Arc lamp spectra from NaCl, CaCl2, SrCl soaked rods.

White light from the carbon arc passes through a slit and is sent through a transmission diffraction grating, creating a full spectrum on a projection screen. (The 750 line-per-mm grating has the blazes cut so that most of the light is concentrated in the first order.) Step 2] Turn off the D.C. power to the carbon arc. Replace the top carbon rod with a special carbon soaked in the chloride of Sodium, Calcium, Strontium(LeC) or Lithium(PSL). Turn on the power and project a line emission spectrum superimposed upon a white light spectrum. Note to setup people: The second lens is positioned so that the image of the spectrum is focused on the screen. This insures that the spectral lines are well-focused.