Voltaic. adj.
This adjective is used to qualify a great many things appertaining to or connected with current electricity. It is derived from Volta, the inventor of the voltaic battery, and now tends to displace the term "galvanic," formerly in general use.
Voltaic Alternatives.
A term used in electro-therapeutics or medical electricity to indicate an alternating battery current.
Synonym--Alternative current.
Voltaic Effect.
The potential difference developed by contact of different conductors.
It is the basis of the contact theory, q. v., of electricity, although it may be accepted as the expression for a condition of things by those who reject the above theory. This potential difference is slight when the conductors are separated, but it is calculated that it would be enormous could the metals be so quickly separated as to hold each its own charge.
Thus if a copper and a zinc plate are a.s.sumed to be in contact, really 1/20000000 centimeter or 1/50000000 inch apart, they may be treated as a pair of condenser plates. Being so near, their density of charge, which is a strongly bound charge, is enormous. If it were possible to separate them without permitting any discharge, their potential would rise by the separation, on the principle of Epinus" condenser, q. v., to such an extent that they would spark through twenty feet of air. (See Volta"s Fundamental Experiment.)
Voltaic Electricity.
Electricity of low potential difference and large current intensity; electricity such as produced by a voltaic battery; current or dynamic electricity as opposed to static electricity.
Voltameter.
In general an apparatus for determining the quant.i.ty of electricity pa.s.sing through a conductor by measuring the electrolytic action it can perform.
Voltameter, Copper.
An apparatus which may be of similar construction with the silver voltameter (see Voltameter, Silver), but in which a copper anode and a solution of copper sulphate are subst.i.tuted for the silver anode and silver nitrate solution. One coulomb corresponds to .329 milligram or .005084 grain of copper deposited. It is not accepted as of as high a standard as the silver voltameter.
The electrodes should be placed half an inch from each other. Two square plate electrodes may conveniently be used, and not less than two square inches on each plate should be the area per ampere of current.
564 STANDARD ELECTRICAL DICTIONARY.
Voltameter, Differential, Siemens".
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.
Voltameter, Gas.
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 gla.s.s 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 c.o.c.ks 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 0? (32? F.) and 76 centimeters, or 30 inches barometer.
Fig. 341. GAS VOLTAMETER.
565 STANDARD ELECTRICAL DICTIONARY.
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 + F? - 32) ) / (h* 491)
For the metric measurements and degrees C.
(.1738 * 76 * (273 + C?)) / (h X 273)
Voltameter, Silver.
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 pa.s.sed 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.
FIG. 342. SILVER VOLTAMETER.
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.
566 STANDARD ELECTRICAL DICTIONARY.
Voltameter, Weight.
A voltameter in which the amount of decomposition is determined by weighing the products, or one of the products of the electrolysis. The t.i.tles Voltameter, Copper, and Voltameter, Silver, may be cited.
Fig. 343. WEIGHT VOLTAMETERS.
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.