Pure Ho2Ti2O7 and Dy2Ti2O7 exhibit spin ice behaviour. The recent discovery of monopoles and "magnetricity" in Dy2Ti2O7 spin ice has only added to the interest in these materials. In a recent experiment on MuSR (RB1110219) we observed evidence for magnetricity in Ho2Ti2O7. Our data also suggest that the behaviour characteristic of the spin ice state is present in a Ho2-xYxTi2O7 sample with Y doping as high as x=1. In a continuation experiment we propose to study four more samples of Ho2-xYxTi2O7, two with x close to zero, to study effects of doping on magnetricity, and two with x > 1.0 to complete our study of the effects of Y doping on the spin ice state. To ensure that only the highest quality materials are used the samples will all be single crystals. Experiments will be performed between 50 mK and 10 K.