The measurement results are readily visible. When the sample gas is vented into the detection tube, the chemical reacts with the gas and discoloration. Detection tube for the Kitagawa type vacuum gas harvester AP-20. Target gases: Water quality detection tube (chlorine ion); Measurement range (ppm): 3 - 200; Effective period (years): 2; Country of Origin: Japan; Weight: 3.5 oz (100 g)