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electrician knows that a globe wet within will afford little or no fire, but the reason has not before been attempted to be given, that I know of.

34. So if a tube lined with a non-electric* be rubbed, little or no fire is obtained from it. What is collected from the hand in the downward rubbing stroke, entering the pores of the glass, and driving an equal quantity out of the inner surface into the non-electric lining : and the hand in passing up to take a second stroke, takes out again what had been thrown into the outer surface, and then the inner surface receives back again what it had given to the nonelectric lining. Thus the particles of electrical fluid belonging to the inside surface go in and out of their pores every stroke given to the tube. Put a wire into the tube, the inward end in contact with the non-electric lining, so it will represent the Leyden bottle. Let a second person touch the wire while you rub, and the fire driven out of the inward surface when you give the stroke, will pass through him into the common mass, and return through him when the inner surface resumes its quantity, and therefore this new kind of Leyden bottle cannot be so charged. But thus it may: after every stroke, before you pass your hand up to make another, let a second person apply his finger to the wire, take the spark, and then withdraw his finger; and so on till he has drawn a number of sparks ; thus will the inner surface be exhausted, and the outer surface charged; then wrap a sheet of gilt paper close round the outer surface, and grasping it in your hand you may receive a shock by applying the finger of the other hand to the wire : for now the vacant pores in the inner surface resume their quantity, and the overcharged pores in the outer surface discharge that overplus ; the equilibrium being restored through your body, which could not be restored through the glass. If the tube be exhausted of air, a non-electric lining, in contact with the wire, is not necessary; for in vacuo the electrical fire will fly freely from the inner surface without a non-electric conductor : but air resists in motion ; for being itself an electric per se, it does not attract it, having already its quantity. So the air never draws off an electric atmosphere from any body, but in proportion to the non-electrics mixed with it: it rather keeps such an atmosphere confined, which from the mutual repulsion of its particles, tends to dissipation, and would immediately dissipate in vacuo. And thus the experiment of the feather inclosed in a glass vessel hermetically sealed, but moving on the approach of the rubbed tube is explained. When an additional quantity of the electrical fluid is applied to the side of the vessel by the atmosphere of the tube, a quantity is repelled and driven out of the inner surface of that side into the vessel, and there affects the feather, returning again into its pores, when the tube with its atmosphere is withdrawn; not that the particles of that atmosphere did themselves

• Gilt paper, with the gilt face next the glass, does well.

pass through the glass to the feather. And every other appearance I have yet seen, in which glass and electricity are concerned, are, I think, explained with equal ease by the same hypothesis. Yet, perhaps, it may not be a true one, and I shall be obliged to him that affords me a better.

35. Thus I take the difference between non-electrics and glass, an electric per se, to consist, in these two particulars. 1st. That a nonelectric easily suffers a change in the quantity of the electric fluid it contains. You may lessen its whole quantity, by drawing out a part, which the whole body will again resume ; but of glass you can only lessen the quantity contained in one of its surfaces; and not that, but by supplying an equal quantity at the same time to the other surface : so that the whole glass may always have the same quantity in the two surfaces, their two different quantities being added together. And this can only be done in glass that is thin; beyond a certain thickness we have yet no power that can make this change. And, 2dly., that the electric fire freely removes from place to place, in and through the substance of a non-electric, but not so through the substance of glass. If you offer a quantity to one end of a long rod of metal, it receives it, and when it enters, every particle that was before in the rod pushes its neighbour quite to the farther end, where the overplus is discharged ; and this instantaneously where the rod is part of the circle in the experiment of the shock. But glass, from the smallness of its pores, or stronger attraction of what it contains, refuses to admit so free a motion ; a glass rod will not conduct a shock, nor will the the thinest glass suffer any particle entering one of its surfaces to pass through to the other.

53. Hence we see the impossibility of success in the experiments proposed, to draw out the effluvial virtues of a non-electric, as cinnamon, for instance, and mixing them with the electric fluid. to convey them with that into the body, by including it in the globe, and then applying friction, &c. For although the effluvia of cinnamon, and the electric fluid should mix within the globe, they would never come out through the pores of the glass, and so go to the prime conductor; for the electric fluid itself cannot come through; and the prime conductor is always supplied from the cushion, and that from the floor. And besides, when the globe is filled with cinnamon, or other non-electric, no electric fluid can be obtained from its outer surface, for the reason before-mentioned. I have tried another way which I thought more likely to obtain a mixture of the electric and other effluvia together, if such a mixture had been possible. I placed a glass plate under my cushion, to cut off the communication between the cushion and floor ; then brought a small chain from the cushion into a glass of oil of turpentine, and carried another chain from the oil of turpentine to the floor, taking care that the chain from the cushion to the glass touched no part of the frame of the machine. Another chain was fixed to the prime conductor, and held in the hand of a person to be electrified. The ends of the two chains in the glass were near an inch distant from each other, the oil of turpentine between. Now the globe being turned, could draw no fire from the floor through the machine, the communication that way being cut off by the thick glass plate under the cushion : it must then draw it through the chains whose ends were dipped in the oil of turpentine. And as the oil of turpentine being an electric per se, would not conduct, what came up from the floor was obliged to jump from the end of one chain to the end of the other, through the substance of that oil, which we could see in large sparks, and so it had a fair opportunity of seizing some of the finest particles of the oil in its passage, and carrying them off with it: but no such effect followed, nor could I perceive the least difference in the smell of the electric effluvia thus collected, from what it has when collected otherwise ; nor does it otherwise affect the body of a person electrified. I likewise put into a phial, instead of water, a strong purgative liquid, and then charged the phial, and took repeated shocks from it, in which case every particle of the electrical fluid must, before it went through my body, have first gone through the liquid when the phial is charging, and returned through it when discharging, yet no other effect followed than if it had been charged with water. I have also smelt the electric fire when drawn through gold, silver, copper, lead, iron, wood, and the human body, and could perceive no difference: the odour is always the same where the spark does not burn what it strikes ; and therefore I imagine it does not take that smell from any quality of the bodies it passes through. And indeed, as that smell so readily leaves the electric matter, and adheres to the knuckle receiving the sparks and to other things, I suspect that it never was connected with it, but arises instantaneously from something in the air acted upon by it: for if it was fine enough to come with the electric fluid through the body of one person, why should it stop on the skin of another?

But I shall never have done, if I tell you all my conjectures, thoughts, and imaginations on the nature and operations of this electric fluid, and relate the variety of little experiments we have tried. I have already made this paper too long, for which I must crave pardon, not having time now to abridge it. I shall only add, that as it has been observed here that spirits will fire by the electric spark in the summer time, without heating them, when Fahrenheit's thermometer is above 70; so when colder, if the operator puts a small flat bottle of spirits in his bosom, or a close pocket with the spoon, some little time before he uses them, the heat of his body will communicate warmth more than sufficient for the purpose.

PROFESSOR SCHÖENBEIN's Experiments: and his Remarks on Dr.

Faraday's Hypothesis on the Causes of the Inactivity of Iron in Nitric Acid.

(Continued from page 41). The explanation given by Faraday of the passive condition of iron in nitric acid of certain strength is, in the first place, that the metal becomes surrounded by a thin film of oxide; and secondly, that this oxide is not soluble in such nitric acid. Therefore, according to this view, the sole cause of the inaction would be merely a mechanical obstruction ; or in other words, the metallic iron and the acid do not coine into contact with each other. Faraday, also, seems to give a similar explanation to the following fact, which I have observed, viz.: when a voltaic circuit is completed, oxygen gas is liberated at the positive iron wire.

To this strange doctrine I must first remark, that the surface of a piece of iron rendered inert in nitric acid of the specific gravity 1:35, exhibits a pure metallic surface, much brighter than by any other mode of cleaning; and no trace of oxide is observable by the closest inspection. I will not, however, dwell upon this topic, although I am aware that it deserves consideration. In one of my former essays, I stated that iron wire made passive towards nitric acid, by any mode whatever, operates like cominon iron, in other nitric acid considerably diluted : whilst an iron wire acting in the capacity of a positive pole, exhibits an absolute chemical indifference to nitric acid of all strengths. This fact appears to me to argue forcibly against the English philosopher's hypothesis : for if we were to suppose that, at the moment of immersion of the iron wire in the dilute acid, a thin layer of this questionable oxide is formed, and that from this circumstance the liberation of gas originates, we cannot conceive how this oxide can remain even a moment in dilute acid without being dissolved in it; that is, in an acid so diluted that, according to Faraday, the oxide cannot remain indifferent and unaltered. If, for instance, the chemical indifference of the iron to the nitric acid were materially influenced by the degree of dilution of the latter, the iron, under the circumstances alluded to, would remain active, a nitrate of iron would be formed, and no liberation of oxygen from the metal would occur. Experience, however, proves that precisely the reverse happens, which is exceedingly unfortunate for the hypothesis. It is true, Faraday mentions that iron in nitric acid (without giving us any idea of its strength), is dissolved, even when it operates in the capacity of a positive pole in it. According to my experiments, which were conducted with the greatest possible care, no trace of the metal is dissolved under these circumstances, although the nitric acid be diluted with several times its own quantity of water. I kept an iron wire, which was connected

• Poggendorff's " Annalen der Physik and Chemie,” b. xxxix.

with the positive pole of a couronne des tasses of fifteen cups, for many hours in such an acid liquor; after which not the slightest trace of iron could be detected in it. If, however, another acid of the common strength, of the s. g. 1:35, for instance, be added, the result becomes modified, and a little oxide of iron is always to be found in the liquor. But I do not consider that this oxide is formed in the acid ; it appears to be produced on that part of the wire which is above the surface of the acid, by the acid vapours which are continually rising; and the nitrate thus formed is conducted to the acid below by capillary attraction.

A more important fact to which I must now solicit attention is, that the iron wire which dips into the diluted acid and is indifferent to it, becomes acted on the moment the electric current ceases to be transmitted through it. If, for instance, we were to allow the iron wire to remain in the acid to be examined, and then to interrupt the electric current, immediately a dark yellowish brown matter, which is nitrate of iron, forms around the wire. From these facts it appears that the most essential cause of the chemical indifference of iron to nitric acid, is due to the influence of the electric current, and not any surrounding thin pellicle of oxide, nor to any certain quantity of water in the acid. It is obvious, also, that if the indifference of the positive iron wire was owing to a thin enveloping oxide, the same wire ought to remain passive when separated from the pole and immersed in common nitric acid : such, however, is not the case.

The circumstance that the positive iron wire is acted upon similarly in other dilute acids as in the nitric acid is rather unfavourable to Faraday's hypothesis. It is known that iron becomes completely passive by merely dipping it into fuming nitric acid : by what means then, is the pellicle of oxide formed in such cases? I can see no means but by decomposition of the nitric acid, because no other appears to be possible. I must doubt, however, that such an action takes place; and if it does not, it would be difficult to ascertain the origin of the iron's oxidation I will bere state that the galvanometer indicates a feeble electric current when the iron is dipped into highly concentrated nitric acid : but this does not prove the oxidation of the metal. I will add one other remark, which I think is not unimportant in this subject. In my last paper I mentioned the action of an acid of 1:35 upon the iron, which took place by sudden fits, which I stated was occasioned by the metal becoming active and passive alternately. Faraday would explain this phenomenon on the supposition that at one instant a film of oxide is formed around the wire, and thus protects it from the action of the acid; and the next moment the oxide is dissolved in the acid, and the metal exposed to its action. But such an explanation forms a contradiction in itself; because it first supposes the film of oxide to be insoluble, and afterwards soluble in the nitric acid, which is an absurdity. Moreover, one might propose the following unanswerable question. Why is iron rendered passive by frequent immersions in

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