Abstract: A hydrogen sulfide analyzer that continuously samples waste water from a waste stream or reservoir and measures the concentration of purgeable H.sub.2 S present (H.sub.2 SP) This information, when combined with the volume of water present, provides a control quality signal that regulates the feed rate of the destructor chemical into the waste stream. This results in chemical savings for the user. A second result is the reduction in odor complaints and the corrosion problems associated with H.sub.2 S emissions. The analyzer measures only the purgeable H.sub.2 S contained in the liquid sample. The analyzer violently agitates the sample containing dissolved H.sub.2 S in solution to simulate actual conditions at points of agitation in the waste water stream. It also provides nearly optimal partial pressure conditions for the H.sub.2 S to exit the solution as a free gas. Any H.sub.

Abstract: To measure flow rates, the cross-sectional shape of the flow path is changed by inserting a multiple position gate into the flow path and altering the position of the gate to maintain the head of liquid constant with a reduced flow cross section. To maintain the head at a desirable range, the depth is measured and controls the position of the gate as a feedback signal. The position of the multiple position gate is correlated with the depth to provide an indication of flow rate. For this purpose, a flow path housing is clamped to a pipe and a multiple position gate is moved by pneumatic pressure into the flow stream to change the flow cross section. The depth of the head upstream of the gate is measured and the position of the gate is measured. Flow rate is determined from these two measurements. Sampling may be performed at an increased depth caused by the gate.