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DAVID R. BRIGGS 



3. Choice of Apparatus 



Microelectrophoresis apparatus with observation cells of the 

 cylindrical type (8) have the advantage of being simplest to construct. 

 A simple capillary tube of 0.5 to 1.0 mm. bore, with an area ground 

 and polished flat at the point where observation with the microscope 

 is to be made, can be sealed to electrode chambers and to inlet and 

 outlet tubes to complete the construction of the apparatus. The dif- 

 ficulty of focusing at the proper depth for observation, however, seri- 

 ously limits the accuracy of results obtained with the cylindrical 

 cell. A cylindrical cell {9) that employs two capillary tubes bearing 

 definite ratios to each other both as to radius and length offers some 

 improvement with regard to this criticism of cylindrical cells gener- 

 ally. In this instrument back-flow of fluid resulting from electros- 

 motic displacement along the walls of the tubes is taken care of to 



Fig. 1. Flat horizontal microelectrophoresis cell of 

 Abramson and Moyer (2). 



such an extent by the larger capillary (not the one in which observa- 

 tions are made) that there exists a static condition of the fluid in the 

 center of the observation tube. Under these conditions velocity 

 measurements of particles made in the center of the small tube will 

 be due to electrophoretic movement alone. The greater increment 

 of cell depth at which focus will be approximately correct allows for a 

 higher probability of accuracy of measurement with this cell than is 

 the case with a simple cylindrical cell. 



"V\Tiile these and a number of other cells {10-13) have been used 

 more or less successfully over the period of the last few decades, the 

 flat cell instruments illustrated in Figures 1 and 2 have, in the experi- 

 ence of the writer and of many others who have used them, proved 

 most amenable to routine laboratory use and approach most closely 



