Knudsen effusion mass spectrometry (KEMS) is a valuable and versatile tool in physical chemistry, materials science, and geology. Most of the applications center on thermodynamic measurements. In this paper two novel applications of KEMS are discussed. The first is the determination of K isotope ratios for application to K-Ar dating. The second is the determination of silica thermodynamic activities in silicates via a reducing agent to increase signals without changing the condensed phase composition. This also involves the measurement of vaporization coefficient via a multi-cell KEMS method.