Abstract
The results obtained from experiments on the mechanical properties of single crystals of ice doped with several impurities are presented. At −70°C, small amounts of dissolved hydrogen flouride (HF) have a pronounced softening effect, ammonia (NH3) produces a slight hardening, and ammonium fluoride (NH4F) has no apparent effect. These results are discussed in terms of Glen's (1968) theory of dislocation movement in ice crystals and a possible explanation of the results is offered.