Page:Text-book of Electrochemistry.djvu/145

 �I30 CONDUCTIVITY OF ELECTROLYTES. chap.

dip into the cells, A into K and B into Kx, The cells are connected by a narrow tube, My which contains the solution whose resistance, JBi, is to be determined. The ends of this tube are usually closed by a piece of parchment paper or

animal membrane, so that the contents do not mix with the solutions in ^and K\,

There dip also into the ves- sels two Sond electrodes, z and ^1, of amalgamated zinc, which are connected with the quadrant electrometer §. The electrode B is connected with a known resistance (a rheostat), which is joined through G to the pole of a battery, E, the other pole being connected with the electrode A. The points B and G and z and zx can alternately be connected with the electrometer. In the former case the deflection gives the potential difference V between B and (7, and in the second case that Fi between z and z\. If I is the current strength, then we have the following connections : —

and therefore —

i2i : i2 = Fi : r,

from which B\ can be calculated.

In order to determine the specific resistance, the tube is first filled with a liquid of known specific resistance, and fix>m the result obtained the constant for the tube is ascertained \ this method is better than calculating from iZ and the dimen- sions of the tube. It is evident that the resistances of different liquids in the same tube bear the same ratio to each other as the specific resistances.

In place of the quadrant electrometer any other form of electrometer may, of course, be used, e,g. a capillary electro- meter, provided that the conditions of the experiment are suitable.

�� �