disadvantage. Impregnated tape methods also sacrifice some precision by comparison with the Methylene Blue procedure but this is minimal and is more than offset by superior specificity, portability, lower cost, and greater ease of operation in the automatic mode. It is apparent that many of the criticisms of impregnated tape methods can be attributed to insufficient recognition of the precautions necessary for good quantitative analyses. These are summarized below for determination of 0.1 ppm H2S: AgNO3-Flow rate 40 "C, avoid high flow rates at very low humidities (
