106 



Dr. C. Barus on the 



of the observation counting from the beginning of ebul- 

 lition in the vapour-bath ; v the total increment of volume 

 due to the thermal expansion, V the total volume, so that 

 v/Y is the mean expansion per uuit of volume at 185° ; /3 the 

 mean compressibility within 300 atmospheres. 



Table showing Thermal Expansion and Compressibility of 

 Silicated Water at 185° and 20 to 300 atmospheres. 

 Diameter of tube '045 centim. Length of column of 

 water at 24°, 14 centim. 



e. 



v/V . 10 3 . 



(3 . 10 G . 



t. 



e. 



v/V . 10 3 . 



/3.10 6 . 



t. 



°c. 







min. 



°c. 







mm. 



24 



±0 



44 





185 



4-44 



141 



40 



185 



+ 103 



77 



18 



185 



+ 27 



163 



45 



185 



86 



97 



25 



185 



+05 



184 



50 



185 



75 



112 



30 



185 



-15 



221 



55 



185 



60 



125 



35 



185 



-29 





60 



At the conclusion of the experiment the thread was solid, 

 as I supposed, at high pressure (300 atm.), though not 

 apparently so at low pressure. This was inferred since the 

 mercury thread advancing under pressure did not, on removal 

 of pressure, return again as a whole, but broke into small 

 parts in a way to make further measurement without 

 immediate value*. On breaking the tube apart after cooling, 

 and examining it under the microscope, the capillary canal 

 was found to be nearly, if not quite, filled with a white glassy 

 incrustation. This shows that the glass swells in marked 

 degree on hydration, whereas the combined volume of glass 

 and water put into action, simultaneously contracts. If the 

 values of v/Y given in the table be examined, it appears that 

 whereas the original volume increment per unit of volume is 

 greater than *103 for the rise of temperature from 24° to 185° 

 at 20 atmospheres, this increment has nearly vanished after 

 50 minutes of reaction. The thread at 185° is now only as 

 long as it was at 24°. After 60 minutes of reaction it is even 

 markedly shorter at 185° than at 24°, pressure remaining 

 constant throughout. 



At the same time the compressibility, /3, of the silicated 



* A succeeding paper will take up the research from this point 

 onward. 



