Galvanic cell

“ Nothing else, indeed, happens when we make the process continuous by using a galvanic source of electricity. All that distinguishes a galvanic cell from the sources of electricity used before the time of Volta is its faculty of immediately re-establishing the field which prevails between its poles, whenever this field becomes extinguished by the presence of a conductor. ”

“ But his chief interest at the Royal Institution was with electro-chemistry. Galvanic phenomena had already engaged his attention before he left Bristol, but in London he had at his disposal a large battery which gave him much greater opportunities. His first communication to the Royal Society, read in June 1801, related to galvanic combinations formed with single metallic plates and fluids, and showed that an electric cell might be constructed with a single metal and two fluids, provided one of the fluids was capable of oxidizing one surface of the metal ”

“ Hydrogen has a stronger attraction for SO4 than Cu has, so it unites with the SO4, forming H2SO4 (sulphuric acid) , and this at the same time throws out the Cu bodily. This Cu is then free, instead of hydrogen, to be deposited upon the copper plate. The current is constant, as there is no polarization.
286. Various Galvanic Cells; Open and Closed Circuit Cells. There is no one form of cell that is best for all kinds of work. If momentary currents only are wanted, such as for bells, telephones, etc., in which the cell has plenty of time to rest, open circuit cells are used. ”

“ This same year he communicated to the French Academy his invention of the galvanic battery, now bearing his name, in which platinum is substituted for copper, and nitric acid for sulphuric. He also published in this connection a paper on the "Inaction of Amalgamated Zinc in Acidulated Water," in which this phenomenon was first satisfactorily explained. About the same time he discovered that if two pieces of gold are placed one in a cell of nitric and the other in one of hydrochloric acid, separated by an earthen-ware partition, no chemical action takes place ”

“ Richard Owen, Lorenz Oken contends that organism is galvanism residing in a thoroughly homogeneous mass. A galvanic pile, pounded into atoms, must become alive. In this manner, nature brings forth organic bodies. The basis of electricity is the air; of magnetism, metal; of chemism (the name he gives to the influence that produces chemical combination) , salts. The basis of galvanism, in like manner, is the organic mass. Accordingly, whatever is organic is galvanic; whatever is alive is galvanic. Life, organism, galvanism, are one. Life is the vital process ”

“ Galvanism was so called precisely as the Roentgen ray was christened at a later day—as a safe means of begging the question as to the nature of the phenomena involved. The initial fact in galvanism was the discovery of Luigi Galvani (1737-1798) , a physician of Bologna, in 1791, that by bringing metals in contact with the nerves of a frog's leg violent muscular contractions are produced. As this simple little experiment led eventually to the discovery of galvanic electricity and the invention of the galvanic battery, it may be regarded as the beginning of modern electricity. ”

“ It is a powerful agent in nature, and calculated for important ends, of which we are ignorant. It is unnecessary to notice opinions concerning it. All electrics will yield it, such as glass, rosin, &c. and it may be collected in the usual manner by the prime conductor and Leyden jar. Galvanism, called also Galvanic electricity, produced by an arrangement of zinc, and copper plates in a pile, or trough, and placed in contact with some oxygenizing fluid, has the same effect of causing quiescent heat to become distributable, and is undoubtedly the result of chemical action. ”

“ A thin magnetic needle is held in a light, paper sling at F, suspended by a fine, vertical fiber. (From Annales de Chimie et de Physique.)
Cumming considers his straight-wire calibrated “galvanometer” to be a device for “measuring” galvanic electricity; on the other hand, his multiple-loop “galvanoscopes” are for “discovering” galvanic electricity. With the multiplier instrument, he found galvanic effects (i.e., needle deflections) using copper and zinc electrodes with several acids not previously known to create galvanic action. ”

“ If electricity be administered to a patient directly Pg 100 from the conductor, he receives very little of its action; if a shock be given with the Leyden flask, the action is exceedingly strong, but not permanent. On the other hand, the pile has a strong and continued action, and occasions a powerful circulation of the Galvanic matter, which after some time produces very striking effects on the animal fluids. I might here refer, by way of example, to the experiments made with Galvanism on the blood, the bile, and the urine, which gave results I was never able to obtain by common electricity. ”

“ That “galvanism” is something quite different from static electricity was the opinion of many investigators; Hare considered the heat developed to be the distinguishing mark of the electric current. He says: “It is admitted that the action of the galvanic fluid is upon or between atoms; while mechanical electricity when uncoerced, acts only upon masses. This difference has not been explained unless by my hypothesis, in which caloric, of which the influence is only exerted between atoms, is supposed to be a principal agent in galvanism.” ”

“ When the doors are closed, A and B are in darkness; they are practically iso-electric, there being no current in the galvanometer. But exposure of A to light gives rise to a, difference of potential between A and B, A becoming galvanometrically negative, the resulting deflection being in one direction. Exposure of B gives rise to a responsive deflection in the opposite direction. The two leaves serve as the two plates in a voltaic cell; but unlike ordinary voltaic cell with elements of different metals ”

“ This shows that such a long series of experiments could not have been performed by the simple application of metallic coatings. I am of opinion that, in general, these coatings, invented in the first instance by Galvani, are passive. They serve merely to conduct the fluid pre-existent in the animal system; whereas, with the Galvanic batteries of Volta, the muscles are excited to action by the influence of the apparatus itself. ”

“ It is a comforting theory to electro-therapeutists that a galvanometer will enable them to administer their doses of electricity with as much exactitude as we daily prescribe so many grains, or so many minims of ordinary medicines; but, like some other theories which save us much trouble, when adopted as theories only, it fails us in practice (at least according to my experience) , and chiefly so, because a galvanometer can be usefully employed only when it is included in the circuit of a continuous current, as, e.g., in aneurismal electro-puncture ”

“ Fourcroy attributes this phenomenon to the decomposition of water by the galvanic fluid, which abandons the oxygen to the iron that touches the positive extremity of the pile; then conducts the other gas invisibly to the end of the other wire, there to be disengaged.
From the numerous experiments of Mr. Davy, many new and important facts have been established, and Galvanism has been found to be one of the most powerful agents in chemistry. By its influence, platina wire has been melted; gold, silver, copper, and most of the metals, have easily been burnt! ”

“ Wherever matter is found definitely arranged, it is also accompanied by effects dependent upon the arrangement; platinum, zinc, and sulphuric acid, when connected in a proper manner, form a galvanic element and give rise to a galvanic current. ”

“ As soon as it was discovered that galvanic power might be excited by the contact of metals, without the interposition of animal organs, it was imagined that the electricity was set in motion by the contact of bodies possessing different conducting powers, without any reference to the chemical action which accompanied the process. ”

“ The ordinary galvanometer is founded on the principle that a magnetic compass needle has a tendency to place itself at right angles to a current of electricity, and the degree to which the needle is deflected is a measure of the quantity of electricity, but the angle of deflection is not proportionate to the current strength, and it differs in different galvanometers ”

“ Acting upon the hint given by Galvani's accident, this pile was made of thin sheets of metal, say of copper and zinc, laid in series one above the other, with a piece of cloth wet with dilute acid interposed between each sheet and the next. The sheets were connected at the edges in pairs, a sheet of zinc to a sheet of copper, and the pile began with a sheet of one metal and ended with one of the other. It is to be noted that a single pair would have produced the same result as a hundred pairs, only more feebly. A single large pair is, indeed, the modern electric battery of one cell. ”

“ Could the functions of the part be protected against the influence of so powerful an agent, it is evident that, by a galvanic battery of sufficient intensity, a calculus composed of alkaline or earthy salts might be transferred from the bladder by the simple introduction of a double sound, communicating on one hand with the calculus, and, on the other, with two vessels filled with water, in which are plunged the opposite poles of a galvanic apparatus. ”

“ This change in the posi­tion of the legs occurs when the animal is not moving at all, thus showing that the galvano­tropic movements take place not because the animal intends to go to the anode, but that the animal goes to the anode because its legs are practically prevented by the galvanic current from working in any other way. ”

“ The galvanic pile only acts for a few minutes, when introduced into hydrogen, nitrogen, or hydro-carbonate; that is, only as long as the water between its plates holds some oxygen in solution: immerse it for a few moments in water containing air, and it acts again.
It acts very vividly in oxygen gas, and less so in the atmosphere. When its plates are moistened by marine acid, its action is very powerful, but infinitely more so when nitrous acid is employed. Five plates with nitrous acid gave sparks equal to those of the common pile. ”

“ The circumstances of Galvani's original discovery had prepared the minds of philosophers for this belief, which was powerfully supported by the similarity of the physiological effects of the pile to those of the Leyden jar, and by the observation that the galvanic influence was conducted only by those bodies—e.g. the metals—which were already known to be good conductors of static electricity. But Volta now supplied a still more convincing proof. Taking a disk of copper and one of zinc, he held each by an insulating handle and applied them to each other for an instant. ”

“ If a galvanic current passes through any conductor, a metallic wire, or an electrolytic fluid, it evolves heat. Mr. Prescott Joule was the first who proved experimentally that, if no other work is done by the current, the total amount of heat evolved in a galvanic circuit during a certain time is exactly equal to that which ought to have been generated by the chemical actions which have been performed during that time. ”

“ At the same time we learn, that by throwing a beam of light upon a plate of copper which forms one of a galvanic pair, whilst it is under the influence of an acidulated solution, an additional excitation takes place, and the galvanometer will indicate the passage of an increased current of electricity. ”

“ But, as I have said, the electrical phenomena which can be produced by the current along a wire connecting the positive and negative poles of a galvanic battery are not striking. They do not afford effective signals when the distance traversed is very great and the battery not exceptionally strong. Thus, at first, galvanic electricity was not more successful in practice than frictional electricity.
It was not until the effect of the galvanic current on the magnetic needle had been discovered that electricity became practically available in telegraphy. ”

“ I observed the return to original resistance in the following manner:—The sensitive substance was placed at K (Fig. 53) , and formed part of a circuit which included a Daniell cell and galvanometer. At first no current passes. Sparks are then caused at S, and the needle of the galvanometer is permanently deflected. On smartly tapping the table supporting the ebonite cap in which the sensitive substance is contained, the original condition is completely restored. When the electric action has been of a powerful character, violent blows are necessary. ”

“ For this purpose I used a galvanometer.
A cell was made, in the way previously described, with two specimens of magnesium powder. Owing to some differences in the two portions there was an initial P. D. of 0.042 V. between the two electrodes. The E. M. F. of the cell was balanced by the potentiometer method, a sensitive galvanometer (with an interposed high resistance) being used as the detector of electromotive variation. Fig. 39 (a) shows the deviation from the balanced position by radiation which nearly reduced the potential difference to half its original value. ”

“ It is not absolutely necessary to use two metals to produce the galvanic phenomena; for if one side of a metal be made to oxidate, while the other is prevented from oxidation, these appearances will still be produced. It is not indeed necessary to use any metal; for a piece of charcoal, oxidated in the same way, produces galvanism; so does fresh muscular fibre, and perhaps any substance capable of oxidation. The most striking circumstance in galvanism, is, that it accompanies oxidation, and is perhaps never produced without it. ”