Indications that surface chemical resistance is influenced by absolute humidity at the time of forming and annealing led to a laboratory study in which bottles were held at temperatures in the annealing range and higher in atmosperhes of humidity ranging 0.0000 to 0.020lb H2O/lb of dry air. The top humidity is that of air saturated at 77 deg F. After cooling to room temperature, chemical resistance was measured by filling the bottles with pure water, autoclaving at 121 dec C for one hour and titrating the alkaline matter dissolved. On exposure to moist air at temperatures in or above the annealing range, the chemical resistance of ordinary bottles does not change much. In dry air, the resistance increases until extracted alkali is reduced to less than 0.1 of the original value.
