The Calibration of Burettes. 



89 



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The principle of the method consists in caiising a constant 

 volume of liquid to slide in the burette (so that it may be 

 made to assume any desired position therein) and then reading 

 ofp its length in terms of the burette divisions. 



In Fig. 1 the burette B is attached by means of caoutchouc 

 tubing C, to a reservoir E, which is filled with 

 water, and which can easily be raised or low- 

 ered by sliding the clamp K along S. On 

 the surface of the water in the burette there 

 is a small column of carbon bisulphide W, 

 which obviously, can be made to assume any 

 desired position in the burette by either 

 raising or lowering R, and then turning the 

 stop-cock n very gently. 



In my first experiments I used mercury ^ _ 

 in place of water in R, and water in place of 

 carbon bisulphide as a movable index. But 

 this combination was unsatisfactory; I found 

 it exceedingly difficult to read the level I, 

 both on account of the convexity of the mer- 

 cury surface, and also on account of the 

 peculiarly disturbing light reflexion from the 

 bounding water-mercury surface. 



The combination, water and carbon bisul- 

 phide works admirably if the following precautions be taken. 



The burette must be ihoroughly cleaned from grease and dust 

 before calibration. The resevoir R is then filled with freshly 

 distilled water, and matters are so arranged that the level of the 

 water stands at g, the loiccsf graduation of the burette. A long 

 thistle funnel is then inserted into the burette, and a small 

 quantity (say 5c. c. ) of recently distilled CS-. is poured gently on 

 the surface of the water. Under these circumstances the CS., in 

 spite of its higher specific gravity, floats on the water, and 

 exhibits two easily localized concave meniscuses. It is well to 

 shake the CS. up with distilled water, so as to thoroughly satur- 



