Experiments on titanium dioxide show that it is an electronic semi-conductor in which the the current carriers are actually free electrons, as contrasted with the hole conduction of the other type of semi-conductor. It is found that the variation with oxygen pressure is that which would be expected if the titanium dioxide decomposes in the following manner: TiO2-->Ti++O2+e-. The deviation of the curves at low pressures is probably due to the presence of small impurities in the samples used. It is found that the variation of conductivity with temperature is represented by the formula σ=Ae-∊kT. The activation energy ∊ is about 1.7 electron volts. Transport measurements show that the ionic conductivity is less than that which can be measured in these experiments. Measurements of the Hall effect, although not very quantitative, show that the mean free path for the conduction electrons is very small.