CI Sulfite Test Kit is a drop-count field test kit for measuring sulfite residual as SO₃ in industrial water systems where sulfite is used to control dissolved oxygen and limit oxygen-driven corrosion. Used on a 25 mL water sample, the test runs by drop-count titration to endpoint, with each drop equal to 6 ppm sulfite, giving the operator a direct check on whether residual is actually sitting inside the intended treatment range. That matters because sulfite only protects the system when enough residual is being maintained to keep oxygen scavenging active; if the residual falls too low, corrosion protection drops away, and if it runs too high, the program may simply be overfeeding chemistry without benefit. Compact, straightforward, and built for routine monitoring, this kit is the operator-side complement to sulfite-based treatment programs: the chemistry removes oxygen, and the test kit confirms the residual is really there.