MICROLITER BURETTES 263 



delivered amounts with an accuracy of about 0.02 fA. The burettes 

 are commercially available from Emil Greiner Co. and from 0. 

 Hebel, Edward Martin Biological Laboratory, Swarthmore College. 

 Loscalzo and Benedetti-Pichler Burette. Loscalzo and Bene- 

 detti-Pichler (1945) described the titration of microgram samples 

 in volumes of 0.05-0.50 fil. using a burette (Fig. 90) consisting of 



TP ST TR ^^Li n 



Ref. 



HW 



^ T 



L V_ 



SH 



STB 



TV 



TP 



MS 



H 



Fig. 90. Titration of microgram samples. Upper drawing shows burette with 

 remote control, 7X natural size. Center drawing shows open titration cone, 

 7X natural size. At bottom, burette, schematic: TP, tipi; ST, shaft; TR, taper; 

 SK, shank; Ref., reference mark; SH, shank of titration cone; TV, titration 

 cone proper; STB, shaft of burette; HW, meniscus of hydraulic water; MS, 

 of standard solution; A. air column; H, pipette holder of metal with rubber 

 washer (horizontal shading. From Loscalzo and Benedetti-Pichler (1945) 



a piece of capillary tubing drawn out to a fine tip. The titrations are 

 carried out in a moist chamber on the stage of a low-power micro- 

 scope and the operations are controlled by a micro manipulator. 

 Measurements of the quantity of the solution delivered from the 

 burette are made by observing the displacements of the meniscus 

 on the scale of an eyepiece micrometer used with the microscope. 

 The solution is moved by the pressure transmitted from a leveling- 

 bulb arrangement (Fig. 91). The method of handling the small 

 volumes of liquid was developed by Benedetti-Pichler (1937) for 

 micro qualitative analysis, and it was expanded later by Benedetti- 

 Pichler and Rachele (1940), and Benedetti-Pichler and Cefola 

 ( 1942) . Details of the apparatus and manipulations will not be given 

 since there have been no histochemical applications of titrations in 

 volumes of 0.05-0.50 /i.1. However, the possibilities in this respect are 

 somewhat intriguing. 



