630 



STABILITY OF BACTERIAL SUSPENSIONS. 



cell. This flattened end is ground smooth and is cemented to the end 

 of the cell. The same process is repeated at the other end of the 

 cell. The method of arranging the electrodes is apparent from the 

 figure. The best material for cementing the cell together was found 

 to be soft "De Khotinsky cement." The pieces of glass are warmed 

 to about 80° in an air bath, coated with a thin layer of cement and 

 pressed together. The surplus cement is then removed with wire 

 and the last traces are wiped off with a piece of paper moistened with 

 toluene. After the end-pieces have been fastened to the cell it is 



3.way 

 ^WJ 5top.cocK 



Zn electrode 



Class btoch -^ \N Supporting stnp 0.8 mm 

 ^Cwec^lass 0.5 mm. 



Fig. 1. 



advisable to run more cement around the joint to strengthen it; this 

 can easily be done by using a small soldering iron, the cement being 

 handled in the same way as solder. 



Calibration of the Cell— It is necessary to know the drop in potential 

 per cm. in the cell itself. Since the area of the connecting tubes, etc. 

 in general is different from that of the cell it is necessary to correct 

 for this difference. If the apparatus as a whole is filled with the same 

 solution, as is the case during an experiment, the total resistance of the 

 solution will evidently be proportional to the length and inversely 

 proportional to the cross-section. Since the drop in potential per cm. 



