532 Decomposition of Glass by Carbon Dioxide, 



the temperature to which the glass was heated was sufficiently- 

 high to expel the whole of the carbon dioxide, then we can 

 only account for 165*2 cubic centim. of carbon dioxide instead 

 of 236*9 cubic centim. There must therefore, even under the 

 most unfavourable conditions, have been at least 71*7 cubic 

 centim. of carbon dioxide fixed on the glass otherwise than 

 by chemical union. We cannot unfortunately determine how 

 much, however, actually was due to the decomposition of the 

 glass and how much to the capillary absorption. If, then, 

 carbon dioxide, under the conditions described, can overcome 

 the affinity of silica for soda, a similar action, although in a 

 lesser degree, may be expected from pure water. 



That such an action really does take place may be expected, 

 if one may draw a conclusion from the action at higher tem- 

 peratures, as indicated by the following fact, which I had 

 occasion to observe in the preliminary experiments on the esti- 

 mation of the tension of water- vapour at very high temperatures. 

 In these experiments I made use of narrow thick-walled tubes, 

 sealed at the upper end, and attached at the lower end to a 

 calibrated capillary tube 2 metres long, and which would 

 withstand a pressure of 600 to 800 atmospheres. In the 

 wider part of the tube containing air there was, standing over 

 the mercury column by which the approximate pressure was 

 measured, a column of water, and this was heated to 550° C. 

 in the thermostat described *. 



At the part of the wall of the tube with which the water 

 had been in contact there were alterations of a marked 

 character. 



The glass was transformed to more than a third of its 

 thickness into a hard white porcelain-like mass, and the inner 

 cavity of the tube diminished to one-tenth of its original 

 diameter. There can be no doubt therefore that glass and 

 other silicates intended to be used in the examination of such 

 questions are quite inapplicable. 



In order to obtain trustworthy results in absolute measure 

 without the interference of chemical influence, there remains 

 scarcely any other course than to repeat the whole of the 

 experiments on capillary absorption with very fine gold or 

 platinum wire, and allow for the chemical action on the 

 relatively small surface of the glass measuring-tube. 



* Bunsen, I. c. 



