MAXIMUM SPECIFIC ELECTRICAL CONDUCTIVITY IN CHEMISTRY. 125 
submaximal solution, but it cannot be converted into a maximal solution by merely 
adding water. It is thus sub-ultramaximal. 
Similarly, a solution may be sub-premaximal, in which case it will gain in con- 
ductivity on becoming more concentrated by loss of water, but cannot become a 
maximal solution by mere increase of concentration. 
All such solutions may be expected to gain in conductivity as a result of the 
polymerisation * of the molecules of non-electrolytes or weak electrolytes which they 
contain. 
The greater the concentration of the non-electrolyte present, the greater is the 
possible gain in conductivity due to its polymerisation, and accordingly the greater is 
the tendency, cxtervs paribus, for such polymerisation to take place. The tendency 
towards polymerisation is not confined to solutions having a concentration of the 
electrolyte on one side only of maximum conductivity, but clearly belongs to sub- 
premaximal solutions as well as to sub-ultramaximal solutions. 
In the synthesis of organic compounds, polymerisation or condensation without 
dehydration is often brought about by means of strong electrolytes. It is probable 
that these reagents will be found, as a rule, most effective for this purpose in the form 
of premaximal solutions. Where condensation or polymerisation accompanied by 
dehydration is desired, ultra-maximal solutions will prove, generally speaking, more 
effective. 
Hypbrocutoric Actp AND CoBALT CHLORIDE. 
Concentrated solutions of hydrogen chloride change the pink colour of hydrated 
cobalt chloride to a blue-green. A similar colour change is produced if the crystallised 
salt be heated so as to drive off water of crystallisation. Granting that the change of 
colour in the first case is also accompanied by dehydration, the assumption of a tendency 
towards increased specific conductivity suggests that premaximal solutions of hydro- 
-ehlorie acid should not cause the change of colour, because such solutions lose in 
conductivity by dilution. To test this, 50 c.c. each of a series of solutions of HCl of 
known concentration were severally mixed with two drops of a concentrated aqueous 
solution of cobalt chloride, and then arranged side by side, in order of concentration of 
HCl. It was then seen that in the weaker solutions up to 16 per cent. HCl, the pink 
colour was not altered. A solution of 18°2 per cent. HCl showed only a faint tinge of 
purple, but once past this latter concentration the change in colour was more and more 
marked. Using cobalt chloride as an indicator, it is quite easy in this way to make up 
a solution containing very nearly 19 per cent. HCl without any measurement or 
weighing. 
Solutions of hydrobromic acid showed a similar behaviour with cobalt chloride. 
* The term “polymerisation” is here intended to include cases of condensation of the aldol type which are not 
accompanied by a permanent hydrolysis or dehydration, 
TRANS. ROY. SOC. EDIN., VOL, XLVIII. PART I. (NO. 6). 20 
