418 



Scientific Proceedings, Royal Dublin Society. 



this department by Carl Hersch, 1 and it is to be regretted that his 

 death, immediately after the completion of the experiments, pre- 

 vented a continuation of his labours. His experiments and 

 analyses were conducted upon material which was. previously 

 dried with air. This is a point of considerable importance. If it 



be remembered that Si — OH loses its water at 100° C, it will 



^OH 

 be seen that hydrated silicates — if the H 2 is combined with the 

 Si0 2 , which in most cases cannot be otherwise — must lose a portion 

 of their water at this temperature. Hence the analysis would no 

 longer give the exact constitution of the mineral, if the powder 

 were previously dried at a temperature of 100°. 



At 100°, H 2 Si0 3 commences to lose its water. Al 2 (OH) c , 

 (or A1 2 3 .3H 2 0), which occurs in nature as a monoclinic crystal- 

 lizing mineral, Hydrargillite, loses, according to Mitscherlich, 2 two 

 molecules of H 2 at a temperature a few degrees over 280°, and then 

 passes into the rhombic Diaspore A1 2 3 .H 2 0. The latter remains 

 unaltered at 450°, the remaining molecule being expelled only after 

 lengthy ignition. Therefore, when the water is expelled from alu- 

 minous silicates at a temperature under 280° C, Hersch concludes 

 it is combined with the silicium, and not with the aluminium. 

 His experiments upon natrolite and scolezite are as follows : — 



1 Der Wassergehalt der Zeolithe. Zurich : 1887. 



2 Fortsetzung der Beitrage zur analyt. Chemie — Untersuchung des Alaunsteines, 

 &c. Journal fur praktische Chemie. Bd. 83, p. 468. 



3 From Jakuben in Bohemia, Hersch, 1. c, p. 34. 



4 From' Bulandstindr in Iceland. 



