y 
1914-15.] Conductivity of Salt-saturated Hydrochloric Acid. 145 
mixtures, that one has maximum conductivity which could be prepared 
by adding salt to hydrochloric acid containing 21 '9 per cent, of hydrogen 
chloride. Of solutions of hydrogen chloride alone, in water, that containing 
19’1 per cent, hydrogen chloride has maximum conductivity. 
(3) The critical concentration of hydrogen chloride at which hydro- 
chloric acid is able to afiect the colour of cobalt chloride is changed, in 
the same sense as the concentration of hydrogen chloride corresponding 
to maximum conductivity is changed, by saturating the solution with salt. 
(4) A new form of conductivity cell is described. It is specially 
suitable for solutions which are saturated with dissolved solid, or contain 
a volatile solvent. 
Heriot-Watt College, 
Edinburgh. 
(Issued separately April 27 , 1915 .) 
VOL. XXXV. 
10 
