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.
104/526 page 80
![[§§ 82, 83. converting it to a state which permits of its subsequent reduction by hydrogen. Carbonate of soda also is the most sensitive reagent in the dry way for the detection of manganese, as, when fused in the outer flame with a substance containing manganese, it yields a green opaque bead, owing to the formation of manganate of soda. § 82. 2. Cyanide of Potassium, HaN = KCy [KCNj. Preparation.—See § 54. Uses,—Cyanide of potassium is an exceedingly powerful reducing agent in the dry way ; indeed it excels in its action almost all other reagents of the same class, and separates the metals not only from most oxygen compounds, but also from many sulphur compounds. This reduction is attended in the former case with formation of cyanate of potassa, by the absorption of oxygen, and in the latter case with forma- tion of the sulphocyanate, by the taking up of sulphur. By means of this reagent, we may effect the reduction of metals from their com- pounds with the greatest possible facility; for instance, we may obtain metallic antimony from antimonious acid or from sulphide of antimony, metallic iron from sesquioxide of iron, &c. The readiness with which cyanide of potassium enters into fusion facilitates the reduc- tion of the metals greatly; the process may usually be conducted even in a porcelain crucible over a spirit or gas-lamp. Cyanide of potassium is a most valuable and important agent for reducing bin oxide of tin, antimonic acid, and more particularly tersulphide of arsenic. Cyanide of potassium is equally important as a blowpipe reagent. Its action is exceedingly energetic; substances like binoxide of tin, the reduction of which by means of carbonate of soda requires a tolerably strong flame, are reduced by cyanide of potassium with the greatest facility. In blowpipe experiments, we invariably use a mixture of equal parts of carbonate of soda and cyanide of potassium; the admixture of carbonate of soda is intended here to check in some measure the excessive fusibihty of the cyanide of potassium. This mixture of cyanide of potassium with carbonate of soda, besides being a far more powerful reducing agent than the simple carbonate of soda, has moreover this cfreat advantage over the latter, that it is absorbed by the pores of the charcoal with extreme facihty, and thus permits the production of the metallic globules in a state of the greatest purity. § 83. 3. Biborate of Soda or Borax, NaO,2BO, [Na.,B,o.]. Crystallized, NaO,2B03lOaq [Na,BA.10Hp]. The purity of commercial borax may be tested by adding to its solu- tion carbonate of soda, or, after previous addition of nitric acid, solution of nibrate of baryta or of nitrate of silver. The borax may be con- sidered pure if these reagents do not produce any alteration m the solution; but if either of them causes the formation of a precipitate, or renders the liquid turbid, recrystallization is necessary. The pure crys-](https://iiif.wellcomecollection.org/image/b21966953_0104.jp2/full/800%2C/0/default.jpg)
