NEW FLUIDS IN MINERALS. 339 



plate, it ceases to reflect light like the thinnest 

 part of the soap-bubble; and when it is again 

 accumulated into a thicker drop, it is covered 

 with thin coloured rings of thin plates. 



After performing these motions, which some- 

 times last for ten minutes, the fluid suddenly 

 disappears, and leaves behind it a sort of granular 

 residue. When examining this with a single 

 microscope, it again started into a fluid state, and 

 extended and contracted itself as before. This 

 was owing to the humidity of the hand which 

 held the microscope, and I have been able to 

 restore by moisture the fluidity of these grains 

 twenty days after they were formed from the 

 fluid. This portion was shown to the Rev. Dr. 

 Fleming, who remarked, that, had he observed 

 it accidentally, he would have ascribed its appa- 

 rent vitality to the movements of some of the 

 animals of the genus Planaria. 



After the cavity has remained open for a day 

 or two, the dense fluid comes out and quickly 

 hardens into a transparent and yellowish resin- 

 ous-looking substance, which absorbs moisture, 

 though with less avidity than the other. It is 

 not volatilized by heat, and is insoluble in water 

 and alcohol. It readily dissolves, however, with 

 effervescence in the sulphuric, nitric, and mu- 

 riatic acids. The residue of the expansible fluid 

 is volatilized by heat, and is dissolved, but with- 

 out effervescence, in the above-mentioned acids. 

 The refractive power of the dense fluid is about 

 1.295, and of the expansible one 1.131. 



The particles of the dense fluid have a very 

 powerful attraction for each other and for the 

 mineral which contains them, while those of the 

 z 2 



