What experiments did Goldstein perform that hinted at protons?

Eugen Goldstein performed the canal ray (or anode ray) experiment in 1886, which hinted at the existence of protons.​

Goldstein’s Canal Ray Experiment

• Goldstein used a discharge tube with a perforated cathode (cathode with small holes).​
• When a high voltage was applied across the tube at low pressure, he observed new rays traveling in the opposite direction of cathode rays, passing through the "canals" or holes in the cathode.​
• These "canal rays" were found to be composed of positively charged particles.​
• Goldstein concluded that these rays were made from positive ions formed from the residual gas inside the tube, and their properties (like mass and charge) depended on the gas used.​
• When hydrogen gas was used, the canal rays consisted of particles with the smallest mass and greatest charge-to-mass ratio—identified later as protons.​
• This experiment indicated that atoms contained positive, massive constituents—laying the groundwork for the later, full discovery of the proton.​

Goldstein didn’t fully characterize the proton, but his work clearly hinted at its existence by producing and observing positively charged ions, including hydrogen ions (protons), in his discharge tube experiment.