Allen and Clement — Bole of Water in Tremolite. 113 



therefore be about 1/1500 of an atmosphere or about 0*5 mm of 

 mercury. As it appeared that the loss of water under these 

 conditions goes on indefinitely, a new series of experiments 

 was made in which the mineral was heated in air which had 

 been bubbled through 65 per cent (by weight) sulphuric acid 

 having a vapor pressure at 25°, about the room temperature, 

 of 3 mm . The results follow : 



Time of 

 heating 



6 hours 



U " 



7 a 



It will be seen that the average loss is practically the same 

 as before. At this point, a small portion of material was 

 removed from the crucible and examined microscopically. No 

 essential change had taken place in its optical properties. 



The remainder was now ground line enough to pass a screen 

 containing 150 meshes to the linear inch, and a new charge of 

 1*6128 grams was taken. This was heated at 820° in an atmos- 

 phere saturated with water vapor, which at the temperature of 

 the room should have a partial pressure of about 23 mm . The 

 following are the results : 



Table 



VI. 









jmpera- 





Total loss 



Loss 



per day 



ture 





in mg, 



in 



mg. 



600° 





12-8 





•8 



n 





12*5 



— 



•3 



a 





13-3 





•8 



a 





13-7 





•4 





Table VII. 







Time of 



Tempera- 



Loss 



Loss per day 



heating 



ture 



in mg. 



in mg. 



5^- hours 



820° 



13-9 



13-9 



H " 



a 



17-5 



3-6 



6 



u 



18-4 



0'9 



6i " 



a 



19*4 



1-0 



6* " 



u 



19-6 



0-2 



6* " 



a 



19-7 



o-i 



At this stage, the mineral having lost altogether 2*05 per 

 cent of water, or 50 per cent of the total quantity, another 

 portion was removed and examined microscopically. It still 

 remained kupfferite, though a secondary change had taken 

 place, due probably to the oxidation of the manganese. The 

 color had become dull green, and dark brown patches, partially 

 transparent, were visible on some crystals. This secondary 

 change made further experiments useless. The material was 

 probably absorbing oxygen, in which case the total loss would 

 not represent all the water which escaped. The homogeneity 

 of the substance is preserved then during the earlier stages of 

 dehydration at least, though the experiments did not prove 

 that the loss of water was continuous. If this were the case, 

 however, and the water in kupfferite were dissolved, we can 



