Water in Hot Glass. 



475 



ing table contains the results, taking Everett's data (Tables) 

 for k and n : — 



Tube No 



1. 



2. 



3. 



4. 



5. 



6. 



4-2 

 4-4 





Original bore dft X 10 G - 



Corroded bore £/3xlO G = 



4-2 

 4-3 



4-2 

 4-3 



42 

 4-2 



42 

 43 



42 

 4-2 



Thus the mean effect of the enlargement of bore, due to 

 internal corrosion, is at ordinary temperatures but '000 0001 

 in the extreme case, or only a few tenths per cent, of the 

 value of ft for cold water. As an explanation of the changes 

 of ft obtained, which run as high as 600 per cent., the elastic 

 discrepancy is thus out of the question *. 



The effect on the volume-contraction, being Sft.p, would 

 be in like degree negligible. 



Finally 3 according to Amagat f the increase of compressi- 

 bility of ordinary glass between 0° and 200° C. is about 

 5*9 per cent. Hence even at 200° the elastic discrepancy 

 will be in almost the same degree negligible as at ordinary 

 temperatures. 



In experiments like the above, tubes which initially with- 

 stood 400 or 500 atmospheres, after prolonged straining will 

 break even at 100 atm. or less. This result is rather to be 

 ascribed to the fatigue of elasticity or to molecular strains 

 imparted during cooling ; for it is not unusual when corrosion 

 is altogether absent. 



9. The next point at issue relates to the viscosity of glass 

 at 200°. In a tube subject to viscous deformation the current 

 towards the top may be regarded as the result of viscous 

 stretching due to internal pressure. Increased ft then 

 represents the initially increased viscous yield accompanying 

 the increased stress, the yield vanishing asymptotically in 

 the lapse of time. 



Reasons against this assumption are again of a quantitative 

 kind. When the elastic deformations are not of serious 

 consequence, the viscous changes are apt to be less so. 

 Moreover viscous phenomena would not vanish in one hour 

 as fully as the curves for tubes 4, 5, and 6 indicate. Finally, 

 in a very large number of experiments in which hydrocarbons 



* For experiments in a like direction, see my paper in Am. Journal, 

 (3) xxxix. p. 485 (1890). 

 f Notices sur les Travaux Sc. de M. E.-H. Amayat, Paris, 1896, p. 36. 



