (or acid) which would have to be added to a hypothetical blank consisting of water only in order to produce the same total volume of liquid having the samepHas the amino-acid alkali (or acid) mixture. The corrected value represents the amount of alkali (or acid) required to bring the amino-acid itself to the givenpHvalue, while the correction is the amount required by the water present.

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