Discovery of Proton - Study of Anode Rays

Since the atom as a whole is electrically neutral and the presence of negatively charge particles in it was established , therefore it was thought that some positively charged particles must also be present in the atom. For this purpose, Goldstein in 1886, performed discharge tube experiments in which he took perforated cathode and a gas at low pressure was kept inside the tube. 
On passing high voltage between the electrodes , it was found that some rays were coming from the side of the anode which passed through the holes in the cathode and produced green fluorescence on the opposite glass wall coated with zinc sulphide. These rays were called anode rays or canal rays or positive rays.

Origin of Anode Rays :- These rays are believed to be produced as a result of the knock out of the electrons from the gaseous atoms by the bombardment of high speed electrons of the cathode rays on them. Thus, anode Rays are not emitted from the anode but are produced in the space between the anode and the cathode.

Properties of Anode Rays :- In actual there are the same method of we discuss in cathode rays. The anode rays were found to possess the following main properties :-

1. They travel in the straight lines. However, their speed is much less than that of the cathode rays.

2. They are made up of material particles.

3. They are positively charged, as indicated by the direction of deflection of these rays in the electric and magnetic fields. That is why they are called 'positive rays' 

4. Unlike cathode rays, the ratio, charge/mass is found to be different for the particles constituting anode rays when different gases are taken inside the discharge tube. In other words, the value of charge/mass depends upon the nature of the gas taken inside the discharge tube.

5. The value of the charge on the particles constituting the anode rays is also found to be depends upon the nature of gas taken inside the discharge tube. However, the charge on these particles is found to be a whole number multiple of the charge present on the electrons. In other words , these positively charged particles may carry one, two or three units of positive charged , depending upon the number of electrons knocked out.

6. The mass of the particles constituting the anode rays is also found to be different for different gases taken in the discharge tube. However, it's value is found to be nearly equal to be that of the atom of the gas.

Hence, a proton may be defined as :- A proton may be defined as that fundamental particle which carries one unit positive charge and has a mass nearly equal to that of hydrogen atom. 

It may be mentioned here that in case of any other gas taken inside the discharge tube, the mass of the positively charged particles was found to be nearly a whole number multiple of the mass of the proton. Hence, it led to the belief that porton must be fundamental particles present in all atoms and that the atoms of gases other than hydrogen contained some whole number of protons.