///. TITRIMETRIC TECHNIQUES 



A. MICROLITER BURETTES 



The microliter burettes employed in histochemical procedures 

 fall into two general groups. In one a capillary glass tube is 

 calibrated so that the volume of liquid delivered can be determined 

 by observing the position of a meniscus. These burettes are usually 

 modifications of the Brandt-Rehberg (1925) instrument, which is 

 arranged to move the column of solution by the pressure of a 

 mercury thread controlled by a screw. Mercury in a reservoir is 

 displaced by turning in the screw and the displaced mercury moves 

 into the glass capillary. Instruments of this general type have been 

 described by Pincussen ( 1927) , Linderstr0m-Lang and Holter 

 (1931, 1933a), Kirk (1933), Sisco, Cunningham, and Kirk (1941), 

 Links (1934), and Boell (1945). In the Heatley (1935, 1939) 

 microburettes the pressure is supplied by leveling-bulb arrange- 

 ments, and both Conway (1934) and Hawes and Skavinski (1942) 

 employ hydrostatic pressure in their instruments. The Conway 

 burette was modified by Ramsay ( 1944) for use under anaerobic 

 conditions (page 279). 



In the other general group of burettes a calibrated capillary tube is 

 not used, but the screw, usually in the form of a micrometer, is cali- 

 brated instead. These are essentially modifications of the instrument 

 described by Widmark and Orskov ( 1928) . Krogh and Keys ( 1931) , 

 Kirk (1933), and Krogh (1935) employed a fine screw to move the 

 plunger of a small glass syringe for the accurate delivery of small 

 volumes of liquid (page 174). Trevan (1925), Dean and Fetcher 

 (1942), and Hadfield (1942) used the spindle of a micrometer to 

 operate the plunger. Probably the best micrometer burette is that 

 designed by Scholander ( 1942) and later improved by Scholander, 

 Edwards, and Irving (1943). In this instrument the spindle of the 

 micrometer is used to displace the mercury in the reservoir. An 



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