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.

    528/562 (page 504)
    reduction of copper on a plate previously ground and polished takes place with extreme slowness. Such a plate requires no grinding or polishing; and, in consequence of its homogeneity, the copper reduced. on its surface plates, the adhesion on some parts of the surface is so strong that the sary, before commencing the process of reduction, to cover the engraved plate with an extremely thin layer of grease. For example, it may be covered with melted stearic acid, which separates completely after cool- ing, but leaves a trace of grease (probably oleic acid), in a very finely divided state, on the plate of copper. The subsequent separation of the engraved plate before commencing the electro-type process. Gilding in the wet way is best adapted for the purpose. Pieces of copper stamped with the die may also be used as models, provided they are not under- worked. Further, if an engraved copper plate be pressed under a rolling press on a leaden plate, copper may be reduced on the latter by the electrotype process, and perfectly sharp, exact copies thus obtained.—The parts of the model which are not to be covered with copper are previously coated with wax; so likewise is the conducting wire, so far, at least, as it dips into the solution. | B. The non-conductors used as models, are wood, gypsum, porce- lain, sulphur, sealing-wax, stearic acid [this appears to be what Jacobi means by stearine]._ Gypsum must be soaked in a hot mixture of stearic acid and wax, till it no longer gives out air-bubbles. Casts of stearic acid are much sharper than those of gypsum. To give these models a conducting surface, a quantity of plumbago is rubbed up with the water to a semifluid consistence, and spread, by means of a brush, on those parts of the model which are to be coppered; after drying, the superflu- ous plumbago is rubbed off with a dry brush. Or the plumbago, in the state of dry powder, may be rubbed on the model with a brush slightly moistened with oil. Since the coating of plumbago conducts but imper- fectly, the deposition of copper is most’ abundant at the point where the plumbago touches the conducting wire. It is therefore advantageous to place a thin strip of lead or copper, connected with the conducting wire, close round the surface to be coppered. The metal must also be placed in a horizontal position—When a great degree of malleability is not desired, the growth of the layer of copper, when it has once begun to form, may be accelerated by strewing copper filings on it, which become intimately mixed with the reduced copper. The electro-type process is applicable to copper-plate engravings, medals, stereotype plates, ornaments,—and likewise to making blocks for printing calico and patterns for paper-hanging. (Jacobi.) : Methods of others. Apparatus and Liquids. Spencer's Apparatus. A cylinder of glass, wood, or glazed earthen- ware (having a rim at the bottom for retaining the gypsum), is closed at contains zinc immersed in a solution of common salt, and is itself sur- rounded by a solution of sulphate of copper, which contains the body to be coppered. The operation succeeds best when the surface to be cop-