Limits to the concept of solid-state stability.

Recently published data about the decomposition of propantheline bromide in the presence of moisture resulted in a general, two-variable, phenomological equation relating the decomposition to the relative humidity and temperature. The true curve, however, is biphasic, since complete liquefaction occurs at some time point. This article deals with the development of a theoretical equation relating decomposition time, temperature, and relative humidity during the solid-state stage (i.e., during the period when solid is still present in the system).