Thursday, February 10, 2011

The Toussaint Colorimeter

                                       TOUSSAINT COLORIMETER 

           This instrument works on quite a different system. in this case the pattern which is to be examined is illuminated by a strong strong standard white light. The light which is reflected from the pattern is collected by a lens and is passed through a color filter.Suppose this filter to be green and the pattern to be scarlet in color but the small amount of light which does pass through is directed on to the sensitive surface of a photo electric cell.
              The photo electric cell consists of a glass bulb which is filled with the inert GSA argon at low pressure . On one half of its inner surface there is a thin layer of potassium. Inside the bulb set at a small distance from the potassium there is a square of tungsten wire . The tungsten wire is connected to the negative . There is this an electric circuit consisting of the interval between the tungsten and the potassium.
              When a beam of light falls on the potassium this layer emits electrons which journey across the break in the circuit from the potassium layer to the tungsten wire thus causing the amount of current passing through the circuit to increase very considerably . The number of electrons emitted by the potassium is in exact proportion to the amount of light falling on it . If therefore Anny electrical measuring instrument such as a galvanometer is placed the circuit threading of the galvanometer shows the amount of light falling on the cell . The instrument therefore constitutes a very delicate and exact electric eye .The amounts of light passing through the red filter can be measured in terms of an electric current going through the circuit.