260 



TITRIMETRIC METHODS 



graduations on the tube itself. The burette has a total capacity of 

 about 0.1 ml. and is capable of a precision in reading of ±0.03 /tl. 

 (Sisco, Cunningham, and Kirk, 1941). (Available from Micro- 

 chemical Specialties Co.) 



Heatley Burette. The essential differences between the Heatley 

 ( 1935) burette and the preceding models are that the mercury 

 displacement is effected by means of a leveling bulb rather than a 

 screw, the standard solution is in contact with paraffin oil, and 

 delivery is made directly from a stock bottle of the solution. A 

 diagram of the instrument is shown in Figure 88. The tube leading 



100 B 



I I I I I I— I I I I I 



TIT 



Fig. 88. Burette. 

 From Heatley (1935) 



from the delivery tip extends to the bottom of the stock bottle which 

 has a 2 oz. capacity and is lined with paraffin. The stopper of the 

 stock bottle is a cork infiltrated with paraffin, and the 5 mm. vertical 

 tube H ends flush with the bottom of the cork. The upper part of H, 

 the capillary connection {M) , the three-way stopcock {E), reservoir 

 (F), and the space (D) are all filled with paraffin oil. The space 

 under D and part of the capillary tube {B) contain mercury. The 

 leveling bulb arrangement (C), by which the pressure is regulated, 

 also contains mercury. An air space exists between the leveling 

 bulbs and the mercury thread in the capillary. No air is permitted 

 between the mercury under D and the delivery tip. Interchangeable 

 delivery tips fitted through a ground-glass joint may be used. When 

 not in use, the tip is dipped into a tube of the titration solution 



