Barns — Thermodynamic Relations of Hydrated Glass. 3 



Again, during the intermediate stage, water-glass is non-resi- 

 lient : yielding remarkably to increase of pressure, it refuses to 

 expand when pressure is removed. The last stage is again 

 elastic but relatively incompressible. 



The extreme compressibility of water-glass during the stated 

 intermediate stage deserves especial comment. Beginning 

 with igneous glass and water* with compressibilities of the 

 order of 3/10 6 and 100/10 6 respectively at 210°, values are 

 reached in water-glass which exceed 500/10 6 . One may even 

 compare this result with so volatile a body as ether at different 

 temperatures and between 100 and 200 atm., as follows: 



Temperature = 29° 65° 100° 185° 



£X 10 6 = 156 207 305 741 



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

 body quite resembling igneous glass. 



5. Made in quantities in a large digester, water-glass is 

 obtained as a nearly homogeneous compact body, adhering forci- 

 bly to the walls of the retort, from which it must be removed 

 with wedge and hammer. A small lump held above a candle 

 flame soon fuses with loss of water to a milk-white pumice. 

 Left without interference in the cold for several weeks or 

 months, it spontaneously cracks and crumbles, eventually 

 becoming a loose mass breakable in the fingers, while the 

 original lump could be broken only with a hammer. In the 

 cold, therefore, phase 2 is unstable and passes back spontan- 

 eously into phase 1. Water is set free, probably under great 

 pressure, and hence the gradual crumbling of the mass. When 

 compared with the disintegration of minerals, we have here an 

 example of an enormously rapid chemical reaction, in solids. 

 The breakage of capillary tubes in the lapse of time instanced 

 above, § 2, is thus explained. 



*The rapidity with which, water attacks glass vessels at 210° makes it impossi- 

 ble to obtain more than an estimate of its compressibility. See my earlier 

 paper. 



Brown University, Providence, R. I. 



