Geology and Mineralogy. 



As one of the two coexistent phases is made to vary in a < 

 '■as maimer, the other may approach it and ultimately ( 

 with if. The phase in takes place i 



I Phase. 



I absolutely unstable phases is i 



limits of absolute stability, this process' cannot be indetinitely 



l, for before the substance can enter a new region of 



it must pass out of the region of relative stability into 



one of absolute instability, when it will at once break up 'into a 



system of stable phases. 



Thus in water for any given pressure there is a corresponding 

 temperature at which it is in equilibrium with its vapor, and 

 beyond which it cannot be raised when in contact with "any gas. 

 B»t if, as in the experiment of Dufour, a drop of water is carefully 

 freed from air and entirely surrounded l»y li.piid which has a high 

 boiling point, it may remain in the liquid state at a temperature 

 far above the boiling point corresponding to the pressure, tie. ugh 

 if it comes in contact with the smallest portion of any gas it 

 instantly explodes. 



But it is certain that if the temperature were raised high enough 



any other subst 



Water io;iv : 



ild then explode without requiring the c 



cooled below the temperature at which it 

 generally freezes, and if the water is surrounded by another liquid 

 of the same density the pressure may also be reduced below that 

 of the vapor of water at that temperature, it the water when in 

 r bi> phase is brought in contact with ice it will freeze, but if 

 brought in contact with a gas it will evaporate. 



Professor Guthru has reo ith disco\ red i von rei . kabh- 

 C; >se "f equilibrium of a liquid which niitv be solidified in three 

 different wavs bv contact with three different sub stances. This 

 ^a snlutiouofcl'derideotcahdum in water containing 37 percent 

 " j f bi Bait. This solution is . : ' -37 C, 



When it forms t lie -olid < r\ hvdratc having the >ai < i dtion 

 as itself. But it mavbeccoled - rature. 



«'""1 Mien if it is touched With a bit of ice it throws up ice. if it IS 

 iri, the anhvdrous salt it throws down. anhydrous salt, 

 •>...! ^ :i :. , , -. •.. .1 , i,_. !.... + . :«- 



II. Geology and Mineralogy. 

 1- The Zoess of the Rhine and Danube, by Thomas ISttt. 

 F.G.S.— Mr. licit discusses the characters, j 

 the loess, and the evidences in tl 



and organic remains it contains in some places, of its haying 

 originated in connection with the Glacial era, observing that ' no 



