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 James Clerk Maxwell
   
 
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Lettera a  W. GARNETT, 25 agosto  1877
 
TO THE SAME.

                                                                    Glenlair, 25d August 1877.

     I have been copying Cavendish on the resistance of electrolytes. If there is any one who would try a few of them   roughly in the U tube, it might be interesting to compare with Cavendish's results. For weak solutions Kohlrausch  may be referred to.

                                     Sea Salt (Chloride of Sodium.)
                                     Experiments in January 1781.
 
 
Watered to
1 of Salt.
Resistance Resistance
x quantity of Salt
Saturated sol. 3·78      1 ·602
12 1·91 ·500
30 3·97 ·475
70 8·8 ·475
143 15·75 ·416
1000 93·02  ·352
20,000 18·23 ·345

     Salt in 20,000 conducts about 7 times better than distilled water.

     Salt in 69 of water conducts 1.97 times better at 105° F. than at 58 1/2°.

     If Professor Liveing is in Cambridge, could you ask him to put me in the way of finding the best book on chemistry  for the year 1777, so as to obtain the equivalents and the names of salts used by Cavendish?

     The numbers in the first columns are the quantities which were equivalent to the "acid " in solution of 1 of salt 29 of   water.

     3·2 Sal Sylvii (potassium chloride).

     2·3 Sal Amm. (ammonium chIoride).

     14·10 Calc. S.S.A. (?)

     2·21 Calcined Glauber's Salt (sodium sulphate).

     3·17 Quadrangular Nitre (sodium nitrate).

     5·19 Salt D. (?)

     The solutions were 3, 10, 12.

     I am going to try if this is Troy or Apothecaries' weight.

     Saturated solution (1 in 3·78) of common salt has 437,000 the resistance of iron wire. New distilled water has    more resistance than distilled water kept a year.

     All these results and many more were got by comparison of the strength of shocks taken through Cavendish's   body. I think this series of experiments is the most wonderful of them all, and well worth verification.

                                             · · · · · ·

     Cavendish is the first verifier of Ohm's Law, for he finds by successive series of experiments that the resistance is    as the following power of the velocity, 1·08, 1·03, ·980, and concludes that it is as the first power. All this by the   physiological galvanometer.

     . . . Can you solve the equation

     z = A/xy is a solution. Find the general ditto.