Ferrocyanide Sentence Examples
He mentioned as an important exception the case of ferric ferrocyanide, which, when dissolved in oxalic acid, transmits the rays in great abundance, though the same rays be absorbed both by ferrocyanides and by ferric salts.
The most modern and the most generally accepted method is volumetric, and is based on the reaction between zinc chloride and potassium ferrocyanide, by which insoluble zinc ferrocyanide and soluble potassium chloride are formed; the presence of the slightest excess of potassium ferrocyanide is shown by a brownish tint being imparted by the solution to a drop of uranium nitrate.
They are soluble in water and give characteristic precipitates with platinic and auric chlorides, and with potassium ferrocyanide.
It may also be prepared by heating formic and oxalic acids (or their salts) with concentrated sulphuric acid (in the case of oxalic acid, an equal volume of carbon dioxide is produced); and by heating potassium ferrocyanide with a large excess of concentrated sulphuric acid, K 4 Fe(CN) 6 -i-6H2S04+6H20=2K2S04+FeS04+3(NH4)2S04+6C0.
The soluble salts are removed by lixiviation, and the residue is boiled with lime to form the soluble calcium ferrocyanide, which is finally converted into the potassium salt by potassium chloride or carbonate.Advertisement
On the small scale it may be prepared by adding an acid solution of a ferrous salt to a solution of potassium ferrocyanide.
Potassium ferricyanide, K 3 Fe(NC)s, red prussiate of potash, is obtained by oxidizing potassium ferrocyanide with chlorine, bromine, &c., 2K 4 Fe(NC) 6 + C1 2 = 2K 3 Fe(NC) 6 + 2KC1.
It is prepared by oxidizing potassium ferrocyanide with a diluted nitric acid.
It may also be prepared by heating a mixture of carbon, oxide of iron and magnesite to bright redness; and by heating a mixture of magnesium ferrocyanide and sodium carbonate, the double cyanide formed being then decomposed by heating it with metallic zinc. Electrolytic methods have entirely superseded the older methods.
It was found, for instance, that a film of insoluble copper ferrocyanide, deposited in the walls of a porous vessel by the inward diffusion and meeting of solutions of copper sulphate and potassium ferrocyanide, would allow water to pass, but retained sugar dissolved in that liquid.Advertisement
Experiments with membranes of copper ferrocyanide have verified this result for solutions of cane-sugar of moderate dilutions.
Although even good membranes of copper ferrocyanide are rarely perfectly semi-permeable, and in other membranes such as indiarubber, &c., which have been used, the defects from the theoretical values of the equilibrium pressure are very great, yet, in the light of the exact verification of theory given by the experiments described above, it is evident that such failures to reach the limiting value in no wise invalidate the theory of osmotic equilibrium.
Potassium ferrocyanide gives a precipitate even in very dilute solution.
P. Pfeffer (Osmotische Untersuchungen, Leipzig, 1877) was the first to obtain satisfactory measurements of osmotic pressures of cane-sugar solutions up to nearly I atmosphere by means of semi-permeable membranes of copper ferrocyanide.
The ferrocyanide solution is standardized by dissolving i gramme of pure zinc in 6 cc. of hydrochloric acid, adding ammonium chloride, and titrating as before.Advertisement
Ferrous salts also give a bluish white precipitate with ferrocyanide, which on exposure turns to a dark blue; ferric salts are characterized by the intense purple coloration with a thiocyanate.
They give a characteristic pale red precipitate with sodium pyrophosphate, soluble in an excess of the precipitant; they also form precipitates on the addition of platinic chloride and potassium ferrocyanide.
It is now prepared from the calcium ferrocyanide formed in gas purifiers (see above) by decomposition with ferrous' sulphate.
Of the principal workers in this field we may notice Friedrich Hoffmann, Andreas Sigismund Marggraf (who detected iron by its reaction with potassium ferrocyanide, and potassium and sodium by their flame colorations), and especially Carl Scheele and Torbern Olof Bergman.
Ammonia gives a characteristic blue coloration when added to a solution of a copper salt; potassium ferrocyanide gives a brown precipitate, and, if the solution be very dilute, a brown colour is produced.Advertisement