DETERMINATION OF REFRACTIVE INDEX

DETERMINATION OF REFRACTIVE INDEX 

1. The device that is used to measure refractive index is called Refractometer. Ernst Abbe of Germany was the first scientist to develop one called Abbe’s Refractometer. 

1. The main part of Abbe’s Refractometer is prism lens. It consists of two Abbe’s prism of flint glasses of high refractive index, 1.75 cemented into mounting hollow cases. 

1. The cases act as jackets and water from the thermostat can be circulated around the prism for controlling temperature.

1. The upper face of the lower prism is mounted so that it will act as a diffusion screen, giving rays in all directions and confines a thin sample of the liquid.

1. The lower face of the upper prism, known as the refractive prism is highly polished. 

1. The two prism cases are lingered together, when the prisms are closed and touched by a locknut with a space of 0.1 to 0.14 mm between the faces of the prism. A small quantity of the sample under experiment is introduced in this narrow space.

1. The case of upper prism is rigidly attached to the index arm, which carries a scale at its upper end. The scale is graduated in terms of refractive index from 1.3 to 1.7 up to 3rd decimal.

1. A telescope is rigidly fixed into the sector which is attached to upright of base in such a way that the axis or the sector coincides with the rotation of the prism lens.

1. The prism lens can be rotated by means of the arm which can be moved by a knob. 

1. The line of demonstration corresponds to the critical angle is seen through the telescope and the index arm is rotated so that the border line passes exactly through the refractive index, thereby intersecting the cross wires. The refractive index is read through the eyepiece at the upper end.