Study of natural glasses through their behaviour as membrane electrodes

THE low-temperature chemical alteration of natural glass occurs in two stages: an initial stage in which it remains glassy but absorbs as much as 6 per cent water¹, and a final stage in which devitrification to clay minerals, with release of silica, occurs^2,3. During the first stage the composition of the glass may change, with gain of K₂O and water and loss of Na₂O (Smith, R. L., personal communication). This change is due to ion exchange.