Fog Formation 



177 



scopic substance. Its ability to condense moisture is indicated by the 

 titration of the fog' collected from a small Cottrell precipitatoi'. The 

 acid so obtained had a concentration approximately normal. 



Nitric oxide (NO) is first formed in the discharge. This combines 

 quantitatively with the ozone which is also present" unless the tem- 

 perature is too high, to give the nitrogen pentoxide. According to this 

 reasoning those conditions which give the maximum product of the con- 

 centrations of ozone and of nitrogen pentoxide should produce the most 

 fog. The curves given, figures 1, 2 and 3, which are typical of a very 



x^w 



Pn)narj Uafts 



Fig. 3. The foimation of ozone, nitric acid and fog in air which was undergone 

 discharge in contact with fragments of quartz glass : cf. Anderegg and Bowers, A 

 Type of Silent Dischai-ge Involving Catalysis, page 177. 



large number of similar curves, indicate the validity of this reasoning. 



It was observed that the fog developed to a maximum during the 

 course of a run and then gradually diminished in strength at a rate 

 which depended upon the flow rate of the air. The cause for this was 

 the cooling effect of the evaporation of moisture into the air reduced 

 the temperature sufficiently to lower the amount of moisture evaporated 

 below the condensation point. 



The reason for the passage of these fume particles has been ex- 

 plained by Bancroft" as due to the adsorption of a layer of air on the 

 surface which acts like a cushion to prevent the droplet of nitric acid 

 solution from coming in contact with the alkaline absorbing liquid. 



sWulf, Daniels and Karrer. J. Am. Chem. Soc. 44, 2402 (1922). 

 ° Bancroft. Applied Colloid Chemistry, pp. 65-78 (1921). 



