Water in Hot Glass, 471 



(r/V) for tube No. 4 gave the following interpolated mean 

 values : — 



Thread-length (210°).... 16-0 14-5 13-6 12-0 cm. 

 /3xl0 6 260 350 440 70 



The final datum marks the subsidence of the whole phe- 

 nomenon, the /3 being nearly the normal datum for water 

 (the usual case of colloids, which retain the compressibility 

 of the solvent), and further volume decrement vanishing. 

 During contraction the mean rate of /3 change is 80 X 10 ~ 6 per 

 linear cm. of contraction. Since the initial cold length was 

 15*5 cm., this amounts to about 12 X 10 -6 for each per cent. 

 of volume decrease relative to the cold volume. This result 

 agrees fairly well with the data for tubes 1 and 2, 



6. The experiments with the next tube, No. 5, were in the 

 main a corroboration of the results for tube No. 4. The bore 

 was chosen larger. 



Temperature of Vapour-bath, 210°. 



Internal diameter (cm.). 



Section. 





Original -033 



•00085 



Cold thread-length 

 14'05 cm. at 20°. 



Corroded -057 



•00260 



External diameter, 

 •65 cm. 



The chart shows the march of volume and of compressibility 

 in the lapse of time. As a whole the reaction is slower than 

 in § 5 ; the thread is shortened by contraction at 210° to its 

 length for the cold tube in about 40 minutes, twice as long an 

 interval as before. 



Boiling began at 10 h 25 m , and constant temperature was 

 reached about 15 minutes later. The observations as a whole 

 are the same as in the preceding case. At ll h 15 m the silicate 

 failed to retreat with the advanced mercury column on 

 removing pressure. A peculiar result was observed, as the 

 mercury here ran down several centims., leaving the water- 

 glass full of oval cavities, and afterwards ascended of its own 

 accord to fill them again without manual interference at the 

 force-pump. 



I presume that pressure was reduced below the vapour- 

 pressure of the water absorbed in glass ; that the temperature 

 of the oil in the force-pump was thermodynamically reduced 

 by expansion of the oil ; that the latter gradually regained its 

 temperature, 0, by conduction, increasing the pressure in the 

 hermetically sealed barrel. Since d0/dp = av6/Jcp, a liquid of 

 low specific heat cp, low density 1/v, and large thermal expan- 

 sion a, contributes to this result. 



2K2 



