[ 03 ] 
IL The Electrical Conductivity and Luminosity of Flames containing 
Salt Vapours. 
By H. A. Wilson, F.R.S., Professor of Physics, Rice Institute, Houston, 
Texas, U.S.A. 
Received 31 May,—Read June 17, 1915. 
When the vapour of an alkali salt is present in a Bunsen flame the vapour becomes 
luminous and also increases the electrical conductivity of the flame. The fraction of 
the salt molecules which are luminous is probably very small, and unless the concen¬ 
tration of the salt vapour is very small the fraction of the salt molecules which are 
charged electrically, or are ionised, is also very small. 
Any particular salt molecule enters the flame at the bottom and moves up the 
flame with the velocity of the flame gases which is of the order of 200 cm. per second. 
The molecule is therefore in the flame for only a small fraction of a second, but this 
time interval is probably long enough for a state of equilibrium to be established 
between the several states in which the molecules can exist. For example, in the 
case of sodium chloride there is probably an equilibrium between NaCl, NaOH, 
Na 2 0, Na, H 2 0, HCL, and possibly other bodies such as CO, C0 2 , and Na 2 C0 3 . 
Each sodium atom must exist in the flame successively in different states and will, 
on the average, exist in each state a definite fraction of the time it is in the flame. 
Of course the time interval may not be long enough for every atom to pass through 
all the possible states, but on the average there will be a definite fraction of all the 
sodium at.oms in each possible state. In some of the possible states the atoms may 
be luminous during the whole or during only a fraction of the time the atoms are in 
those states, and during the whole or a part of the time the atoms are in any state 
they may be positively charged and so form ions. The object of the experiments 
described in this paper was to obtain information about the relative numbers of the 
atoms in the different possible states, especially the luminous state and the positively- 
charged state, and about the nature of the luminous state and the charged state. 
In an electric field the charged molecules or ions tend to move with a definite 
velocity proportional to the electric intensity. This velocity will be denoted by 
AX, where Jc is the velocity due to unit held and X the field strength. The average 
velocity, over a long time, of any particular metal atom due to the field will be fkH, 
where f denotes the fraction of the time during which the atom is in the positively- 
charged state. The time during which the atoms are in the flame may not be long 
enough for each atom to pass through all the possible states, so that actually only 
VOL. CCXVI.-A 539. K [Published November 29. 1915. 
