The volt based upon the congress or legal ohm; the legal volt.

The volt based on the B. A. ohm. It is equal to .9889 legal volt.

In a compound circuit, consisting of a number of different metals, all
points of which are at the same temperature, there is no current.

The electro-motive force between any two metals in an electro-chemical
series (see Electro-Chemical Series) is equal to the sum of the
electro-motive forces between all the intervening metals.

The moistened finger is placed on the upper plate of a condensing or
electrophorous electroscope. The other hand holds a plate of zinc z,
soldered to a plate of copper c. The lower plate is touched with the
copper. On removing the cover the gold leaves l diverge and with
negative electricity. Hence zinc is supposed to be positively
electrified when in contact with copper. The experiment is used to
demonstrate the contact theory of electricity.

The law on which voltameters are based. The amount of chemical
decomposition produced by an electric current in a given electrolyte is
proportional to the quantity of electricity passed through the solution.

A voltameter in which the amount of decomposition is determined by
weighing the products, or one of the products of the electrolysis. The
titles Voltameter, Copper, and Voltameter, Silver, may be cited.

In the cuts are shown examples of weight gas voltameters. These are
tubes light enough to be weighed when charged. Each contains a
decomposition cell T, with its platinum electrodes, and charged with
dilute sulphuric acid, while t is calcium chloride or other drying agent
to collect any water carried off as vapor or as spray by the escaping
gases; c are corks placed in position when the weighing is being
executed, so as to prevent the calcium chloride from absorbing moisture
from the air.

In use the tubes are weighed. They are then connected to the circuit,
after removal of the corks, and the decomposition proceeds. After a
sufficient time they are removed, the corks put in place, and they are
weighed again. The loss gives the water decomposed.

The water corresponding to one coulomb is

.09326 milligram   .001430 grain,   Ayrton,
.092      “                         Hospitalier,
.0935     “                         Daniell.

An apparatus consisting of a platinum vessel containing a solution of
silver nitrate into which solution a silver anode dips, whose end is
wrapped in muslin to prevent the detachment of any particles. When a
current is passed by connecting one terminal to the dish and the other
to the rod, securing a proper direction of current, silver will be
deposited on the dish and the same amount will be dissolved from the
rod. The dish is weighed before and after the test. Its increase in
weight gives the silver deposited.

In the cut Ag is the silver anode, Pt is the platinum dish, r is the
conducting rod, p is a wooden standard, Cu is a copper plate on which
the dish rests and which also serves as a conductor and contact surface,
b is a muslin cloth to place over the silver plate to prevent detached
particles falling in the dish; s s’ are the binding screws.

The weight of silver corresponding to a coulomb is given variously by
different authorities. Ayrton and Daniell take 1.11815 milligrams or
.017253 grain of metallic silver. Other determinations are as follows:
1.1183 milligrams   (Kohlrausch).
1.124   “           (Merscart).

The solution of silver nitrate should be from 15 to 30 per cent. of
strength. The current should not exceed one ampere per six square
inches; or in other words not more than about 3/1000 grain of silver
should be deposited per second on a square inch area of the dish. The
edge of the silver disc or anode should be about equidistant from the
side and bottom of the dish. The latter notes are due to Lord Rayleigh.

A voltameter whose indications are based on the electrolysis of water,
made an electrolyte by the addition of sulphuric acid. The gases evolved
are measured. It may take several forms.

In one form it is an apparatus consisting of a single eudiometer or
graduated glass tube with upper end closed and its lower end or mouth
open, collecting the mixture of hydrogen and oxygen.

In the form shown in the cut three tubes are connected, the side tubes
representing eudiometers. For each side tube there is a platinum
electrode. In this apparatus the oxygen and hydrogen are connected in
opposite tubes. A is an open tube filled with dilute sulphuric acid. By
opening the cocks on B and C they can both be completely filled with
acid. As shown in the cut, this operation is not yet completed. The
hydrogen alone may in this case be measured.

The mixed gas voltameter has only one eudiometer.

The exact equivalents are only approximately known. The volume of mixed
gases per coulomb is given as .1738 cubic centimeters (Ayrton); .172
cubic centimeters (Hospitalier); and other values by other authorities.
The hydrogen is equal to 1/3 of the mixed gases almost exactly.

Synonyms–Volume Voltameter–Sulphuric Acid Voltameter.

The gas is measured at 0º (32º F.) and 76 centimeters, or 30 inches
barometer.

If the gas is measured in cubic inches, the temperature in degrees F.,
and the barometric height in inches, the following formula may be used
for reduction to standard pressure and temperature. It is the volume
corresponding to one coulomb.
( .01058 * 30 * (491 + Fº – 32) ) / (h* 491)

For the metric measurements and degrees C.
(.1738 * 76 * (273 + Cº)) / (h X 273)

A volume or gas voltameter with duplicate eudiometers and pairs of
electrodes. It is used for determining the resistance of the platinum
conductor used in his pyrometer. A current divides between the two
voltameters; in one branch of the circuit the platinum conductor is
placed, in the other a known resistance. The current strength varying
inversely with the resistance, the resistances of the two conductors are
inversely proportional to the gas evolved.