The famous Millikan's oil drop experiment in 1908 determined the magnitude of charge of the electron to be 1.59*10^(-19) C. However, it was well known that electron has a negative charge. Although there is no definition of charge per se, the original experimental identification is still Franklin's experiment i.e., whenever glass is rubbed with silk, the glass becomes negatively charged. I am searching for those original experiments which showed that the charge on the electron behaved the same way as glass rod rubbed with silk? Thanks
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$\begingroup$ Sign of charge is determined in electrolysis experiments. $\endgroup$– Alexandre EremenkoCommented Feb 16, 2019 at 0:17
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$\begingroup$ I am afraid this is not correct. Electrolysis had nothing to do with the sign of electron charge in the beginning. The sign of the electron must have been determined by electrostatic experiments. $\endgroup$– ACRCommented Feb 16, 2019 at 0:50
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$\begingroup$ In electrolysis, ions of one sign accumulate on one side, ions of other sign on another. Ion's sign is determined by whether it has an extra electron(s) or some deficient electron(s). Therefore, ANY experiment with electrolysis immediately gives you the sign of the electron charge. $\endgroup$– Alexandre EremenkoCommented Feb 16, 2019 at 0:54
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2$\begingroup$ Perhaps I am missing something but in the early days people thought of electricity as a fluid, and there was controversy as to whether there was a single fluid (Franklin) or two. Franklin, and many after him, thought of electric current as being, in fact, positively charged. But once the notion of electron got currency Crookes showed that their charge must be negative by using deflection by cathode rays in 1870-s, for example. $\endgroup$– ConifoldCommented Feb 16, 2019 at 4:11
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1$\begingroup$ @M. Farouq: This is the same vicious circle: when you charge an object to insert to your electroscope, how do you know, whether you add electrons or subtract them. It seems (from the Wikipedia article "Electron") that the charge sign was not known until electrons could be isolated (in electronic beams). $\endgroup$– Alexandre EremenkoCommented Feb 16, 2019 at 13:26
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2 Answers
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I think we have an answer. The original paper is in French by Perrin. The translation is in Nature (1896). NEW EXPERIMENTS ON THE KATHODE RAYS Jean Perrin. It is a two paged article. https://www.nature.com/articles/053298a0
With the help of magnetic deflection, he directed the cathode rays into a electroscope connected to a Faraday cylinder (see Figure 1). It is a nice experiment. In the end he concludes "In short, the Faraday's cylinder became negatively charged when the kathode rays entered it, and only when they entered it; the kathode rays are then charged with negative electricity (emphasis is his own). He does not give the details of his electroscope. However, testing the sign of the electroscope was rather an elementary experiment with charged rods.
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I believe this goes back to the Hall effect. The original experiment, carried by Hall in 1879, allows the determination of carrier densities. The original paper by Hall does not, however, mention this application so it is not clear how quickly carrier densities were determined using this method, although one would think this was done before Perrin did his own work approx 17 years later as referenced in another anwser.
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$\begingroup$ Perrin does not cite Hall. In the 1870s, the centers of Physics were in Europe and probably his did not get immediate attention. Sadly, it is cited only 23 times. $\endgroup$– ACRCommented Feb 16, 2019 at 21:48