Abstract: Apparatus for quantitative analytical measurements using capillarity-based analytical devices is described. Porous cellulose (i.e., common filter paper) may be used as the reagent carrier for the analyses. Hydrophobic materials may be printed onto the paper to generate paths that restrict liquid flow by capillary action to defined regions. At least one colorimetric reagents effective for reacting with a specific analyte is deposited along a capillary flow path generated in the device. Upon placing the liquid containing the analyte on one end of the path, the liquid moves along the circuit by capillary action, and the flowing analyte reacts with reagent generating color along the flow path until all of the analyte is consumed. Analyte quantification is achieved by measuring the length of the colored portion along a flow path employing a direct-reading measurement scale.