ABSTRACTS OF TECHNICAL ARTICLES 401 



atoms, the ratio of the adsorptive capacity to the total adsorbing sur- 

 face would appear to be much more satisfactory for a measure of the 

 activity. 



The data shown graphically in this paper show that starting with a 

 given raw material, i.e., an anthracite coal, an increase in the tempera- 

 ture to which the material is heated above 1000° decreases the adsorp- 

 tive capacity per unit pore volume. It is pointed out that the pore 

 volume may be considered a measure of the extent of adsorbing sur- 

 face and that the activity of an adsorbent carbon (charcoal) should be 

 measured by the amount of gas adsorbed per unit area of its surface. 

 The data, therefore, indicate that the activity of a charcoal is indepen- 

 dent of the atmosphere in which it is prepared and dependent only on 

 the maximum temperature to which it is heated. At any temperature 

 between 900 and 1300° an increase in the adsorptive capacity is most 

 probably accompanied by a proportional increase in the extent of the 

 adsorbing surface. For example, although the adsorptive capacity 

 of the samples prepared at 1100° ranged from 1.8 to 23.1 c.c. carbon 

 dioxide per gram at 0° and atmospheric pressure, the actually meas- 

 ured values of activity ranged from 0.201 to 0.295, while the weighted 

 average for all the samples prepared at the same temperature was 0.27 : 

 the variations observed are believed to be due to the limitations, which 

 have been discussed, of the measure of the surface area rather than to 

 a real difference in the activity. 



The Operation of Modulators from a Physical Viewpoint.^ E. 

 Peterson and F. B. Llewellyn. The mathematical expressions 

 which occur in the treatment of non-linear devices as circuit elements 

 are interpreted in terms of a graphical physical picture of the processes 

 involved. This picture suggests, in turn, several useful ways of apply- 

 ing the equations in cases where the driving forces are so large that the 

 ordinary power series treatment becomes prohibitively cumbersome. 

 In particular, the application has been made in detail to the calculation 

 of the intermediate-frequency output to be expected from a heterodyne 

 detector having an incoming radio signal and locally generated beating 

 oscillator voltage applied on its grid and a circuit of finite impedance 

 to the intermediate frequency attached to its plate. 



A Study of the Output Power Obtained from Vacuum Tubes of Different 

 Types} H. A. Pidgeon and J. O. McNally. Economical operation 

 of the large number of tubes involved in the Bell System makes nec- 

 essary the adoption of common supply voltages. This requires that 



* Proc. The Inst. Radio Engineers, Jan. 1930. 

 ^ Proc. The Inst. Radio Engineers, Feb. 1930. 



