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
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.
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.