We describe detailed studies of the interaction of HCl and HOCl with 60 wt % liquid sulfuric acid at 251-276 K as an example of research aimed at understanding the heterogeneous chemistry of the stratosphere. The theory of gas/particle kinetics coupled with measurements of the uptake of HCl and HOCl by bulk and particulate 60 wt % sulfuric acid yield the solubilities of HCl and HOCl, the HCl and HOCl mass accommodation coefficients, the HCl + HOCl liquid-phase rate coefficient, and the HOCl liquid-phase diffusion coefficient. These results are in very good agreement with theoretical predictions and extrapolations of other independent results.