Lead Acetate Test Paper by Precision Laboratories.
This Lead Acetate Test Paper detects Hydrogen Sulfide in water in concentrations as low as 5ppm. Use this test paper to test your drinking water, well water or groundwater.

Instructions:
Dip the test paper into the water for a few seconds, and remove.
At approximately 1-3ppm, the white paper will start to turn grey.
As the concentration increases, the color of the paper will turn darker up to 400ppm.
You can also moisten the paper with distilled water and place in an area where Hydrogen Sulfide is thought to be present (an acetate buffer is not necessary).
Note: Lead Acetate test paper does not cross-react with thiols, thioketones or mercaptans: these produce a negative response.