A Canal ray (also known as a positive or anode ray) is described as a positive ions' beam, created by certain gas-discharge tube types. These rays were observed in 1886 in Crookes tubes when the German scientist named "Eugen Goldstein performed experiments."
Later on, anode rays work by the scientist Wilhelm Wien and J. J. Thomson led to the mass spectrometry development. So, it is said that Dempster is the one who discovered canal rays. He was also one of the first spectrometers to use such ions’ sources.
Canal Ray Experiment
The canal rays experiment is the one that led to the discovery of the proton. The proton discovery has happened after the electron discovery has further strengthened the structure of the atom. In this experiment, Goldstein happened to apply a high voltage across a discharge tube that had a perforated cathode. Also, a faint luminous ray was seen extending from the holes of the back of the cathode.
Apparatus of the Experiment
The apparatus of this experiment includes the same cathode-ray experiment, made up of a glass tube containing two metal ion pieces at different ends that acts as an electrode. These two metal pieces are further connected with an external voltage. The air evacuation lowers the pressure of the gas present inside the tube.
The Procedure of the Experiment
Let us discuss more details about the procedure of the experiment, as listed below.
As the apparatus is set up by evacuating the air and giving a high voltage source for maintaining a low pressure inside the tube.
The high voltage is passed to the two metal pieces to ionize the air by making it an electricity conductor.
Thereby, the electricity starts to flow as the circuit is complete.
When the voltage was increased to thousands of volts, a faint luminous ray was seen, extending from the holes present behind the cathode.
These rays moved in the opposite direction facing the cathode rays and were called canal rays.
When a higher voltage is applied, the experiment ionizes the gas, and it is the positive ions of gas that constitute the canal ray. It is the kernel or nucleus of the gas that is used in the tube, and thus, it has different properties to that of the cathode rays, made up of electrons.
Differences between Cathode and Anode Rays
Basically, in the first Canal ray experiment, William used the Crookes tube supplying high voltage and gradually reduced the pressure within the tube chamber from 0.01 to 0.001 atm. Also, he noticed a certain beam of light starting to emanate from the tube's cathode, and this travelled throughout the tube upon reducing the pressure further.
Then, the light emitted from the ray was passed via the strong electric field formed between two plates, charge positive and negative. The light beam was found to curve towards the positive plate and was thus charged negatively. It was named Cathode Rays because it originated from the Cathode of the Tube.
After that, using a perforated Cathode (Cathode with fine pores), he conducted another experiment. Even this time, too, he saw the light, but now, starting from the middle of the tube. Upon increasing the voltage and reducing further pressure, the beam went towards the cathode. The beam bent towards the negative plate when the light beam was placed in between an electric field, and hence, these rays were charged positively.
But we cannot call them Anode Rays since they weren't emitted from the AnodeAnode. Therefore, they were known as Canal Rays because they formed light 'canals' when they left the cathode's perforations.
Production of Anode Rays
When a high range of voltage is applied to the tube, the electric field accelerates the small ions count (electrically charged atoms) that are always present in the gas, created by natural processes like radioactivity. These collide with the gas atoms by knocking the electrons off of them and creating added positive ions. These electrons and ions strike more atoms, in turn, creating added positive ions in a chain reaction. Then, all the positive ions get attracted to the negative cathode, and a few of them pass through the holes in the cathode if any. These are known as the anode rays.
Unlike the cathode rays, canal rays will depend upon the nature of gas that is present in the tube. This is due to the canal rays being composed of positive ionized ions formed by the ionization of gas present in the tube.
The charge to the ratio of mass for the ray particles was different for different gases.
The particle's behavior in the magnetic and electric fields was opposite compared to the cathode rays.
Besides, a few particles that are charged positively carry multiples of the fundamental value of the charge.
E. Goldstein also concluded that apart from the cathode rays that pass from the negatively charged electrode to the positively charged electrode, there is another set of rays that move exactly in opposite directions which is from a positively charged electrode to a negatively charged electrode and these rays are canal or anode rays. They were further analyzed and it led to the discovery of a positively charged subatomic particle called “Proton”.