APPENDIX.
NUMBER I.
A description of the Cement used for electrical purposes.
The best cement for electrical purposes is made by melting two parts of rosin, two of bee’s-wax, and one of brick-dust, or red ochre, together. This method of making cement is much preferable to that of rosin alone, as it is not so brittle, and at the same time it insulates equally well.
NUMBER II.
A Composition for Coating Cylinders or Globes.
The most approved composition for lining glass cylinders or globes, is made with four parts of Venice turpentine, one part of rosin, and one of bee’s-wax.—They must be boiled together for about two hours over a slow fire, and stirred very frequently; afterwards the composition is left to cool, when it is fit for use.
If a cylinder or globe is to be lined with this mixture, a sufficient quantity must be pulverised, and introduced into the glass; then by holding the glass near the fire, the composition is melted, and by a little skill may be spread over all its internal surface, to about the thickness of a wafer.—The glass, however, must be heated very gradually, otherwise, there is danger of its breaking in the operation.
NUMBER III.
To make the best kind of Amalgam for exciting Electrics.—
Any metal dissolved in mercury or quick-silver will answer the purpose very well, thus two parts of quick-silver with one of tin-foil, or Aurum Mosaicum, have been used to advantage. But the most powerful composition for an amalgam, is zinc and mercury, in the proportion of one part of the latter, with five of the former, to which may be added a little bee’s-wax or tallow, the proper way of preparing this amalgam is the following.—Let the quick-silver be heated, to about the degree of boiling water, and let the zinc also be melted in an iron ladle. Pour the heated quick-silver into a wooden box, and immediately afterwards pour the melted zinc into it likewise. Then shut the box, and shake it about for some time. You must now wait till the amalgam is cool, or nearly so, and then mix a little bee’s-wax, or mutton-suet with it, by trituration.
NUMBER IV.
The preparation of electrical Paint.
The electrician will very frequently have occasion to make use of paint, both for ornament, and convenience. We shall therefore describe a pigment, which, while it looks very well, insulates the instrument, and answers a variety of other purposes.—If a red colour is wished, let a piece of red sealing-wax be dissolved in a sufficient quantity of highly rectified spirits of wine, then let the substance which you intend to colour be warmed, after which the paint may be laid on by means of a hair pencil. Care should be taken to render the instrument clean and dry, especially if it be a glass one.—Two or three coats of this paint, will generally answer every purpose. If a black colour is preferred, black sealing-wax may be used.
If the outside coating of a jar is desired to be coloured, common oil paint will do much better than that above described, for here insulation is not required; a covering of some paint or other is always necessary, in order to prevent the amalgam, which is often scattered about the table where the apparatus is placed, from corroding the tin-foil with which the jar is covered.
NUMBER V.
To make the Artificial Bolognian Stone.
“Calcine some common oyster-shells, by keeping them in a good coal fire, for half an hour; let the purest part of the calx be pulverised and sifted. Mix with three parts of this powder, one part of flowers of sulphur. Let this mixture be rammed into a crucible of about an inch and a half in depth, till it be almost full; and let it be placed in the middle of the fire, where it must be kept red hot for an hour at least, and then set it by to cool: when cold turn it out of the crucible; and cutting or breaking it to pieces, scrape off, upon trial, the brightest parts; which, if good phosphorus, will be a white powder.”