Carbonic Acid in Mineral Cavities. By Walter N. Hartley. 175 



point, may be improved upon by placing the specimen in a glass 

 cell with parallel sides and immersing this in water of known tem- 

 perature ; on removing this for examination, the sides of the cell 

 may be wiped day without fear of the mineral losing an appreciable 

 amount of heat. Being now engaged in the study of other rocks 

 and minerals, details regarding these had better be left for another 

 communication. I have elsewhere shown* the nature of the chemi- 

 cal reaction which would most probably yield quartz crystals with 

 carbonic acid cavities, but this explanation could not be applied to 

 the formation of topaz and sapphire. 



* I 



Journal of the Chemical Society,' February 1876. 



