# Indicator for H2S [closed]

In there an indicator for sulfur compounds like H2S (also organic)?

Or some straight forward way to measure if the H2S concentration in the air is higher than usual? Or is the concentration too low anyway?

• Your nose is an excellent and extremely sensitive detector. ;)
– Karl
Jan 18 '20 at 14:21
• (do not overtax it however. 200ppm of hydrogen sulfide are quite toxic, and your nose is already in overload then, you hardly smell it any more.) The lower human detection limit is somewhere around .5 ppb according to wikipedia.
– Karl
Jan 18 '20 at 15:52

Oil production areas use a personal badge; lead acetate , it darkens if H2S is present ( Draeger was a brand for detection equipment).

• To OP: this was and probably still is the standard H2S indicator also in analitical labs, and in school and university labs. Jan 19 '20 at 7:33
• @Alchimista I think the use of H2S bottles in school or undergrad labs has cheased in the meantime (TAA was standard at my university twenty years ago already), and if you wanted one for your research, I´m sure your lab safety people will equip you with a modern electronic sensor that beeps. ;)
– Karl
Jan 28 '20 at 23:10
• @Karl TAA was in use already at my times. Still, lead acetate paper was part of the kit for every one. I guess that for safety the electronic device should be the choice because of its alerting beep. If a lab might have dozens of them to be used atop dozens of beckers almost simultaneously I don't know. pHmetres don't replace litmus paper, at the end. Ps: H2S bottles probably means Kipp's apparatuses. Jan 29 '20 at 8:28
• @Alchimista I never worked with gaseous H2S, but yea, according to my old firstyear textbook, it would have come from a Kipp, not a bottle. ;) It also mentions lead acetate paper, but I guess our profs thought that the chances of anyone who couldn´t smell H2S any more noticing the blackening of a piece of paper were just too small to be worth caring about.
– Karl
Jan 29 '20 at 18:20
• @Karl I just have said that lead acetate paper is the common indicator for sulphides and sulphydric acid. I hope that the Lassaigne test is still performed, and with a stripe not an electronic detector :) Jan 30 '20 at 7:44

On the premises of an oil refinery, if you are not staying completely indoors, everybody gets one of these:

They give you an alarm if the H2S concentration goes above a few ppms, and the sensor inside typically can (quantitatively) measure up to one or two hundred ppm before it goes into saturation.

There are simple test tubes available for the measurement of $$\ce{H2S}$$ and similar compounds in air. For example this one by Dräger (no affiliation), which uses oxidation by iodine. $$\ce{H2S + I2 -> 2 HI + S}$$ The (discoloration of the) brown color of the absorbed iodine serves as indicator.

In order to get a quantitative result for the concentration in air, you would need to pump a defined volume of air through the test tube.

• "Standard Measuring Range: 0.2 to 7 vol. %" The lower end of that range is lethal to humans within minutes.
– Karl
Jan 18 '20 at 14:25