The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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it is desirable to cut the lantern glasses and the glasses of the coloured spectacles from the same sheet.
Analysisin the sense of thorough, anda re-
lease). In common language, the term analysis is often applied to a mere testing whereby evidence of the presence of a substance is obtained, although no attempt is made at the separation of the substance, and the use of litmus paper in testing for acids and alkalies (see Acidity) would often be spoken of as a rudimentary operation in analysis. When the object of analysis is merely to separate sufficient of a substance for recognition, the operation is called qualitative analysis, while the operation is called quantitative when the amount of a constituent is determined. A person without thorough chemical training is very liable to be misled by any attempt at systematic analysis or testing; but in spite of this we give a very concise abstract of a modification of the usual routine of systematic testing for the common metals, as applied to substances soluble in water or in acids : About 20 grs. of the substance in two drams of water - either with or without the aid of an acid - forms the original solution, O.S. Add to O.S. hydrochloric acid drop by drop ; a white precipitate in-soluble in excess indicates lead, silver, or mercurous compounds. Let the precipitate settle, pour off liquid, add water; shake ; allow precipitate to settle, and pour off; then add ammonia. The dissolving of the precipitate indicates silver ; if unchanged, lead; if blackened, mercury. If hydrochloric acid gives no pre-cipitate add excess of sulphuretted hydrogen solution to the same solution. A black precipitate indicates mercury (mercuric), copper, or lead (if proportion in original was small). To O.S. add ammonia ; a cobalt blue coloration, preceded maybe by a greenish precipitate, indicates copper; mercury is indicated by boiling original substance with water and a drop or two of nitric acid, a bright copper wire being immersed, when the copper will be coated with mercury; if lead, the original solution will give a white precipitate with sulphuric acid, this precipitate being insoluble in nitric acid. To original solution add ammonia; ferrous salts give a dark precipitate, becoming rust-coloured on exposure to air; ferric salts give the rust-coloured precipitate at once ; aluminium salts give a transparent white precipitate under these circumstances ; chromium, a greenish precipitate. If no