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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![And, as is tlie case with the bcaryta precipitates, the different conditions under which the various insohible lime salts are thrown down enables us to subdivide the group of precipitable acids. § 63. 6. Sulphate of Magnesia, MgO,SO, [MgSOj. Crystallized, MgO,S03 + 7aq [MgS0„7H,0]. Fre2)aration.—1 part of commercial sulphate of magnesia is dissolved in 10 parts of water; if the salt is not perfectly pure, it should be recrystallized. Tests.—Sulphate of magnesia should have a neutral reaction. Its solution, mixed with a sufficient quantity of chloride of ammonium, should not appear clouded or tinged by pure ammonia, or by carbonate or oxalate of ammonia, or by sulphide of ammonium, even after the lapse of half an hour. l/ses.—Sulphate of magnesia is used almost exclusively for the detection of phosphoric acid and arsenic acid, which it precipitates from aqueous solutions of phosphates and arsenates, in presence of ammonia and chloride of ammonium, in the form of almost absolutely insoluble, highly characteristic double salts (basic phosphate or basic arsenate of magnesia and ammonia). Sulphate of magnesia is also employed to test sulphide of ammonium (see § 40). c. Salts of the Oxides of the Heavy Metals. § 64. 1. Perrons Sulphate or Sulphate of Protoxide of Iron, reO,S03 [FeSOJ. Crystallized, FeO,S03 + 7aq [FeS0„7H,0]. Fre2Kirat{o7i.—Iron in the form of nails free from rust, or clean iron wire, is heated with dilute sulphuric acid until the evolution of hydrogen ceases, taking care to keep the iron in excess; the solution is concen- trated, filtered, a few drops of dilute sulphuric acid added to the filtrate, and it is then allowed to cool. The crystals which are deposited are washed with water very slightly acidified with sulphuric acid, dried and kept for use. Fei-rous sulphate may also be prepared from the solution obtained when sulphide of iron is dissolved in dilute sulphuric acid, as in the process of evolving sulphuretted hydrogen. I'ests.—The crystals of ferrous sulphate should be of a fine pale-green colour. Crystals that have been more or less oxidized by the action of the air, and give a brownish-yellow solution when treated with water, leaving basic ferric sulphate undissolved, must be rejected. Sulphu- retted hydrogen should not precipitate solution of ferrous sulphate after it has been acidified with hydrochloiic acid, or even impart a blackish tint to it. Uses.—Ferrous sulphate has a great tendency to absorb oxygen, and to be converted into the ferric sulphate ; it acts therefore as a powerful reducing agent. It is employed principally for the reduction of nitric acid, from which it separates nitric oxide by withdrawing three atoms](https://iiif.wellcomecollection.org/image/b21966953_0093.jp2/full/800%2C/0/default.jpg)
