ELECTRICITY.

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chalk mixed together in amass like paste. The best kind ofamalgam ft that of Dr. Higgins, composed of zinc and quick-silver; if a little ot the latter Ik- added to melted zinc, it rendersit easily pulverable, and more quicksilver must be added to thepowder, if we want to make a very soft amalgam. It is apt tocrystallize by keeping, which seems in some measure to be pre-vented by triturating it with a small proportion of grease : and it isalways of advantage to triturate it before using. The proportionprescribed by l)r. Higgins, is one part of zinc to four or five partsof mercury. Aurum mosaicum, or mosaic gold, will answer near-ly as well, though it is not quite so cleanly. The rubber shouldbe supported by a spring ; by which it will easily suit any ine-qualities that may be on the surface of the glass; and by a screw,it may be made to press more or less as occasion requires. Itshould also be insulated in the most perfect manner; as, when in-sulation is not required, it may be easily taken off' by a chain orwire lumg upon it. ami thus communicate with the earth or anv uu-electrified body ; but where there is no contrivance for insulatingthe rubber, it is impossible to perform many of the most curiouselectric expei iments.

The Prime Conductor, is an insulated conducting substance,furnished with one or more points at one end, to collect the elec-tricity immediately from the electric. When it is wanted of amoderate size, it is usual to make it of hollow brass ; but when itis intended to be very large, then, on account of the price of thematerials, it is made of pasteboard covered with tin-foil ®r giltpaper. It is generally cylindrical, and should alwavs be madeperfectly free from points or sharp edges: and if holes are to bemade in it, which on many accounts are very convenient, theyshould be well rounded, and made perfectly smooth. That endof it which is at the greatest distance from the electric ought to bemade larger than the rest, as the strongest exertion of the electricfluid to escape from the conductor is always at that end. Thelarger the prime conductor is, the longer and denser a spark can bedrawn from it, the quantity- of electricity discharged i;i a spark,being nearly proportional to the size of the conductor. On thisaccount, the prime conductor is now made much larger than for-merly. Its size, however, may be so large, that the dissipation ofthe electricity from its surface, may he greater than the electriccan supply; in which case, the increase of size would only renderit an unwieldy and unnecessary incumbrance. Besides the abovementioned parts, it is necessary to have a strong frame to supportthe electric, the rubber, and the wheel. The prime .conductorshould be supported by pillars of glass or baked wood, and not by-silk strings, which admit of continual motion. In short, the ma-chine, the prime conductor, and any other apparatus actually used,should be made to stand as steady as possible, otherwise many in-conveniences will arise. livery electrician should be providedwith glass tubes of different sizes, a pretty large, stick of sealing-wax, or a glass tube covered with sealing-wax, for the negativeelectricity. lie should, at least, not be without a glass tube aboutthree feet long, and one and a half inch in diameter. This tubeshould be closed at one end, and at the other end should havefixed a brass cap with a stop-cock; which is useful in case it shouldbe required to condense or rarefy tlie air within the tube. Thebest rubber for a tube of smooth glass is the rough side of blackoiled silk, especially when it has some amalgam rubbed upon it;but the best rubber for a rough glass tube, a stick of baked wood,sealing-wax, or sulphur, is soft new- flannel. T!»e most properinstruments for what is called the accumulation of electricity arecoated electrics; among which, glass coated with conductors ob-tains the principal place: oil account of its strength, it may be form-ed into any shape, and it will receive a very great charge. Theform of the glass is immaterial with respect to the charge it willcontain; its thickness only is to be considered : for the thinner itis, the more easily will it receive the utmost charge it can bear;but it is at the same time more subject to be broken. For thisreason, a thin coated jar or plate may be used very well by itself,and it is very convenient for many experiments ; but when largebatteries are to be constructed, it is necessary to use glass a littlethicker, and care should be taken to have them perfectly well an-nealed. The most useful jars are thin cvlindrical glass vessels,about four inches in diameter, and fourteen in height, coated'vithin and without with tin foil, which is stuck on with gum-water,paste, or wax, excepting two inches of the rim or edge, which isleft bare, to prevent the communication between tire coatings. A-

bout four inches from the bottom, within, is a large cork, that re-ceives a thick wire, ending in several ramifications,which touch theinside coating ; the upper end of the wire terminating v ith a knob,considerably above the mouth of the jar, Plate T.X 111, fig, 3. Whenit is required to lie charged, it may be held in the hand, or placedon an uninsulated table, and the knob of the wire applied to theconductor; the inside coated surface becomes possessed ot the elec-tricity of the conductor, and the external surfa.ee acquires thecontrary electricity, b\ means of its uninsulated coating. \\ hen ajar of this kind is highly charged, it will discharge spontaneouslyover the uncoated surface, and seldom through the glass, whereas,when the uucoated suiface is large, it is more apt to break by thatmeans, and become useless. Yet, there is no certainty that ajar,which lias discharged itself < ver its surface, will not at ano'hertime break by a discharge through the glass, as the com rare oitenhappens. If paper covered with tin-foil be used tor the coating,with the paper next the glass, the jar will be less LaHe to break.Ajar of considerable thickness, with a neck like a bottle, in whichis cemented a thick tube to receive the wire, will sustain a veryhigh charge, and produce much greater effects than one rf thelast description. The charging wire being inserted loosely intothe tube, will fall out on inverting the jar, and the charge will re-main for several weeks without much loss. A jar thus charged,may be put into the pocket, and applied to many purposes that thecqmnie.ii jar cannot be used for. If the inside ot the jar be con-siderably damped, by blowing into it, through’ a tube reaching to •the bottom, it will’take a charge nearly one-third greater than intile ordinary state.

If a Battery be required of no very great power, as contain-ing about eight or nine square feet of coated glass, common pintor half-pint phials may be used. They may be easily coated with' tin-foil, sheet lead, or gilt paper, on the outside, and brass filings1 on tlie inside: they occupy a smalt space, and, on account of (heirthinness, hold a very- good charge. But when a large battery isrequired, these phials cannot be used, for they break very easily ;and for that purpose, cyl ndrical glass jars of about 13 inches high,and four or live inches in diameter, are the most convenient. SeePlateLXllI. lig. 4. hi coating glass plates or jars,which have a suffi-ciently large opening, the best method is to coat them with tin-foilon both sides, which may be fixed upon the glass with varnish, gumwater, bees wax, book-binder’s paste, Ac but if the jars havenot an aperture large enough to admit the tin-foil, and an instru-ment to adapt it to the surface of the glass, then brass filings maybe advantageously used. These may be stuck on with gum water,bees wax, Ac. but not with varnish, for this is apt to be set on fireby the discharge. Care must lie taken that the coatings do notcome very near the mouth of the jar, tor that will cause the jar todischarge itself. If the coaling be about two inches below the top,it will in general do very well: but there are some kinds of glass,especially tinged glass, that when coated and charged, have theproperty of discharging themselves more easily than others, evenwhen the coating is five or six inches below the edge*. W lien a jardischarges itself, the electric fluid runs from the inside to the out-side coating over the surface of the glass where it leaves an inde-lible mark all along its path, generally of a zig-zag form. There isanother sort of glass, like that of winch Florence flasks are made,which, on account of some unvitrilied panicles in its substance, isnot capable of holding tJit? least charge. On these accounts, there-fore, when a great number of jars are to be chosen for a large bat-tery, it is adviseable to try some of them first, so that their qualityand power may be ascertained. Many attempts have been madeby electricians to find some other electric, which might answerbetter than glass for this purpose, at least in point of cheapness ;but, except Father Beccaria’s method, which may be used verywell, no remarkable discovery has been made relating to this point,lie took equal quantities of very pure < olophonium, and powderof marble, sifted exceedingly fine, and kept them in a hot place aconsiderable time, where they became perfectly free from moisture.he then mixed them, and melted the composition in a proper vesselover the fire; and, when melted, poured it upon a table, 4 uponwhich he had previously stuck a piece of tin-foil, reaching withintwo or three inches of the edge of the table.- lie then, with a hotiron spread the mixture all over the table as equally as possible, tothe thickness of one-tenth of an inch : he aftei wards coated it withanother piece of tin-foil reaching within about two inches of theedge of the mixture: iu short, he coated a plate ot this mixture