Copy 1, Volume 1

Hand-book of chemistry / Translated by Henry Watts.

  • Gmelin, Leopold, 1788-1853
Date:
1848-1872
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of chemistry / Translated by Henry Watts. Source: Wellcome Collection.

    489/562 (page 465)
    wire under these circumstances quickly and repeatedly becomes red, blue, yellow, red, blue, yellow, &c. The colour, however, becomes deeper every time, and at last so deep that the different tints cannot be distinguished. (Schénbein.) | To form a Nobili’s monochromatic deposit on platinum, the following solutions may be used; Chloride of manganese in 8 parts of water, sulphate of manganese and potash in 12, acetate of manganese in 15, succinate of manganese in 16, or hippurate of manganese in 12 parts of water. A well-polished platinum capsule is filled with one of these solutions, and connected with the positive pole of a battery of 4 pairs of plates (each plate 36 square inches in surface), immersed in dilute sulphuric acid (if a stronger battery is used the solution of the salt must be more dilute); a disk of platinum 3 of an inch in diameter is then dipped horizontally into the liquid to form the cathode. With sulphate of manganese and potash, or with succinate or acetate of manganese, one uniform tint is invariably produced, first golden yellow, then purple, then green; the current must therefore be stopped as soon as the desired tint is completely developed. With hippurate of manganese the capsule is first tinted golden yellow, then of a splendid bluish purple red. Chloride of manganese yields very beautiful broad alternating rings of purple green, golden yellow, and blue, surrounded by a broad belt of golden yellow. (R. Bottger, Pogg. 50, 45.) Nobili’s rings may also be formed by a simple galvanic circuit. When a plate of silver immersed in a solution of sulphate of copper is touched with the pointed extremity of a piece of zinc, there are formed round the point of contact a number of blue and green rings, which, when the zine is removed, run through several changes of colour, finally becoming dark blue and lightish green.—In the colourless copper solution formed by leaving copper filings in contact with a saturated solution of sal-ammoniac in a closed vessel containing air,—silver or platinum becomes covered with copper, if it be touched below the surface of the liquid with a pointed piece of zinc;—but when the zine is removed, the coating of copper gradually disappears, the action commencing from the outside (where the coating is thinnest) and proceeding towards the middle. (Fechner, Schw. 55, 442.) If however the platinum thus covered with copper be immedi- ately dipped into water, so as to remove the ammoniacal liquid by which it would be redissolved, the coppering remains permanent ; and if the zine be left for a longer time, about two minutes, in contact with the platinum in the ammoniacal solution of copper, until it evolves gas and precipitates copper of a black colour, the platinum loses its thin coating of copper and becomes tinted with various shades of yellow, green, red, and especially black, which latter colour it then retains after drying. (R. Bottger, J. pr. Chem. 8, 476.) (For the decomposition of organic compounds by the electric current, vid. Oxalic acid, Tartaric acid, Acetic acid, Wood-spirit, Alcohol, Ether, and the Organic Bases.) Decomposition of several Liquids in Contact with one another. When the electric current has to traverse a number of liquids [or to effect a transportation of atoms in them] which are either in immediate contact or separated from one another by a porous body, it at first deposits VOL. I. 2H