476 Br. Carl Barus on the Absorption of 



were subjected to much more intense pressures (400 atm.) 

 even at 310° in capillary tubes, I never noticed volumetric 

 evidence of viscous deformation comparable to the above. 

 Add to this the appearance of the tube ; i. e., the passage 

 from an opaque corroded interior gradually to a homo- 

 genous limpid jelly at the conclusion of the experiment, in 

 parallel with the observed volume changes subsiding in a clear 

 tube, and with the march of compressibility through 

 enormously accentuated values, terminating in the relatively 

 small values for hot water. Finally, after volume-contraction 

 censes (saturation) there is no further viscous response to any 

 pressure excess whatever. 



Viscosity is therefore not available to account for the volume- 

 contraction observed. To make quite sure a special experi- 

 ment was made with a thread of paraffin, 18*19 centim. long, 

 at 210° and about 100 atm. After more than an hour's 

 heating (observed 65 min.) the thread had gradually increased 

 in length to 18*23 centim., due no doubt to the gradually 

 rising temperature of the vapour-bath. The data given on 

 the chart (curve marked paraffin) show that there is no 

 relation between the present experiments and the behaviour 

 of water. 



10. I therefore regard it as established that the observed 

 volume-contractions are real. The endeavour may now be 

 made to compute limits for the density of the water-glass. 

 Two ways, suggest themselves : (1) By comparing the initial 

 volume of igneous glass and water with the final volume of 

 water-glass within the same bore (limit of corrosion) ; (2) By 

 making allowance for the advance of the thread of mercury 

 into the column of water-glass. 1 made these computations 

 for all the tubes ; but as the reactions in Nos. 1, 2, 3 are 

 incomplete, Nos. 4, 5, 6 only need be given. The first method 

 in these cases gave 3'4, 3*0, 3*5 respectively as the density 

 of solid water-glass. This is obviously a superior limit seeing 

 that the thread does not contract as a whole. The density 

 of the igneous glass is but 2 '46. The second method gave 

 me 2*40, 2'25, and 2*35 respectively as the densities of the 

 water-glass in the three cases. These data present an inferior 

 limit (since the thread of mercury widens in advancing 

 through viscous glass and since the full length of contraction 

 cannot be observed), just as the preceding data are a superior 

 limit. Hence the density of water-glass cannot differ yevy 

 much from the density of igneous glass (2*46) . Though the 

 two sets of data differ widely, one may estimate the volume- 

 contraction from their mean value to be about 20 per cent, 

 of the combined volume of igneous glass and water, for com- 

 plete subsidence of the reaction. 



