If an electrical Cake is dipp'd in Water, it is thereby made a Conductor of Electricity, the Water hanging about it transmitting the electrical Effluvia in such a manner, that a Person standing thereon can by no means be electrified enough to attract the leaf Gold at the smallest Distance; though the Person standing upon the same Cake when dry, attracted a Piece of fine Thread hanging at the Distance of two Feet from his Finger. We must here observe that the Cake being of an unctuous Substance, the Water will no where lie uniformly thereon, but adhere in separate Moleculæ; so that in this Instance the Electricity jumps from one Particle of Water to another, till the Whole is dissipated.
From the Appearance of the Threads amongst which I rub the Tube, I can frequently judge, though the Spirit may be many Feet distant from them, whether or no it will fire; because when the Persons standing upon the Wax are made electrical enough to fire the Spirit, the Threads repel each other at their lower Parts, where they are not confin'd, to a considerable Distance, and this Distance is in Proportion as the Threads are made electrical.
If two Persons stand upon electrical Cakes at about a Yard's Distance from each other, one of which Persons, for the Sake of Distinction, we will call A, the other B: If A when electrified touches B, A loses almost all his Electricity at that Touch only, which is receiv'd by B and stopp'd by the electrical Cake; if A is immediately electrified again to the same Degree as before and touches B, the Snapping is less upon the Touch; and this Snapping, upon electrifying A, grows less and less, till B being impregnated with Electricity, though receiv'd at Intervals, the Snapping will no longer be sensible.
That Glass will repel and not conduct the Electricity of Glass, has been mention'd by others, who have treated of this Subject; but the Experiments to determine this Matter must be conducted with a great deal of Caution; for unless the glass Tube, intended to conduct the Electricity, be as warm as the external Air, it will seem to prove the contrary, unless in very dry Places and Seasons. Thus, I sometimes have brought a cold, though dry, Glass Tube near three Feet long into a Room, where there has been a Number of People; when upon placing the Tube upon Silk Lines, and laying some Leaf Silver upon a Card at one End and rubbing another Glass Tube at the other, the Silver has, contrary to Expectation, been thrown off as readily as from an Iron Rod. At first I was surpriz'd at this Appearance, but then conjectur'd, that it must arise from the Coldness of the Glass, condensing the floating Vapour of the Room; in Order then to obviate this, I warm'd the Tube sufficiently, and this Effect was no longer produced, but the Silver lay perfectly still.
If a Number of Pieces of finely spun Glass cut to about an Inch in Length, little bits of fine Wire of the same Length of what Metal you please, and small Cork Balls, are either put all together, or each by themselves, into a dry pewter Plate, or upon a Piece of polish'd Metal, they make in the following Manner a very odd and surprizing Appearance. Let a Man, standing upon electrical Cakes, hold this Plate in his Hand with the bits of Glass, Wire, &c. detached from each other, as much as conveniently may be; when he is electrified, let him cause a Person standing upon the Ground to bring another Plate, his Hand, or any other Non-Electric, exactly over the Plate containing these Bodies. When his Hand, &c. is about eight Inches over them, let him bring it down gently: As it comes near, in proportion to the Strength of the Electricity, he will observe the bits of Glass first raise themselves upright; and then, if he brings his Hand nearer, dart directly up and stick to it without snapping. The bits of Wire will fly up likewise, and as they come near the Hand, snap aloud; you feel a smart Stroke, and see the Fire arising from them to the Hand at every Stroke; each of these, as soon as they have discharged their Fire, falls down again upon the Plate. The Cork Balls also fly up, and strike your Hand, but fall again directly. You have a constant Succession of these Appearances as long as you continue to electrify the Man, in whose Hand the Plate is held; but if you touch any part either of the Man or Plate, the Pieces of Glass, which before were upon their Ends, immediately fall down.
Some few Years ago, Sir James Lowther brought some Bladders fill'd with inflammable Air, collected from his Coal-mines, to the Royal Society. This Air flam'd upon a lighted Candle being brought near it. This Inflammability has occasion'd many terrible Accidents. Mr. Maud, a worthy Member of this Society, made at that Time by Art, and shew'd the Society, Air exactly of the same Quality. I was desirous of knowing if this Air would be kindled by electrical Flashes. I accordingly made such Air by putting an Ounce of Filings of Iron, an Ounce of Oil of Vitriol and four Ounces of Water into a Florence Flask; upon which an Ebullition ensued, and the Air, which arose from these Materials, not only fill'd three Bladders, but also, upon the Application of the Finger of an Electrified Person, took Flame and burnt near the Top and out of the Neck of the Flask a considerable Time. When the Flame is almost out, shake the Flask and the Flame revives. You must with your Finger dipped in Water, moisten the Mouth of the Flask as fast as it is dried by the Heat within, or the Electricity will not fire it: Because the Flask being an Electric per se will not snap at the Application of the Finger, without the Glass being first made non-electric by wetting. It has sometimes happen'd, if the Finger has been applied before the inflammable Air has found a ready Exit from the Mouth of the Flask, that the Flash has fill'd the Flask, and gone off with an Explosion equal to the firing of a large Pistol, and sometimes indeed it has burst the Flask. The same Effect is produced from the Spirit of Sea Salt, as from Oil of Vitriol; but as the Acid of Sea Salt is much lighter than that of Vitriol, there is no Necessity to add the Water in this Experiment.
Those who are not much acquainted with Chemical Philosophy, may think it very extraordinary, that from a Mixture of cold Substances, which both conjunctly and separately are uninflammable, this very inflammable Vapour should be produced. In order to solve this, it may not be improper to premise, that Iron is compounded of a Metallic as well as a sulphurous Part. This Sulphur is so fix'd, that, after heating the Iron red hot, and even melting it ever so often, the Sulphur will not be disengaged therefrom: But upon the Mixture of the Vitriolic Acid, and by the Heat and Ebullition which are almost instantly produced, the Metallic Part is dissolved, and the Sulphur, which before was intimately connected therewith, being disengaged, becomes volatile. This Heat and Ebullition continues 'till the Vitriolic Acid is perfectly saturated with the Metallic Part of the Iron, and the Vapour once fired continues to flame, until this Saturation being effected, no more of the Sulphur flies off.
I have heretofore mentioned, how considerably perfectly dry Air conduces to the Success of these Experiments; but we have been lately informed by an Extract of a Letter, that Abbé Nolet was of Opinion, that they would succeed in wet Weather, provided the Tubes were made of Glass, tinged blue with Zaffer. I have procured Tubes of this Sort, but, after giving them many candid Trials, I cannot think them equal to their Recommendation. I first tried one of them in a smart Shower of Rain after a dry Day, when the Drops were large, and the Spirit fired three Times in about four Minutes; the same Effect succeeded, under the same Circumstances, from the white one; but after three or four Hours raining, when the Air was perfectly wet, I never could make it succeed. And to illustrate this Matter further, I have been able when the Weather has been very dry, with once rubbing my Hand down this blue Tube, and applying it to the End of an Iron Rod six Feet long, to throw off several Pieces of Leaf-Silver lying upon a Card at the other End of this Rod, whereas I never have been able to throw it off by any Means in very wet Weather. Besides, I am of Opinion, that after the Electrical Fire is gone from the Tube, the Tube has no Share in the conducting of it; my Sentiments on that Head I laid before you in a former Paper: For if the Silk Lines are wetted, they diffuse all the Electricity, and the same Effects happen when the Air is wet, be your Glass of what Colour it will. It may not be improper here to observe, that Zaffer, which is used by the Glass-makers and Enamellers, is made of Cobalt or Mundick calcin'd after the subliming the Flowers. This being reduced to a very fine Powder, and mixt with twice or thrice its own Weight of finely powdered Flints, is moisten'd with Water and put up in Barrels, in which it soon runs into a hard Mass and is call'd Zaffer.
A dry Sponge hanging by a Pack-thread at the End of an electrified Sword, or from the Hand of an electrified Man, gives no Signs of being made electrical; if it is well soak'd in Water, wherever it is touched, you both see and feel the electrical Sparks. Not only so, but if it is so full of Water, that it falls from the Sponge, those Drops in a dark Room, receiv'd upon your Hand, not only flash and snap, but you perceive a pricking Pain. If you hold your Hand, or any non-electrical Substances, very near, the Water which had ceased dropping when the Sponge was not electrified, drops again upon its being electrified, and the Drops fall in Proportion to the receiv'd Electricity, as though the Sponge were gently squeez'd between your Fingers. I was desirous to know if I was able to electrify a Drop of cold Water, dropping from the Sponge, enough to fire the Spirit; but after many unsuccessful Trials, I was forced to desist; because the cold Water dropping from the Sponge not only cool'd the Spirit too much, but also render'd it too weak; likewise, every Drop carried with it great Part of the Electricity from the Sponge. I then consider'd, in what Manner, I could give a Tenacity to the Water, sufficient to make the Drops hang a considerable Time, and this I brought about by making a Mucilage of the Seeds of Fleawort. A wet Sponge then, squeez'd hard and fill'd with this cold Mucilage, was held in the Hand of an electrified Man, when the Drops forced out by the Electricity, assisted by the Tenacity of the Liquor, hung some Inches from the Sponge, and by a Drop of this I fir'd not only the Spirit of Wine, but likewise the inflammable Air before mentioned, both with and without the Explosion. What an extraordinary Effect is this! That a Drop of cold Water (for the Seeds contribute nothing but add Consistence to the Water) should be the Medium of Fire and Flame.
Camphor is a vegetable Resin, and of Consequence an Electric per se. This Substance, notwithstanding its great Inflammability, will not take fire from the Finger of a Man or any other Body electrified, though made very warm and the Vapours arise therefrom in great Abundance. Because, neither Electric's per se excited, or electrified Bodies, exert their Force by snapping upon Electric's per se, though not excited. If you break Camphor small and warm it in a Spoon, it is not melted by Heat like other Resins; but if that Heat were continued it would all prove volatile. To Camphor thus warm'd, the Finger of an electrified Man, a Sword or such-like, will in snapping exert its Force upon the Spoon, and the circum-ambient Vapour of the Camphor will be fired thereby, and light up the whole Quantity exposed. The same Experiment succeeds by the repulsive Power of Electricity.