Under what conditions will the gauge pressure of a cylinder of N2O accurately represent its con-tents?

1. When the liquid in the cylinder has completely vaporized
2. When the ambient temperature exceeds the critical temperature
3. When the filling density is less than 1.0 (water-filled)
a. 1 and 2 only
b. 1 and 3 only
c. 2 only
d. 1, 2, and 3

ANS: C
Should a cylinder of nitrous oxide warm to 97.5° F (its critical temperature), all the contents would convert to gas. Only at this temperature and above does the cylinder gauge pressure accu-rately reflect cylinder contents.