598 BELL SYSTEM TECHNICAL JOURNAL 



able departure from flatness may occur without serious effect on the 

 intelHgibiUty of the speech transmission. 



Synthetic patterns used in the analysis of the characteristics are 

 explained and illustrated. Types of audio-frequency distortion result- 

 ing from selective fading are discussed. The effect of frequency or 

 phase modulation in producing distortion on such a circuit is con- 

 sidered. 



Records are shown of the effect of an automatic gain control, follow- 

 ing carrier amplitude variations, upon the audio-frequency transmis- 

 sion characteristic. "Rapid" fading records revealing unlike fading 

 on radio frequencies separated by 170 cycles are included. The sea- 

 sonal variation in susceptibility of the circuit to this "rapid" fading is 

 illustrated. 



The records mentioned above are for ordinary modulated carrier 

 transmission and involve the results of interaction between the two 

 side bands in the detection process. There are also shown records 

 made on single side-band carrier-suppressed transmission. In this 

 case detection does not modify the frequency amplitude relations and 

 the record delineates directly the frequency-amplitude characteristics 

 of the received radio-frequency band. 



Age Hardening Lead-Calcium Alloys.^ Earle E. Schumacher 

 and George M. Bouton. The lead end of the system lead-cal- 

 cium has been investigated and a constitutional diagram given. A 

 peritectic reaction has been discovered and the solid solubility of cal- 

 cium in lead has been determined for five temperatures. The solubility 

 changes from 0.1 per cent calcium at 328.3° C. to approximately 0.01 

 per cent calcium at 25° C. Data for locating the solid solubility curve 

 were obtained from thermal analysis, electrical conductivity measure- 

 ments, microscopic examinations and age hardening studies. 



It has been shown on the basis of laboratory tests that greater tensile 

 strengths and resistances to fatigue failure can be developed in some 

 of the lead-calcium alloys than in the lead — 1 per cent antimony alloy. 

 Certain lead-calcium alloys have been suggested as sheathing materials 

 for electrical cables. 



Preparation of Air of Knoum Humidity and Its Application to the 

 Calibration of an Absolute-Humidity Recorder J A. C. Walker 

 and E. J. Ernest, Jr. An apparatus is described whereby constant 

 flowing mixtures of air and water vapor may be prepared, in which the 

 moisture content varies not more than 0.001 per cent by volume, over 



6 Metals & Alloys, Mar., 1930. 



' hid. and Engg. Chem., Api, 15, 1930. 



