Today Sara and I set up a darkroom at Northeastern University. We prepared fixer in order to make a batch of hydrogen sulfide sensing strips using photographic paper. Fixer is diluted in a 1:10 ratio with water. Fill graduated measuring cup to bottom line with fixer, fill cup to second line with water. To check viability of fixer, add a few drops of hypo-chek. If solution is cloudy, fixer is no longer usable. Fixer is hazardous waste and must be labeled as such and disposed of in the waste container.