Figure 6

Figure 6: Effect on Growth-Medium [NaCl] on E. coli Cellular Specific Gravity. Between 2x10⁴ to 1x10⁵ early log-phase E. coli cells grown in 0.5% lactose Luria Broth were "stopped" by making them to 7% NaBr (w/v) and centrifuged as per Fig. 1 for at least 50,000 g x minutes. Cell bands of approximately 1 mm thickness resulted. The specific gravity of the cells was obtained by refractometrically assaying the density of the liquid in which they were banded. Shown here are a combination of two sets of data (open and solid squares) each collected by students in different locations. One set was gathered from centrifuging at 3krpm for 20 min., and the other at 10Krpm for 5 min. The data sets are seen to mimic each other with good precision.