The following are simple tests for impurities in water. Add Nessler's reagent; if ammonia is present, the water will in a few moments become distinctly yellow. Add to another portion dilute sulphuric acid, and warm; while hot, add drop by drop a very dilute solution of permanganate of potash (strength I parts in 10,000); should the pink colour disappear even after several drops have been added, there is probably much organic mutter present; if the colour of one or two drops is not discharged, the water is pretty free from this pollution. Nitrites are tested for by a few drops of sulphuric acid and a solution of metaphenylene diamine, which will yield a bright yellow colour. Nitrites usually show pollution when present, but often they are not present in bad waters: they are not important unless present in very large quant [ties.