The organic substances are first destroyed by means of chlorate of potassa and hydrochloric acid. When this is accomplished, the excess of chlorine is removed by boiling and the liquid filtered. The portion remaining on the filter is preserved: it contains all the silver and a large portion of the lead, if these metals are present. We will designate the residue as A, the filtrate as B. TREATMENT OF RESIDUE A. The residue is calcined with a little carbonate of soda and cuttings of pure Swedish filtering paper, the chlorides present being reduced to the metallic state by this treatment. The residue is next taken up with water acidulated with nitric acid, and the solution filtered. An insoluble residue, that may remain, is washed with hot water until the wash-water ceases to precipitate solution of nitrate of silver, and dried. It is then dissolved in boiling nitric acid, the solution diluted with water, and filtered.[K] [K] If an insoluble residue remains by the treatment with nitric acid, it may consist of _tin_. In this case, it is dissolved in _aqua regia_, the metal precipitated by immersing a plate of zinc in the solution and then re-dissolved in boiling hydrochloric acid. Upon adding chloride of gold to the solution so obtained, a purple precipitate is formed. Sulphuretted hydrogen produces a brown precipitate, soluble in sulphide of ammonium, in presence of tin. Sulphuric acid is added to the filtrate: if no precipitate forms, the absence of _lead_, in the residue A, is indicated. If, on the contrary, a precipitate is produced, it is collected upon a filter and washed. In order to make sure that the precipitate consists of sulphate of lead, it is treated with a solution of tartrate of ammonia: it should dissolve, forming a solution in which sulphuretted hydrogen produces a black precipitate. The fluid which has failed to be precipitated by the addition of sulphuric acid, or the filtrate separated from the precipitate formed, can contain only silver. Upon adding hydrochloric acid, this metal is thrown down as a caseous white precipitate, which is soluble in ammonia, but insoluble in boiling nitric acid, and blackens upon protracted exposure to light. The formation of a precipitate possessing these properties, leaves no doubt as to the presence of _silver_.