128 BELL SYSTEM TECHNICAL JOURNAL 



a Pyrex Glass which will be indicated in the experiment as number 7. 

 No analysis was made of this glass but it is known to be a boro-silicate 

 glass practically free from alkali and heavy metals. From the pres- 

 sures of the gases obtained, the distribution of gas evolution over the 

 various intervals was determined. Expressed in terms of percent- 

 age of the total gas evolved over the entire range, these results are 

 shown graphically in Fig. II. 



It will be noted first of all that these curves with the exception of 

 number 6, are in general similar to those obtained by Sherwood (loc. 

 cit.) in that they show both maximum and minimum points. Glass 

 No. 6 was found in this experiment as in the preceding one to behave 

 quite differently from numbers 3 and 4, although chemically it is very 

 similar. The explanation for this difference will appear later. The 

 curves show very clearly the distinction between the adsorbed and 

 absorbed gases. It is seen that the adsorbed gases for the lime and 

 lead glasses are practically all given up at a temperature of 200°C. 

 while 300 C. is required in the cases of the boro-silicate glasses. The 

 absorbed gases begin to come off at the softening points of the various 

 glasses; 400 C. for the lead and lime glasses and 600°C. for the boro- 

 silicate glasses. The steeper slopes of the curves 1 and 2 above 300°, 

 as compared to 3 and 4 are undoubtedly due to the fact that these 

 glasses (lime glasses) become fluid more rapidly than do the lead 

 glasses and therefore give up their dissolved gases at a more rapidly 

 increasing rate than do the others. In this connection it should be 

 stated that the amount of absorbed gases found in the above exper- 

 iments represent only that portion of the dissolved gases which lie 

 nearest the surface of the glass. Owing to the great viscosity of the 

 glass at the temperatures used, the rate of diffusion of the gas would 

 be altogether too slow to permit any considerable portion to reach 

 the surface. 



Some data that were taken in some of the experiments carried on 

 in the investigation of the adsorbed gases are interesting in that they 

 seem to throw considerable light on the question of the manner in 

 which these gases are held to glass. Warburg and Ihmori (36) have 

 maintained that the gases are held by chemical forces (primary valence 

 forces) while other writers have maintained that the gases are held 

 primarily by physical forces (secondary valence forces) . The measure- 

 ments of Warburg and Ihmori were made with water vapor and while 

 no analyses of the glasses were made, it was found that only those 

 glasses that contain alkali were capable of taking up water vapor. 



Glasses Nos. 1, 2, 3, 4, 5 and 6 were experimented with in this con- 

 nection. The glasses were heated to a temperature high enough to 



