322 APPENDIX 3 



water. Leave overnight at room-temperature (or for several hours 

 at 37° C); then add 120 ml of buffer solution A. Heat over double 

 asbestos gauze, with occasional shaking, until the fluid boils. Fix 

 the large U-tube in a perfectly vertical position. Allow the fluid to 

 cool to about 48° C and then pour some of it into the U-tube. 

 Allow the agar to set. Mark the height of the agar with labels. 



For the two small U -tubes (agar bridges). Put 0-5 g of agar in 

 100 ml of distilled water. Leave overnight at room temperature (or 

 for several hours at 37^ C). Heat over double asbestos gauze, with 

 occasional shaking, until the fluid boils; add 10 g of sodium 

 chloride; shake. Fix the small U-tubes in a vertical position. 

 Allow the fluid to cool to about 48° C and then pour some of it into 

 the U-tubes so as to fill them to the brim. Allow the agar to set. 



Put copper sulphate solution, 10% aqueous, in the small beakers. 



Dissolve the dye at 0-2% in distilled water. Before the experi- 

 ment starts mix this solution with an equal volume of buffer 

 solution A (p. 321). Methylene green is particularly suitable 

 because its cataphoretic movement is rapid. 



The only difficulty in the experiment is that the agar in the 

 large U-tube sometimes comes unstuck from the glass, and the 

 dye solution then slips down in between. The glass must be per- 

 fectly clean and the dye must be added very gently with a pipette 

 above the agar on both sides of the large U-tube. Add a little 

 alternately to each side. 



The water in the agar gel in the large U-tube moves slowly 

 towards the negative pole by electro-endosmosis. The columns of 

 dye solution above the agar on the two sides must be kept level by 

 occasional transference from one side to the other. 



Diffusion of dyes 



Prepare 'buffer solution A' according to the instructions given 

 under the heading 'Electrophoresis of dyes' (p. 321). The buffer is 

 at pH 7*1. 



Put I g of agar in 100 ml of distilled water. Leave overnight at 

 room-temperature (or for several hours at 37° C); then add 100 ml 

 of bufi^er solution A. Heat over double asbestos gauze, with occa- 

 sional shaking, until the fluid boils. Arrange several fairly long, 

 narrow test-tubes in a rack. Allow the agar solution to cool to 

 about 48° C and then pour some of it into the test-tubes so as to 

 fill them to within about 4 cm from the top. Allow the agar to set. 

 Mark the height of the agar with labels. 



