Abstract: The Bohr theory was verified experimentally by Franck and Hertz in 1914 ,by passing a beam of electrons accelerated by an electric field through gases. At first, the electron beam was passed through mercury vapor .The electrons collide with the mercury atoms. These collisions may be of any one of two kinds. One kind in elastic collisions which do not change the velocity or energy of the electrons, and only change the direction of their velocities. The other kind is inelastic collisions in which the electrons transfer some of their energy to the mercury vapor. A similar effect is observed with neon gas. The process of absorbing energy from electron collisions produces visible evidence. When the accelerated electrons excite the electrons in neon to upper states, they de-excite in such a way as to produce a visible glow in the gas region in which the excitation is taking place. By extension, conducting this experiment on different materials allows the energy level of the electrons in a material to be discovered. Materials might be identified in this way. A sample could be experimented on and the energy level of the material discovered and compared to know materials thus revealing its identity.