1914-15.] Conductivity of Salt-saturated Hydrochloric Acid. 143 
In other words, at a certain concentration not far from 5 per cent., a solution 
of hydrogen chloride may be saturated with salt without the conductivity 
of the solution being affected. 
The maximum of conductivity is stated by Kohlrausch to occur in 
aqueous hydrochloric acid at about 18 per cent., but full and accurate 
determinations of the conductivities of this acid communicated to this 
Society by Professor J. Gibson, but as yet unpublished, show the maximum 
to occur very close to 19T per cent. In a salt-saturated solution the 
maximum occurs at a higher concentration, very nearly 21 ’9 per cent. 
16 18 20 22 24 26 28 30 
Fig. 2. 
according to fig. 2, or 21 ’5 per cent, if the concentration of hydrogen 
chloride be considered in relation to the total weight of solution. 
It has been seen that, under certain conditions, the initiation of a 
chemical change by a mineral acid may be determined by the concentration 
of the acid being greater or less than the concentration of the acid which 
has maximum conductivity. As regards the occurrence of certain chemical 
changes in which hydrochloric acid may play a part, the acid containing 
19T per cent, of hydrogen chloride is of critical concentration. It is 
interesting to find out, if possible, whether the critical concentration in the 
case of the salt-saturated hydrochloric acid is also the same as that of the 
solution having maximum conductivity. 
