THE ANALYSIS OF BUTTER 



77 



To make an observation, take the refractc meter 

 (Fig. 38), out of its case, stand it up, screw it in 

 the thermometer, and connect the india-rubber tubes 

 carrying the water to the inlet and outlet tubes of the 



FIG. 39. Ref ractometer 



jacket. Turn the milled head, and open and throw 

 back on to its support the lower prism ; see that both 

 glass surfaces are clean (a cloth dipped in alcohol, 

 followed by a dry soft cloth is best for cleaning), and 

 place a drop of the melted fat in the centre of the 

 surface of the lower prism (Fig. 39), and close it. 



