of Glass by Carbon Dioxide. 531 



076 metre pressure takes up about 0*2 per cent, of its 

 weight of carbon dioxide behaves quite differently in capillary- 

 films, for it is not then under a pressure of one atmosphere, 

 but under a very high capillary pressure, and so can take up 

 so much more carbon dioxide, that, if we would study the 

 decomposing action of the solution, we have no ground of 

 comparison, and must solve the problem by direct experiment. 



Such an experiment could not be carried out either before 

 or during the previous experiments without destroying the 

 capillary glass thread ; and thus it was not possible to proceed 

 with the examination of this question till the experiments 

 already proceeding were finished. 



The 49*453 grins, of glass used were, for this purpose, 

 removed from the measuring tube and extracted with cold 

 distilled water of such a purity that it left only 5 o^ooo- son( ^ 

 residue on evaporation. For the extraction, portions of 300 

 grammes of water were taken, and the whole 3000 grammes 

 so used were filtered through a double filter and evaporated 

 to dryness in a platinum vessel. The residue dissolved in 

 hydrochloric acid with evolution of carbon dioxide, and con- 

 tained 0*8645 grm. of sodium chloride and 0*0608 grm. of 

 silica along with unweighable traces of calcium chloride or 

 pofassium chloride. 



From the composition of the capillary threads *, it appears 

 therefore that there was not less than 2*882 grms. of the 

 glass decomposed, or 5*83 per cent, of the whole quantity 

 used. We see, then, that the chemical action of carbon dioxide 

 under the influence of pressure in capillary films is far greater 

 than we had any cause to expect. The carbon dioxide had, 

 in the course of the experiments, taken up from the glass a 

 quantity of soda corresponding to 0*7841 grm. sodium car- 

 bonate, and containing 0*325 grm. carbon dioxide. 



Since sodium carbonate is not decomposed, even at very 

 high temperatures, the 236*9 cubic centim. or 0*4659 grm. of 

 carbon dioxide set free on heating could not arise from this 

 decomposition product of the glass thread. But sodium car- 

 bonate takes up carbon dioxide and is transformed into the 

 bicarbonate, and this carbon dioxide is set free again on heating, 

 exactly in the same manner as in these observations. 



It is thus to be determined whether the phenomena ob- 

 served in capillary absorption can be exclusively attributed to 

 the formation of sodium carbonate. 



If we start from the most unfavourable supposition that all 

 the sodium carbonate formed became bicarbonate, and that 



* Wied. Ann. xx. p. 545 (1883) [Phil. Mag. March 1884]. 



