Seeking to systemalically identify and organize the physical and chemical properties of biomass particles for combustion in furnaces, an attempt is made here to theoretically describe the temporal change in mass of a burning particle of an organic solid. The development involves a series of simple models to highlight the mechanisms involved, the physical and chemical properties of concern and the expected results. Although many simplifying assumptions are made, the properties identified, the parameters which evolved and the final functional form of the results are expected to becorrect.