merwin: media of high refraction 



39 



boil away. The mixture remaining can be powdered and heated 

 with either sulfur or AsoSs to produce a mixture having the desired 

 refractive index. 



Permanent standard resinous media, n = 1.51^6 to 1.682. Any 

 proportions of piperine and rosin form a homogeneous fusion 

 which cools to a transparent, resinous mass. Figure 1 shows the 

 refractive indices of various mixtures. On account of the strong 

 dispersion of piperine the refractive indices of minerals appar- 

 ently matched with those of mixtures rich in this constituent 

 are 0.005 to 0.01 too low. To correct the error a screen made 

 of a thin film of 7 per cent antimony iodide and 93 per cent 

 piperine should be used over the eye-piece. Any amber-colored 

 rosin in lumps is suitable. 



TABLE 2 



Permanent standard resi7ious media, n = 1.510 to 1.546. This 

 series is prepared from rosin and camphor. Each per cent of 

 camphor present lowers the refractive index 0.0007. Not more 

 than 40 per cent of camphor may be present without causing 

 crystallization. The rosin is weighed out and melted slowly, 

 when it is partly cooled but not yet hard, the camphor (well 

 crushed) is stirred in. Heat is then apphed gently and stirring 

 is continued till the camphor is dissolved. Camphor does not 

 volatilize appreciably from the cold mixtures if they are kept in 

 stoppered containers. 



Permanent standard fluids, n = 1 .487 to 1 .683. Several organic 

 solids have been found which form eutectic mixtures melting 

 much below ordinary temperatures. By plotting on cross-section 



