(1). A current of sulphuretted hydrogen is conducted through the solution: the precipitation of some metals, usually thrown down by this gas, may fail to take place in this instance, owing to the presence of organic substances; however, some metals are precipitated, even in presence of organic compounds, and organic acids are but seldom present. In case a precipitate is formed, it is mixed with pure silica, collected on a filter, and treated with nitric acid. If the precipitate fails to dissolve, it is treated with _aqua regia_. In either case, the solution obtained is examined for metals by the ordinary methods. (2). The solution in which sulphuretted hydrogen failed to produce a precipitate, or the filtrate separated from the precipitate formed, is divided into two parts: one portion is treated with ether and a solution of potassa; the other with ether and a solution of soda. Both mixtures are then well agitated, and notice taken if the ether dissolves any thing: if so, the operation is repeated several times until all soluble substances are removed. The ethereal solutions are next decanted and united, and then submitted to the examination for alkaloids as directed pp. 65-84. (3). If--the above treatment giving either positive or negative results--a precipitate insoluble in ether is formed by the addition of potassa or soda, it is collected on a filter, washed, and dissolved in an acid. The solution is then tested for mineral bases. (4). In case no definite result has been obtained by the preceding operations, one of the portions (for instance, the one to which potassa was added) is tested for the acids possibly present in the state of salts. The solution is divided into two parts (A and B) which are examined separately: PORTION A.--This is evaporated to dryness and the residue divided into four parts which are then tested for hydrofluoric, nitric, oxalic, and acetic and formic acids. _a._ HYDROFLUORIC ACID.--A portion of the residue is heated in a platinum crucible with sulphuric acid, and the crucible covered with the convex face of a watch-crystal coated with wax in which lines have been traced with a pointed piece of wood. If, after gently heating the crucible for some time and removing the watch-crystal, the lines traced in the wax are found to be etched in the glass, the substance under examination contains a _fluoride_. _b._ NITRIC ACID.--If this acid be present, and a second portion of the residue is heated with sulphuric acid and copper, reddish-fumes are evolved. Upon conducting the vapors into a solution of sulphate of iron or narcotine, the reactions already mentioned in treating of nitric acid take place.