Water in [lot Glass. 479 



the reaction (concentrated water-glass, subsidence of volume- 

 contraction) phase 2 is stable. Both cases correspond to 

 steep isotherms. Toward the middle region of the reaction 

 (maxima of compressibility) phases 1 and 2 are mutually 

 stable in presence of each other. Hence the horizontal iso- 

 therms corresponding to the critical region are cut through 

 in a march from greater to smaller corresponding tempe- 

 ratures. 



That phase 2 is really unstable during the first stage of 

 reaction is shown by the approximate constancy of the values 

 of compressibility throughout intervals of pressure as high as 

 could be applied. For instance at 185° : 



Pressure interval... 20 to 100, 



100 to 200, 



200 to 300, 



300 to 400 atm, 



10 6 x/3 = 146 



144 



142 



146, 



and fifteen minutes later, 









10 6 x/3 = 188 



176 



201 



189. 



Again, during the intermediate stage water-glass is without 

 volume elasticity; yielding remarkably to increase of pres- 

 sure, it refuses to expand when pressure is removed. The 

 last stage is again elastic, but relatively incompressible. 



The extreme compressibility, /3, of water-glass during the 

 intermediate stage stated deserves special comment. Be- 

 ginning with igneous glass and water with compressibilities 

 of (say) /3 = 3xl0- 6 and 100 x 10~ 6 respectively at 210°, 

 values of j3 are reached which exceed 500 x 10~ 6 . One may 

 even compare this result with so volatile a body as ethylic 

 ether * at different temperatures between 100 and 200 atm., 

 as follows : — 



Temp, of ether, 29° 65° 100° 185° 



/3 x 10 6 156 207 305 741. 



Yet the water-glass solidifies in the cold to a hard incom- 

 pressible colourless body, quite resembling igneous glass. 



Brown University, 

 Providence, R.I., U.S.A. 



* Am. Journal, (3) xxxix. p. 488 (1890). 



