Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![NITRATE OF SILVEE. of oxygen from it; the decomposition of the nitric acid being attended in this case with the foi-mation of a very deep brownish-black com- pound of nitric oxide with a portion of the undecomposed salt of the protoxide of iron : this reaction afFoi-ds a particularly characteristic and delicate test for the detection of nitric acid. Ferrous sulphate is also used to detect hydroferricyanic acid, with which it produces a kind of Prussian blue, and also to precipitate metallic gold from solutions of the salts of that metal. § 65. 2. Ferric Chloride or Sequichloride of Iron, Fe,Cl3 [Fe,CI„]. Preparation.—A mixture of 10 parts of water and 1 part of pure hydrochloric acid is heated in a flask with small iron nails until no further evolution of hydrogen is observed, even after adding the nails in excess; the solution is filtered into another flask, and chlorine gas passed into it with frequent shaking, until the solution no longer produces a blue precipitate with ferricyanide of potassium; it is then heated until the excess of chlorine is expelled. The solution is diluted until it is twenty times the weight of the iron dissolved, and kept for use. Tests.—Solution of ferric chloride should not contain an excess of acid ; this may be readily ascertained by stirring a diluted sample of it with a glass rod dipped in ammonia, when the absence of any excess of acid will be proved by the formation of a precipitate which shaking the vessel or agitating the liquid fails to redissolve. Feri-icyanide of jjotas- sium should not impart a blue colour to it. Uses.—Ferric chloride is used for subdividing the group of organic acids which chloride of calcium fails to precipitate, as it produces pre- cipitates in solutions of benzoates and succinates, but not in cold solu- tions of acetates and formates. The aqueous solutions of the neutral acetate and formate of sesquioxide of iron exhibit an intense red colour; ferric chloride is therefore a useful agent for detecting acetic acid and formic acid. Ferric chloride is exceedingly useful for effecting the decom- position of phosphates of the alkaline earths (see § 142, 9); and it serves also for the detection of hydroferrocyanic acid, with which it jjroduces Prussian blue. § 66. 3. Nitrate of Silver, AgO,NO, [AgNO,]. Preparation.—1 part of the pure commercial salt is dissolved in 20 parts of water. Tests.—Dilute hydrochloric acid should completely precipitate all the fixed matter from solution of nitrate of silver; the filtrate from the precipitated chloride of silver therefore must leave no residue when evaporated on a watch-glass, and should be neither precipitated nor coloured by sulphuretted hydrogen. Solution of nitrate of silver should have a neutral reaction. Uses.—Oxide of silver forms soluble compounds with some acids, and with others insoluble compounds. Nitrate of silver, therefore, like](https://iiif.wellcomecollection.org/image/b21966953_0094.jp2/full/800%2C/0/default.jpg)
