July 7, 1905.] 



SCIENCE. 



17 



Relation between Ionization and Combustion 



in Flames: F. L. Tufts. 



This paper was a preliminary communica- 

 tion concerning work that is still in progress. 

 The method employed in determining the elec- 

 trical conductivity of a flame has been de- 

 scribed in a previous paper (Pliysihalisclie 

 Zeitsclirift, 5 Jahrgang, No. 3, pp. 76-80), 

 and some results of applying it to a study of 

 combustion have been given in an extract 

 published in the Physical Review (Vol. XX., 

 No. 3, p. 186). The present paper gave the 

 results of investigations carried on for the 

 purpose of determining the influence, on the 

 electrical conductivity of a gas flame, of mix- 

 ing C0„ or air with the illuminating gas be- 

 fore supplying it to the burner. 



The results showed that for small flames, 

 showing little carbon luminosity, the admix- 

 ture of either COo or air caused no marked 

 increase in the electrical conductivity, the 

 araount of gas consumed per second being 

 kept constant. For very small flames the 

 admixture of either caused a decrease in the 

 conductivity. For large flames, however, the 

 admixture of either CO, or air caused an in- 

 crease in the conductivity, which continued 

 until enough CO, or air had been added to 

 destroy the carbon luminosity, when the con- 

 ductivity was as much as twenty-flve per cent, 

 larger than for a flame consuming the same 

 quantity of undiluted gas. Continuing the 

 addition of CO, beyond this point caused a 

 decrease in the conductivity until the flame 

 was extinguished. Continuing the addition 

 of air caused at first a slight decrease, until 

 the inner blue cone became well developed, 

 when the further addition of air caused an 

 increase in the conductivity, the conductivity 

 reaching a larger value than it had on the 

 disappearance of the carbon luminosity. 



The Rate of Recomhination of the lo-ns in 



Air: L. L. Hendren. 



The experiments described were undertaken 

 to determine by a somewhat new method the 

 absolute value of the coefiicient of recombina:- 

 tion of ions in air and more especially its 

 variation with the pressure. The ionizing 

 agent was a very active solution of radium 



chloride spread over the surfaces of two large 

 parallel metal plates. By this means a very 

 large ionization was obtained compared with 

 that obtained by previous observers using the 

 Eontgen rays. The results showed that as the 

 pressure decreases the coefficient of recombina- 

 tion decreases with an increasing rate from a 

 value of 5,500 at atmospheric pressure to 1,000 

 at 10 mm. pressure. 



Radiation Pressure and Differential Tones: 



G. B. Pegram. 



It was pointed out that the differential 

 tones heard on sounding loudly two tones of 

 different pitch may be considered as arising 

 from the radiation pressure of the sound 

 waves acting on the ear-drum. While the 

 question of radiation pressure, or the pressure 

 'on any surface that is reflecting or absorbing 

 energy coming up to it, has not admitted of a 

 general treatment, such a pressure, propor- 

 tional to the energy per unit volume of the 

 medium transmitting the energy has been 

 shown theoretically to exist in many cases, 

 and proven experimentally in some. In the 

 case of sound waves the theoretical treatment 

 of the pressure on a reflecting surface is not 

 at present satisfactory (see Poynting, Phil. 

 Mag., April, 1905), but experimentally it has 

 been measured by Altberg and shown by Wood 

 in a striking manner by an experiment de- 

 scribed in the Physical Review. 



Now if two tones of different pitch are 

 sounded together, beats ensue, so the amount 

 of energy coming up to the ear varies period- 

 ically with the rise and fall in loudness of the 

 resultant sound. But when the most energy 

 is coming up to the ear, or when the sound is 

 loudest, the radiation pressure on the ear- 

 drum is greatest; when the energy coming up 

 to the ear is least, or when the sound is faint- 

 est, the radiation pressure is least. The effect 

 of this variation of pressure on the ear-drum 

 will be to set it into vibration with a period 

 equal to that of the beats, and so, if the beats 

 are of proper frequency, cause the sensation 

 of a tone of that frequency, that is, the differ- 

 ential tone of Helmholtz. 



While this explanation of differential tones 

 from the standpoint of radiation pressure has. 



