In following the various procedure of Qualitative Analysis the purpose of the operator is to separate, as completely as possible, the substances present and to identify each in its proper order. Experience has shown the value of working with solutions, whenever the substance to be examined can be dissolved, either in whole or in part, by the ordinary solvents. If more than one compound is present in aqueous solution, however, it very frequently becomes impossible for the analyst to do more than determine the various ions. Since ions are best removed from solution by adding other ions with which they will form relatively difficulty soluble compounds, the analyst adds to the solution, in a definite order, those reagents containing the ions which he chooses, having arbitrarily added a certain kind of ion, under given conditions, the production of precipitate indicates that certain ions were in the solution. He then examines the precipitate to determine which of the possible ions are present.