II 



BUTTER 



H7 



determinations of temperature. When, however, the differences 

 are greater than this the refractometer scale must be readjusted. 

 For this purpose the newer butter refractometers are provided 

 with a micrometer screw, which can also easily be attached to 

 the older instruments. The arrangement of this micrometer 

 screw is seen in Fig. 59 below. 



Refractometer Numbers for the Standard Liquid. 



From the table given above it is seen what number of 

 divisions ought to be given with the standard liquid at the 

 temperature shown on the thermometer. Suppose this number 

 to be 76-7. The nut, G, on the 

 micrometer screw is loosened, 

 and the nickel disc, S, turned 

 until the critical line seen in 

 the eye-piece falls exactly upon 

 the whole division of the scale 

 in this case 76. Then the 

 small black cylinder, F, which 

 is now loose, is turned until the 

 pointer, J, shows the desired 



tenths of a degree in this case 7. The loose nut, G, is then 

 screwed tight, and the accuracy of the refractometer again 

 tested. 



Naturally, the refractometer can be used for all liquids the 

 refractive index of which falls between 1-418 and T492, and it 

 also serves for substances which can be brought into a fluid 

 state by warming or by solution. 



The table given below serves to convert the scale divisions 

 into refractive indices at 25 C. In column A w are shown the 



L 2 



FIG. 59 The Micrometer Screw. 



