144 Messrs. A. Smithells, H. M. Dawson, and H. A. Wilson. 



2. Apparatus. 



The apparatus employed consisted essentially of the arrangement 

 used in other investigations of flame,* whereby the two cones that 

 constitute the flame of a Bunsen burner, can be separated widely and 

 maintained apart for any length of time. The gas and air supplies 

 were regulated with great care, and the air supply was made to actuate 

 a sprayer, whereby an extremely fine spray of any salt solution could 

 be led into the flame. The devices used in regulating the gas and air 

 supplies, and the precautions necessary in the construction and use of 

 the sprayer, are described in the paper. 



The electrode system which usually consisted of two coaxial cylinders 

 of platinum-iridium alloy, was fixed symmetrically in the space between 

 the two cones of the flame. 



The source of electricity consisted of three accumulators, from which 

 by means of a German-silver wire, 20 metres long, and two contact 

 pieces, any E.M.F. up to 5*7 volts could be used. For higher E.M.F.'s 

 Leclanche cells were used. 



3. Method of Working. 



After the apparatus had been adjusted, the current in either direction 

 between the electrodes was measured by a Kelvin high resistance 

 galvanometer for a series of E.M.F.'s. The constancy of the apparatus 

 was tested at intervals during the progress of the experiments by 

 measuring the conductivity due to a y^th normal solution of potassium 

 bromide, and the results were satisfactory. 



4. Conductivity of the Free Flame. 



From the observed conductivity due to a salt, it was necessary to 

 deduct the conductivity of the flame gases alone, and that of the water 

 in the spray. This value, which is very small, was determined by 

 measurements made when distilled water only was sprayed. 



5. Unipolar Conduction. 



Considerable unipolar effects were noticeable in the experiments, 

 and measurements of these are given in the paper. 



6. Measurement of the Concentration of Salt-vapour in the Flame. 



It was not necessary for the purpose of the enquiry to determine the 

 absolute amount of salt between the electrodes ; but for the purpose of 

 instituting some comparison with the results of Arrhenius, a rough 



* Smithells, ' Phil. Mag.,' vol. 39, p. 122, 1895. 



