STUDIES ON AMYLASES: IV. A FURTHER INVESTIGATION OF THE PROPERTIES OF PANCREATIC AMYLASE.2
Journal of the American Chemical Society
acid is precipitated with calcium acetate after acidifying with acetic acid, and the precipitate is titrated with standard hydrochloric acid. Or the method frequently used was to acidify the filtrate strongly with sulfuric acid and titrate with potassium permanganate. The potassium permanganate used is calculated to oxalic acid. Dr. Denis states that the above work' was confirmed repeatedly. She also made titrations of lactic 'acid by adding 0. I N potassium permanganate to the alkalin
... he alkalin solution. When no more potassium permanganate was reduced the solution was strongly acidified and the manganese dioxide reduced with 0.2 N oxalic acid. These experiments showed that 4.84 and 4.87 atoms of oxygen were consumed instead of 5 atoms per molecule, as demanded by the equation. The average difference of 3.4% was no doubt attributed to error. In experiment (f> above on zinc lactate the products accounted for 5.05 atoms of oxygen per molecule of lactic acid. The amount of potassium permanganate used was equivalent to 5.13 atoms of oxygen or 2.6y0 in excess, In experiment (e) the conditions used were much the same as those used by Ulzer and Seidel and the amount of acetic acid formed was larger. Our own experiments have shown that the reaction is not as simple as was assumed by the former workers. The analytical error in working by Ulzer and Seidel's method may vary a great deal, depending on the temperature, the dilution, the concentration of the alkali, etc. The error in Denis' adaptation of it would never be so large because the potassium permanganate used in the oxidation is the basis of calculation. This is an excess of I%.