440 



on the reproduction, l>y the stronii' radiation of the phosphorescent 

 screen and the enlargement of tlie central spot caused hy it, l)ut 

 they were distinct on the original i)hotographs. 



It is therefore doubtless, that these photographs can be considered 

 to have brought the proof of the fact, that the pseudotetragonal c-axis 

 of the apophyllite-crystals, is not even a binary axis ; but that at 

 best it can be compared with the vertical axis of a monosi/minetric 

 molecular ari-angement : the original molecular structure of apopkyUite 

 is not of tetragonal, but of iiionoclinic symmetry. 



We once more emphasize in this connection the existence of the 

 group of five intensive spots, just beneath the centre of the image. 

 Indeed this garland of live spots, which correspond to five molecular 

 planes, seems to be typical for all apophyllites of American origin ; 

 it plays evidently in these silicates a preponderant role. As in 

 literature there can be found some data, relating to the fact, that 

 a heating to 270° C. would be able to expel a part of the water 

 and to make the crystal tetragonal in realifij, — we have studied 

 the etfect of such a heating at 270° to 3(W C. by means of the 

 heating-appai-atus formerly described by us. And now it was found, 

 that all spots disappear, but that the mentioned five intense spots 

 are elongated like the fingers of a hand (tig. 3/; on plate II). This 

 fact could be explained by the supposition that the original sets of 

 parallel molecular planes, l)y which the five intensive spots were 

 produced, are changed during the desliydratation and heating gradually 

 into tlie same number of now divergent molecular planes lying in 

 live zones respectively. This would be possible, if the molecular 

 planes, which are situated nearer to the crystal-surface, will lose 

 their watermolecules sooner and more easily than those situated 

 nearer the inner part of the crystal : the expelling of the water 

 takes place namely very slowly and gradually, while the planes are 

 rotating round their zone-axes continually during this deshydratalion. 

 It is possible, that an analogous, but far more irregular distortion 

 of the positions of the molecular planes will be the cause of a gra- 

 dually getting vaguer and finally of a disappearing of all other points 

 and spots; if not the other explanation, namely that all these [)oints 

 correspond to the action of the 2üatermo\ecu\es alone, can be accepted. 

 It will be only possible to give some stronger aftirmation of this view, 

 if more zeolithic silicate will be investigated in an analogous way. 

 The tig. 'Mj is made, after the heated crystal being cooled down 

 to the roomtemperature ; it a[\\)ei\vs to \)e completely identical however 

 with the image obtained at 300° C. within the furnace, and it is 

 only reproduced here instead of the other, because the last mentioned 



