From an analytical point of view, little can be done with a conductance reading, however accurate it may be, unless it can be related to chemical concentration via a table or graph. Much data has been generated in the past 100 years in this area, but a comprehensive gath- ering of the information in a form useful to industry has been lacking1. It is hoped that the following will provide a ready and reasonably accurate reference of conduc- tance values for the majority of electrolytes encoun- tered in industrial situations.
The information is presented in graphical form to per- mit rapid evaluation of response patterns and to elimi- nate the time consuming and often impractical (because of non-linearity) extrapolation required in tables with widely separated concentrations. This method of presentation sacrifices the precision gained by listing actual values, but the accuracy retained is more than sufficient for the great majority of industrial uses. The intent has been to provide a useful working tool more so than a scientific reference.
Most of the data presented is the result of extremely careful and accurate laboratory work conducted by various researchers over the years. It is recognized that older sources of information, notably the extensive International Critical Tables, have been found to be slightly inaccurate due to changes in the definition of basic units in recent times as well as to erroneous alignment procedures and measurement techniques. However, with the previously stated area of application in mind, these minor errors are of little significance and may safely be ignored.
A few curves are based on more casual “field condi- tion” observations, and others are derived from data with a low degree of resolution in the original refer- ence. Both will be marked with a single asterisk (*) in the index that follows.
All conductance values have been referenced to a sin- gle temperature of 25°C for convenience (isothermal plots are given for selected chemicals of major impor- tance). Much of the original data was presented at this temperature, and all sources fell in the range of 15° to 25°C. Where possible, the temperature correction fac- tor was calculated from isothermal equivalent conduc- tances listed in the International Critical Tables. An average was taken over as wide a range as possible from .5N to 5N and 0-25°C. When such a calculation was not possible, the widely accepted “average” of 2%/°C was used. Temperature factors, of course, will vary in a non-linear manner with respect to both tem- perature and concentration for many chemicals, but the small size of the adjustments render this of little impor- tance. As the majority of corrections involved differen- tials of only 5° or 7°C, errors introduced from this source will be small. With this in mind, the final effect of temperature correction error deserves further com- ment.
The relative conductance values at various concentra- tions would not be noticeably affected. The error could be approximately but correctly described as relating to the reference temperature rather than conductance. Too much or too little correction simply means that the curve shown is really that seen at 24° or 26° rather than the indicated 25°. It is not anticipated that errors will exceed the +1° examples given in any except the most unusual cases.
No guarantees of accuracy can be given, but most of the data should easily fall within 5% of the correct absolute value. The choice of curve shape through data points will be a factor in some cases, and it is for this reason that the points were clearly indicated. (Some were omitted in the lower portions of the scale for the sake of clarity.)