The Determination of the Buffer Alkali in Cutaneous Blood*

Greenwald and Lewman (1) described a method in which the protein and carbonic acid of blood are removed by picric acid, so that the alkali of the proteinates and bicarbonate is replaced by an equivalent of alkali picrate, which is measured. The picric acid precipitates the protein and frees the COZ, which is boiled off from the filtrate. The alkali picrate is measured as total picric acid minus free picric acid, and represents the buffer alkali of the proteinates and bicarbonate, called “titratable alkali” by Greenwald and Lewman. As will be shown later, the “buffer alkali” measured by the picrate method includes nearly the total buffer alkali of plasma, but only about 80 per cent of that in the whole blood, the remainder being chiefly in the form of alkali salts of organic phosphates in the cells. The picric acid method nevertheless gives a useful measure of the alkali in the more important buffers of the blood. Greenwald and Lewman titrated the excess picric acid with 0.01 or 0.005 N NaOH to end-points with several indicators-methyl red, phenol red, and thymolphthalein. The total picrate was estimated either gravimetrically as nitron picrate or by titration with titanous chloride. Sumner and Hubbard (2) subsequently used dinitrosalicylic in place of picric acid, since the former can be determined calorimetrically. The use of dinitrosalicylic acid has the disadvantage, however, that the titration of the acid to a