CHAPTER XVI. Electro-analysis.
Determination of the Quantity of Salt in a Solution by measuring the Conductivity. — If we know the con- ductivity of solutions of a particular salt at various concen- trations, then inversely by determining the conductivity we can find the concentration.
If we have a solution containing two given salts, then by making two determinations we find the quantity of each pi-esent ; one of the determinations may be the conductivity, the second some other property, such as the total weight of dry substance. Erdmann (1) determines in this way the quantity of potassium chloride in presence of potassium iodide or rubidium chloride, etc.
In many cases the proportions of the constituents present are nearly constant; this is the case, for instance, with different samples of sea water containing varying total amounts of dissolved substance. In such cases the determi- nation of the resistance is sufficient to indicate the quantities present, and this method of analysis has actually been employed.
Occasionally non-electrolytes are present in the solution to be analysed (for instance, in the estimation of the ash of cane sugar or molasses), and these diminish the conductivity. When this happens a correction must be introduced, and the magnitude of this can be ascertained either from the data given on p. 150, or it has to be found by a special experiment.
For some salts, e.f/, silver chloride, the conductivity is
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