Experiments on Amber, 3 July 1762
Experiments on Amber
MS not found; reprinted from Benjamin Franklin, Experiments and Observations on Electricity, 1769 edition, pp. 425–7.5
Saturday, July 3, 1762.
To try, at the request of a friend,6 whether amber finely powdered might be melted and run together again by means of the electric fluid, I took a piece of small glass tube about 2½ inches long, the bore about 1/12 of an inch diameter, the glass itself about the same thickness; I introduced into this tube some powder of amber, and with two pieces of wire nearly fitting the bore, one inserted at one end, the other at the other, I rammed the powder hard between them in the middle of the tube, where it stuck fast, and was in length about half an inch. Then leaving the wires in the tube, I made them part of the electric circuit, and discharged through them three rows of my case of bottles. The event was, that the glass was broke into very small pieces and those dispersed with violence in all directions. As I did not expect this, I had not, as in other experiments, laid thick paper over the glass to save my eyes, so several of the pieces struck my face smartly, and one of them cut my lip a little so as to make it bleed. I could find no part of the amber; but the table where the tube lay was stained very black in spots, such as might be made by a thick smoke forced on it by a blast, and the air was filled with a strong smell, somewhat like that from burnt gunpowder. Whence I imagined, that the amber was burnt, and had exploded as gunpowder would have done in the same circumstances.
That I might better see the effect on the amber, I made the next experiment in a tube formed of a card rolled up and bound strongly with packthread. Its bore was about ½ of an inch diameter. I rammed powder of amber into this as I had done in the other, and as the quantity of amber was greater, I increased the quantity of electric fluid, by discharging through it at once 5 rows of my bottles. On opening the tube, I found that some of the powder had exploded, an impression was made on the tube though it was not burst, and most of the powder remaining was turned black, which I suppose might be by the smoke forced through it from the burnt part:7 Some of it was hard; but as it powdered again when pressed by the fingers, I suppose that hardness not to arise from melting any parts in it, but merely from my ramming the powder when I charged the tube.
B.F.
5. Letter XLI in both the 1769 edition and that of 1774, where it is printed on pp. 435–7. While this paper is called a “Letter,” and has the date and initialed signature in the usual places, it carries no salutation or complimentary close, and no addressee is indicated.
6. Identified in Barbeu Dubourg, Oeuvres de M. Franklin (Paris, 1773), I, 243, as John Pringle, presumably on information supplied by BF.
7. In some degree these experiments supported Ebenezer Kinnersley’s with gunpowder and his conclusion that electricity “will, by its violent Motion and the Resistance it meets with, produce Heat in other Bodies, when passing thro’ them, provided they be small enough”; above, IX, 290. BF highly praised Kinnersley’s “beautiful experiment” and agreed that it disproved what he himself had previously called “a cold fusion”; above, p. 48.