498 



CHAPTER XXV 



already described ; an oil of already determined density is poured over it, 

 and the two mixed until air-bubbles are no longer seen to rise. The stirrer 

 may conveniently be a piece of iron rod, of such a length that it may remain 

 in the vessel without interfering with the insertion of the stopper. After 

 removal of the air-bubbles, the vessel is filled up with oil and the determina- 

 tion completed, as above. An example follows : — 



Weight of vessel, stopper and stirrer . . 



.. ,, >> >, ,, a^ncl oil . . 



Specific gravity of oil (water = i -o) . . 

 Weight of oil 



„ vessel, stopper, stirrer and massecuite 



„ massecuite 



„ vessel, etc., massecuite and oil 



,, oil in space occupied by massecuite 



2095 -65 



Real specific gravity of massecuite 



1190 -lO 



Grms. 



453 -75 

 1838 -35 



o -8550 

 1384 -95 

 2548 '35 

 2095 '65 

 2743 -20 

 1190 -lO 



X o -855 = I -5056 



Fig. 331 



Determination of the Refractive Index. — The instrument most convenient 

 for this purpose is the Abbe refractometer. Fig. 331, with beatable prisms 

 as made by Adam Hilger, Ltd. The determination of the refractive index 

 is made as follows : — The instrument is brought into a horizontal position, 

 and the two prisms A and B separated by opening the milled head 

 clamp attached to the lower prism ; a drop of the material under 

 analysis is placed on one of the prisms, which are then closed and 



