MICROLITER BURETTES 



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covered by a layer of paraffin oil. This serves to protect the tip, 

 and if the protecting tube and the tip are sealed together by a rubber 

 connection, siphoning-over of the solution is prevented. By adjusting 

 C so that only a small positive pressure is applied, the surface 

 tension at the fine tip will prevent liquid from escaping, and delivery 

 will occur only when the tip is immersed in the solution to be titrated. 

 This, of course, is the principle used for the other microburettes 

 that have been described. Stock bottles can be interchanged without 

 affecting the capillary in any way. One of the instruments that 

 Heatley constructed had a capacity of 0.1 ml. over a 25 cm. scale, 

 and the capillary was divided in 1.0 [x\. graduations. The relatively 

 large volume of the stock bottle and the air space between the 

 mercury in the leveling bulb and that in the capillary would make 

 this burette particularly prone to errors arising from temperature 

 fluctuations during titration. 



Fig. 89. Micrometer burette. 

 From Scholander, Edwards, and Irving (1943) 



Boell Burette. One of the easiest burettes to construct is that 

 of Boell (1945). The instrument consists of a horizontal calibrated 

 capillary tube drawn out to a fine delivery tip at one end, bent 

 vertically and pointing downward; the other end of the capillary is 



