The article by Earl Judson King discusses the colorimetric determination of phosphorus, focusing on the advantages of using perchloric acid over sulfuric acid in the process. The method combines the improvements from the work of Martland and Robison, who modified the Briggs procedure by allowing the color to develop at a higher acidity, and Fiske and Subbarow, who suggested using 1:2:4-aminonaphtholsulphonic acid as a reducing agent for faster and more consistent color development. Perchloric acid is highlighted for its superior oxidation properties, ease of use, and minimal interference from various substances. The procedure involves measuring the sample in a boiling tube with perchloric acid, followed by the addition of molybdate and aminonaphtholsulphonic acid, and reading the color after 5 minutes. The method is particularly useful for determining total phosphorus in samples where organic matter needs to be destroyed, such as in blood and urine. The article also includes tables showing the results of analyses using this method, demonstrating its effectiveness and reliability.The article by Earl Judson King discusses the colorimetric determination of phosphorus, focusing on the advantages of using perchloric acid over sulfuric acid in the process. The method combines the improvements from the work of Martland and Robison, who modified the Briggs procedure by allowing the color to develop at a higher acidity, and Fiske and Subbarow, who suggested using 1:2:4-aminonaphtholsulphonic acid as a reducing agent for faster and more consistent color development. Perchloric acid is highlighted for its superior oxidation properties, ease of use, and minimal interference from various substances. The procedure involves measuring the sample in a boiling tube with perchloric acid, followed by the addition of molybdate and aminonaphtholsulphonic acid, and reading the color after 5 minutes. The method is particularly useful for determining total phosphorus in samples where organic matter needs to be destroyed, such as in blood and urine. The article also includes tables showing the results of analyses using this method, demonstrating its effectiveness and reliability.