Gasometric Determination of Oxalic Acid and Calcium, and Its Application to Serum Analysis.* by Donald

is the basis of most of the calcium methods current in biological chemistry, the amount of oxalate in precipitated calcium oxalate being determined by titrimetric measurement of the permanganate utilized. In this paper we present results showing that the oxalate can be determined with equal accuracy by measurement in the Van Slyke-Neil1 (1924) manometric apparatus, and that the gasometric procedure can be applied with especial advantage to micro determination of serum calcium. The advantage of the gasometric method in micro analyses is indicated by the fact that the oxalate precipitated by 0.1 mg. of Ca, the amount in 1 cc. of ordinary serum, reduces in titration only 0.50 cc. of the 0.01 N permanganate used in the Kramer and Tisdall (1921) method, while by the gasometric procedure the COZ produced exerts at 0.5 cc. a pressure of about 160 mm. to read on the Van Slyke-Neil1 manometer. The permanganate without unusual precautions can hardly be measured with better than 4 per cent accuracy, while 1 per cent is easily attainable in the manometric measurement. With larger amounts of oxalate to determine, titration and gasometric measurement yield precise and identical results.