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.
