Method and apparatus for detecting and measuring a gas

Claim 1

In a method for measuring the amount of hydrogen cyanide in a gas stream by utilizing a hydrogen cyanide absorbing reagent liquid, which upon exposure to and absorption of hydrogen cyanide, undergoes a color change upon passage of the exposed reagent liquid through a heater for subsequent analysis of the reagent liquid in a color detector, the improvement comprising the steps of: passing the stream of gas in counter flow relationship with a flow of hydrogen cyanide absorbing reagent liquid for exposure to and absorption by the latter of hydrogen cyanide while feeding the reagent liquid under gravity in a well defined stream; controlling the flow rate of said exposed reagent liquid at a point subsequent to its exposure to hydrogen cyanide and prior to the entry of the reagent to the heater with a predetermined head of the reagent liquid above said heater by optically sensing the reagent liquid at a predetermined level above said heater; and varying the flow of said reagent liquid at a place above said heater to maintain a meniscus of the reagent liquid at said predetermined level thereby establishing through said heater a substantially constant flow rate for a consistent measurement of the color of said exposed reagent liquid.