LEYDEN Phial

, in Electricity, is a glass phial or jar, coated both within and without with tin foil, or some other conducting substance, that it may be charged, and employed in a variety of useful and entertaining experiments. Or even flat glass, or any other shape, so coated and used, has also received the same denomination. Also a vacuum produced in such a jar, &cs has been named the Leyden Vacuum.

The Leyden Phial has been so called, because it is said that M. Cunæus, a native of Leyden, first contrived, about the close of the year 1745, to accumulate the electrical power in glass, and use it in this way. Bu<*> Dr. Priestley asserts that this discovery was first made by Von Kleist, dean of the cathedral in Camin; who, on the 4th of November 1745, sent an account of it to Dr. Lìeberkuhn at Berlin: however, those to whom Kleist's account was communicated, could not succeed in performing his experiments. The chief cireumstances of this discovery are stated by Dr. Priestley in the following manner.

Professor Musschenbroek and his friends, observing that electrified bodies, when exposed to the common atmosphere, which is always replete with conducting particles of various kinds, soon lost the most part of their electricity, imagined that if the electrified bodies should be terminated on all sides by original electrics, they might be capable of receiving a stronger power, and retaining it a longer time, Glass being the most convenient electric for this purpose, and water the most convenient non-electric, they at first made these experiments with water in glass bottles; but no considerable discovery was made, till M. Cunæus, happening to hold his glass vessel in one hand, containing water, which had a communication with the prime conductor by means of a wire; and with the other hand disengaging it from the conductor, when he supposed the water had received as much electricity as the machine could give it, was surprised by a sudden and unexpected shock in his arms and breast. This experiment was repeated, and the first accounts of it published in Holland by Messrs. Allamand and Musschenbroek; by the Abbé Nollet and M. Monnier, in France; and by Messrs. Gralath and Rugger, in Germany. M. Gralath contrived to increase the strength of the shock, by altering the shape and size of the phial, and also by charging several phials at the same time, so as to form what is now called the electrical battery. He likewise made the shock to pass through a number of persons connected in a circuit from the outside to the inside of the phial. He also observed that a cracked phial would not re- ceive a charge: and he discovered what is now called the Residuum of a charge.

Dr. Watson, about this time, observed a circumstance attending the operation of charging the phial, which, if pursued, might have led him to the discovery which was afterwards made by Dr. Franklin. He says, that when the phial is well electrified, and you apply your hand to it, you see the fire flash from the outside of the glass, wherever you touch it, and it crackles in your hand. He also observed, that when a single wire only was fastened about a phial, properly silled with warm water, and charged; upon the instant of its explosion, the electrical corruscations were seen to dart from the wire, and to illuminate the water contained in the phial. He likewise found that the stroke, in the discharge of the phial, was, cateris paribus, as the points of contact of the non-electrics of the outside of the glass; which led to the method of co<*>ting glass: in consequence of which he made experiments, from whence he concluded, that the effect of the Leyden phial was greatly increased by, if not chiefly owing to, the number of points of non-electric in contact within the glass, and the density of the matter of, which these points consisted; provided the matter was, in its own nature, a ready conductor of electricity. He farther observed, that the explosion was greater from hot water inclosed in glasses, than from cold, and from his coated jars warmed, than when cold.

Mr. Wilson, in 1746, discovered a method of giving the shock to any particular part of the body, without affecting the rest. He also increased the strength of the shock by plunging the phial in water, which gave it a coat of water on the outside as high as it was silled within. He likewise found, that the law of accumulation of the electric matter in the Leyden phial, was always in proportion to the thinness of the glass, the surface of the glass, and that of the non-electrics in contact with its outside and inside. He made also a variety of other experiments with the Leyden phial, too long here to be related.

Mr. Canton found, that when a charged phial was placed upon electrics, the wire and coating would give a spark or two alternately, and that by a continuance of the operation the phial would be discharged; though he did not observe that these alternate sparks proceeded from the two contrary electricities discovered by Dr. Franklin.

The Abbé Nollet made several experiments with this phial. He received a shock from one, out of which the air had been exhausted, and into which the end of his conductor had been inserted. He ascribed the force of the glass, in giving a shock, to that property of it, by which it retains it more strongly than conductors do, and is not so easily divested of it as they are. It was he also who first tried the effect of the electric shock on brute animals: and he enlarged the circuit of its conveyance.

M. Monnier, it has been said, was the first who disvered that the Leyden phial would retain its electricity for a considerable time after, it was charged; and that in time of frost he found it continued for 36 hours. It is remarkable too that both the French and English philosophers made several experiments, which, with a small degree of attention, would have led them to the discovery of the different qualities of the electricity on| the contrary sides of the glass. But this discovery was reserved for the ingenious Dr. Franklin; who, in explaining the method of charging the Leyden phial, observes, that when one side of the glass is electrified plus, or positively, the other side is electrified minus, or negatively: so that whatever quantity of sire is thrown upon one side of the glass, the same quantity is drawn out of the other; and in an uncharged phial, none can be thrown into the inside, when none can be taken from the outside; and that there is really no more electric fire in the phial after it is charged than before; all that can be done by charging, being only to take from one side, and convey to the other. Dr. Franklin also observed that glass was not impervious to electricity, and that as the equilibrium could not be restored to the charged phial by any internal communication, it must necessarily be done by conductors externally joining the inside and the outside. These capital discoveries he made by observing, that when a phial was charged, a cork ball suspended by silk, was attracted by the outside coating, when it was repelled by a wire communicating with the inside, and vice versa. But the truth of this principle appeared more evident, when he brought the knob of the wire, communicating with the outside coating, within a few inches of the wire communicating with the inside coating, and suspended a cork ball between them; for then the ball was attracted by them alternately, till the phial was discharged.

Dr. Franklin also shewed, that when the phial was charged, one side lost exactly as much as the other gained, in restoring the equilibrium. Hanging a fine linen thread near the coating of an electrical phial, he observed that whenever he brought his finger near the wire, the thread was attracted by the coating; for as the fire was drawn from the inside by touching the wire, the outside drew in an equal quantity by the thread. He likewise proved, that the coating on one side of a phial received just as much electricity, as was emitted from the discharge of the other, and that in the following manner:—He insulated his rubber, and then hanging a phial to his conductor, he found it could not be charged, even when his hand was held constantly to it; because, though the electric fire might leave the outside of the phial, there was none collected by the rubber to be conveyed to the inside. He then took away his hand from the phial, and forming a communication by a wire from the outside coating to the insulated rubber, he found that it was charged with ease. In this case it was plain, that the very same fire which left the outside coating, was conveyed to the inside by the way of the rubber, the globe, the conductor, and the wire of the phial. This new theory of charging the Leyden phial, led Dr. Franklin to observe a greater variety of facts, relating both to the charging and discharging it, than other philosophers had attended to. And this maxim, that it takes in at one surface, what it loses at the other, led Dr. Franklin to think of charging several phials together with the same trouble, by connecting the outsrde of one with the inside of another; by which the fire that was driven out of the first would be received by the second, &c. By this means he found, that a great number of jars might be charged with the same labour as one only; and tha<*> they might be charged equally high, were it not that every one of them receives the new fire, and loses its old, with some reluctance, or rather that it gives some small resistance to the charging. And on this principle he first constructed an electrical battery.

When Dr. Franklin first began his experiments on the Leyden phial, he imagined that the electric fire was all crowded into the substance of the non-electric, in contact with the glass. But he afterwards found, that its power of giving a shock lay in the glass itself, and not in the coating, by the following ingenious analysis of the phial. To find where the strength of the charged bottle lay, having placed it upon a glass, he first took out the cork and the wire; but not finding the virtue in them, he touched the outside coating with one hand, and put a finger of the other into the mouth of the bottle; when the shock was felt quite as strong as if the cork and wire had been in it. He then charged the phial again, and pouring out the water into an empty bottle which was insulated, he expected that if the force resided in the water, it would give the shock; but he found it gave none. He therefore concluded that the electric sire must either have been lost in decanting, or must remain in the bottle; and the latter he found to be true; for, upon filling the charged bottle with fresh water, he found the shock, and was satissied that the power of giving it resided in the glass itsels. The same experiment was made with panes of glass, laying the coating on lightly, and charging it, as the water had been before charged in the bottle, when the result was precisely the same. He also proved in other ways that the electric sire resided in the glass. See Franklin's Letters and Observations, &c. Also Priestley's Hist. of Electricity, vol. i, pa. 191, &c.

From this account of Dr. Franklin's method of analyzing the Leyden phial, the manner of charging and discharging it, with the reason of the process, are easily understood. Thus, placing a coated phial near the prime conductor, so that the knob of its wire may be in contact with it; then upon turning the winch of the machine, the index of the electrometer, E, fixed to the conductor, will gradually rise as far as 90° nearly, and there rest; which shews that the phial has received its full charge: then holding the discharger by its glass handle, and applying one of its knobs to the outside coating of the phial, the other being brought near the knob of the wire, or near the prime conductor which communicates with it, a report will be heard, and luminous sparks will be seen between the discharger and the conducting substances communicating with the sides of the phial; and by this operation the phial will be discharged. But, instead of using the discharger, if a person touch the outside of the phial with one hand, and bring the other hand near the wire of the phial, the same spark and report will take place, and a shock will be felt, affecting the wrists and elbows, and the breast too when the shock is strong: a shock may also be given to any single part of the body, if that part alone be brought into the circuit. If a number of persons join hands, and the first of them touch the outside of the phial, while the last touches the wire communicating with the inside, they will all feel the shock at the same time. If the coated phial be held by the wire, and the outside coating be presented to the prime| conductor, it will be charged as readily; but only with this difference, that in this case the outside will be positive, and the inside negative; also if the prime conductor, by being connected with the rubber of the machine, be electrified negatively, the phial will be charged in the same manner; but the side that touches the conductor will be electrified negatively, and the opposite side will be electrified positively. But, by insulating the phial, and repeating the same process, the index of the electrometer will soon rise to 90°, yet the phial will remain uncharged; because the outside, having no communication with the earth, &c, cannot part with its own electricity, and therefore the inside cannot acquire an additional quantity: but when a chain, or any other conductor, connects the outside of the phial with the table, the phial may be charged as before. Moreover, if a phial be insulated, and one side of it, instead of being connected with the earth, be connected with the insulated rubber, whilst the other side communicates with the prime conductor, the phial will be expeditiously charged; because that whilst the rubber exhausts one side, the other side is supplied by the prime conductor; and thus the phial is charged with its own electricity; or the natural electric matter of one of its sides is thus thrown upon the other side. This last experiment may be diversified by insulating the phial, and placing it with its wire at the distance of about half an inch from the prime conductor, and holding the knob of another wire at the same distance from its outside <*>oating; then, upon turning the machine, a spark will be observed to proceed from the prime conductor to the wire of the phial, and another spark will pass at the same time from the outside coating to the knob of the wire presented towards it: and thus it appears that as a quantity of the electric matter is entering the inside of the phial, an equal quantity of it is leaving the outside. If the wire presented to the outside of the phial be pointed, it will be seen illuminated with a star; but if the pointed wire be connected with the coating of the phial, it will appear illuminated with a brush of rays. See Charge, Electrical Shock, Experiments, &c.

Mr. Cavallo has described the construction of a phial which, being charged by an electrical kite, in examining the state of the clouds, or in any other way, may be put into the pocket, and which will retain its charge for a considerable time. A phial of this kind has been kept in a charged state for six weeks. See his Electricity, pa. 340. Many other curious experiments with the Leyden phial may be seen in the books above cited, as also in the volumes of the Philos. Trans. and elsewhere. In this last-mentioned work, Mr. Cavallo describes a method of repairing coated phials that have cracked by any means. He first removes the outside coating from the fractured part, and then makes it moderately hot, by holding it to the flame of a candle; and whilst it remains hot, he applies burning sealing-wax to the part, so as to cover the fracture entirely; observing that the thickness of this wax coating may be greater than that of the glass. Lastly, he covers all the sealingwax, and also part of the surface of the glass beyond it, with a composition made with four parts of bees-wax, one of resin, one of turpentine, and a very little oil of olives; this being spread upon a piece of oiled silk, he applies it in the manner of a plaster. In this way seve- ral phials have been so effectually repaired, that after being frequently charged, they were at last broken by a spontaneous discharge, but in a different part of the glass. Philos. Trans. vol. 68, pa. 1011.