From the wikipedia page:
4th analytical group of cations
The fourth group of cations include Zn2+, Ni2+, Co2+, and Mn2+. This group is determined by the addition of ammonium chloride, ammonium hydroxide, and hydrogen sulfide gas to the solution of the salt. A colored precipitate indicates Mn2+...
Is is really neccessary to add hydrogen sulfide gas or I can add it as a liquid, because I don't know how to add it as a gas, or is there any better way to determine Mn2+ ions?