1. As to the additional reference letters, I is a condenser J the source

of light, and K a reflector. The positive film is moved intermittently but swiftly throughout its length between the objective lens and a beam of light coming through the condenser, being exposed by the shutter during the periods of rest. This results in a projection of the photographs upon a screen in such rapid succession as to present an apparently continuous photograph of the successive positions of the moving objects, which, therefore, appear to the human eye to be in motion. The first claim of Reissue Patent No. 12,192 describes the film. It reads as follows: "An unbroken transparent or translucent tape-like photographic film having thereon uniform, sharply defined, equidistant photographs of successive positions of an object in motion as observed from a single point of view at rapidly recurring intervals of time, such photographs being arranged in a continuous straight-line sequence, unlimited in number save by the length of the film, and sufficient in number to represent the movements of the object throughout an extended period of time." XVI. EDISON'S ORE-MILLING INVENTIONS THE wide range of Edison's activities in this department of the arts is well represented in the diversity of the numerous patents that have been issued to him from time to time. These patents are between fifty and sixty in number, and include magnetic ore separators of ten distinct types; also breaking, crushing, and grinding rolls, conveyors, dust-proof bearings, screens, driers, mixers, bricking apparatus and machines, ovens, and processes of various kinds. A description of the many devices in each of these divisions would require more space than is available; hence, we shall confine ourselves to a few items of predominating importance, already referred to in the narrative, commencing with the fundamental magnetic ore separator, which was covered by United States Patent No. 228,329, issued June 1, 1880. The illustration here presented is copied from the drawing forming part of this patent. A hopper with adjustable feed is supported several feet above a bin having a central partition. Almost midway between the hopper and the bin is placed an electromagnet whose polar extension is so arranged as to be a little to one side of a stream of material falling from the hopper. Normally, a stream of finely divided ore falling from the hopper would fall into that portion of the bin lying to the left of the partition. If, however, the magnet is energized from a source of current, the magnetic particles in the falling stream are attracted by and move toward the magnet, which is so placed with relation to the falling material that the magnetic particles cannot be attracted entirely to the magnet before gravity has carried them past. Hence, their trajectory is altered, and they fall on the right-hand side of the partition in the bin, while the non-magnetic portion of the stream continues in a straight line and falls on the other side, thus effecting a complete separation. This simple but effective principle was the one employed by Edison in his great concentrating plant already described. In practice, the numerous hoppers, magnets, and bins were many feet in length; and they were arranged in batteries of varied magnetic strength, in order that the intermingled mass of crushed rock and iron ore might be more thoroughly separated by being passed through magnetic fields of successively increasing degrees of attracting power. Altogether there were about four hundred and eighty of these immense magnets in the plant, distributed in various buildings in batteries as above mentioned, the crushed rock containing the iron ore being delivered to them by conveyors, and the gangue and ore being taken away after separation by two other conveyors and delivered elsewhere. The magnetic separators at first used by Edison at this plant were of the same generality as the ones employed some years previously in the separation of sea-shore sand, but greatly enlarged and improved. The varied experiences gained in the concentration of vast quantities of ore led naturally to a greater development, and several new types and arrangements of magnetic separators were evolved and elaborated by him from first to last, during the progress of the work at the concentrating plant. The magnetic separation of iron from its ore being the foundation idea of the inventions now under discussion, a consideration of the separator has naturally taken precedence over those of collateral but inseparable interest. The ore-bearing rock, however, must first be ground to powder before it can be separated; hence, we will now begin at the root of this operation and consider the "giant rolls," which Edison devised for breaking huge masses of rock. In his application for United States Patent No. 672,616, issued April 23, 1901, applied for on July 16, 1897, he says: "The object of my invention is to produce a method for the breaking of rock which will be simple and effective, will not require the hand-sledging or blasting of the rock down to pieces of moderate size, and will involve the consumption of a small amount of power." While this quotation refers to the method as "simple," the patent under consideration covers one of the most bold and daring projects that Edison has ever evolved. He proposed to eliminate the slow and expensive method of breaking large boulders manually, and to substitute therefor momentum and kinetic energy applied through the medium of massive machinery, which, in a few seconds, would break into small pieces a rock as big as an ordinary upright cottage piano, and weighing as much as six tons. Engineers to whom Edison communicated his ideas were unanimous in declaring the thing an impossibility; it was like driving two express-trains into each other at full speed to crack a great rock placed between them; that no practical machinery could be built to stand the terrific impact and strains. Edison's convictions were strong, however, and he persisted. The experiments were of heroic size, physically and financially, but after a struggle of several years and an expenditure of about $100,000, he realized the correctness and practicability of his plans in the success of the giant rolls, which were the outcome of his labors. The giant rolls consist of a pair of iron cylinders of massive size and weight, with removable wearing plates having irregular surfaces formed by projecting knobs. These rolls are mounted side by side in a very heavy frame (leaving a gap of about fourteen inches between them), and are so belted up with the source of power that they run in opposite directions. The giant rolls described by Edison in the above-named patent as having been built and operated by him had a combined weight of 167,000 pounds, including all moving parts, which of themselves weighed about seventy tons, each roll being six feet in diameter and five feet long. A top view of the rolls is shown in the sketch, one roll and one of its bearings being shown in section. In Fig. 2 the rolls are illustrated diagrammatically. As a sketch of this nature, even if given with a definite scale, does not always carry an adequate idea of relative dimensions to a non-technical reader, we present in Fig. 3 a perspective illustration of the giant rolls as installed in the concentrating plant. In practice, a small amount of power is applied to run the giant rolls gradually up to a surface speed of several thousand feet a minute. When this high speed is attained, masses of rock weighing several tons in one or more pieces are dumped into a hopper which guides them into the gap between the rapidly revolving rolls. The effect is to partially arrest the swift motion of the rolls instantaneously, and thereby develop and expend an enormous amount of kinetic energy, which with pile-driver effect cracks the rocks and breaks them into pieces small enough to pass through the fourteen-inch gap. As the power is applied to the rolls through slipping friction-clutches, the speed of the driving-pulleys is not materially reduced; hence the rolls may again be quickly speeded up to their highest velocity while another load of rock is being hoisted in position to be dumped into the hopper. It will be obvious from the foregoing that if it were attempted to supply the great energy necessary for this operation by direct application of steam-power, an engine of enormous horse-power would be required, and even then it is doubtful if one could be constructed of sufficient strength to withstand the terrific strains that would ensue. But the work is done by the great momentum and kinetic energy obtained by speeding up these tremendous masses of metal, and then suddenly opposing their progress, the engine being relieved of all strain through the medium of the slipping friction-clutches. Thus, this cyclopean operation may be continuously conducted with an amount of power prodigiously inferior, in proportion, to the results accomplished. The sketch (Fig. 4) showing a large boulder being dumped into the hopper, or roll-pit, will serve to illustrate the method of feeding these great masses of rock to the rolls, and will also enable the reader to form an idea of the rapidity of the breaking operation, when it is stated that a boulder of the size represented would be reduced by the giant rolls to pieces a trifle larger than a man's head in a few seconds. After leaving the giant rolls the broken rock passed on through other crushing-rolls of somewhat similar construction. These also were invented by Edison, but antedated those previously described; being covered by Patent No. 567,187, issued September 8, 1896. These rolls were intended for the reducing of "one-man-size" rocks to small pieces, which at the time of their original inception was about the standard size of similar machines. At the Edison concentrating plant the broken rock, after passing through these rolls, was further reduced in size by other rolls, and was then ready to be crushed to a fine powder through the medium of another remarkable machine devised by Edison to meet his ever-recurring and well-defined ideas of the utmost economy and efficiency. NOTE.--Figs. 3 and 4 are reproduced from similar sketches on pages 84 and 85 of McClure's Magazine for November, 1897, by permission of S. S. McClure Co. The best fine grinding-machines that it was then possible to obtain were so inefficient as to involve a loss of 82 per cent. of the power applied. The thought of such an enormous loss was unbearable, and he did not rest until he had invented and put into use an entirely new grinding-machine, which was called the "three-high" rolls. The device was covered by a patent issued to him on November 21, 1899, No. 637,327. It was a most noteworthy invention, for it brought into the art not only a greater efficiency of grinding than had ever been dreamed of before, but also a tremendous economy by the saving of power; for whereas the previous efficiency had been 18 per cent. and the loss 82 per cent., Edison reversed these figures, and in his three-high rolls produced a working efficiency of 84 per cent., thus reducing the loss of power by friction to 16 per cent. A diagrammatic sketch of this remarkable machine is shown in Fig. 5, which shows a front elevation with the casings, hopper, etc., removed, and also shows above the rolls the rope and pulleys, the supports for which are also removed for the sake of clearness in the illustration. For the convenience of the reader, in referring to Fig. 5, we will repeat the description of the three-high rolls, which is given on pages 487 and 488 of the preceding narrative. In the two end-pieces of a heavy iron frame were set three rolls, or cylinders--one in the centre, another below, and the other above--all three being in a vertical line. These rolls were about three feet in diameter, made of cast-iron, and had face-plates of chilled-iron. [31] The lowest roll was set in a fixed bearing at the bottom of the frame, and, therefore, could only turn around on its axis. The middle and top rolls were free to move up or down from and toward the lower roll, and the shafts of the middle and upper rolls were set in a loose bearing which could slip up and down in the iron frame. It will be apparent, therefore, that any material which passed in between the top and the middle rolls, and the middle and bottom rolls, could be ground as fine as might be desired, depending entirely upon the amount of pressure applied to the loose rolls. In operation the material passed first through the upper and middle rolls, and then between the middle and lowest rolls. [Footnote 31: The faces of these rolls were smooth, but as three-high rolls came into use later in Edison's Portland cement operations the faces were corrugated so as to fit into each other, gear-fashion, to provide for a high rate of feed] This pressure was applied in a most ingenious manner. On the ends of the shafts of the bottom and top rolls there were cylindrical sleeves, or bearings, having seven sheaves in which was run a half-inch endless wire rope. This rope was wound seven times over the sheaves as above, and led upward and over a single-groove sheave, which was operated by the piston of an air-cylinder, and in this manner the pressure was applied to the rolls. It will be seen, therefore that the system consisted in a single rope passed over sheaves and so arranged that it could be varied in length, thus providing for elasticity in exerting pressure and regulating it as desired. The efficiency of this system was incomparably greater than that of any other known crusher or grinder, for while a pressure of one hundred and twenty-five thousand pounds could be exerted by these rolls, friction was almost entirely eliminated, because the upper and lower roll bearings turned with the rolls and revolved in the wire rope, which constituted the bearing proper. Several other important patents have been issued to Edison for crushing and grinding rolls, some of them being for elaborations and improvements of those above described but all covering methods of greater economy and effectiveness in rock-grinding. Edison's work on conveyors during the period of his ore-concentrating labors was distinctively original, ingenious and far in advance of the times. His conception of the concentrating problem was broad and embraced an entire system, of which a principal item was the continuous transfer of enormous quantities of material from place to place at the lowest possible cost. As he contemplated the concentration of six thousand tons daily, the expense of manual labor to move such an immense quantity of rock, sand, and ore would be absolutely prohibitive. Hence, it became necessary to invent a system of conveyors that would be capable of transferring this mass of material from one place to another. And not only must these conveyors be capable of carrying the material, but they must also be devised so that they would automatically receive and discharge their respective loads at appointed places. Edison's ingenuity, engineering ability, and inventive skill were equal to the task, however, and were displayed in a system and variety of conveyors that in practice seemed to act with almost human discrimination. When fully installed throughout the plant, they automatically transferred daily a mass of material equal to about one hundred thousand cubic feet, from mill to mill, covering about a mile in the transit. Up and down, winding in and out, turning corners, delivering material from one to another, making a number of loops in the drying-oven, filling up bins and passing on to the next when they were full, these conveyors in automatic action seemingly played their part with human intelligence, which was in reality the reflection of the intelligence and ingenuity that had originally devised them and set them in motion. Six of Edison's patents on conveyors include a variety of devices that have since came into broad general use for similar work, and have been the means of effecting great economies in numerous industries of widely varying kinds. Interesting as they are, however, we shall not attempt to describe them in detail, as the space required would be too great. They are specified in the list of patents following this Appendix, and may be examined in detail by any interested student. In the same list will also be found a large number of Edison's patents on apparatus and methods of screening, drying, mixing, and briquetting, as well as for dust-proof bearings, and various types and groupings of separators, all of which were called forth by the exigencies and magnitude of his great undertaking, and without which he could not possibly have attained the successful physical results that crowned his labors. Edison's persistence in reducing the cost of his operations is noteworthy in connection with his screening and drying inventions, in which the utmost advantage is taken of the law of gravitation. With its assistance, which cost nothing, these operations were performed perfectly. It was only necessary to deliver the material at the top of the chambers, and during its natural descent it was screened or dried as the case might be. All these inventions and devices, as well as those described in detail above (except magnetic separators and mixing and briquetting machines), are being used by him to-day in the manufacture of Portland cement, as that industry presents many of the identical problems which presented themselves in relation to the concentration of iron ore. XVII. THE LONG CEMENT KILN IN this remarkable invention, which has brought about a striking innovation in a long-established business, we see another characteristic instance of Edison's incisive reasoning and boldness of conception carried into practical effect in face of universal opinions to the contrary. For the information of those unacquainted with the process of manufacturing Portland cement, it may be stated that the material consists preliminarily of an intimate mixture of cement rock and limestone, ground to a very fine powder. This powder is technically known in the trade as "chalk," and is fed into rotary kilns and "burned"; that is to say, it is subjected to a high degree of heat obtained by the combustion of pulverized coal, which is injected into the interior of the kiln. This combustion effects a chemical decomposition of the chalk, and causes it to assume a plastic consistency and to collect together in the form of small spherical balls, which are known as "clinker." Kilns are usually arranged with a slight incline, at the upper end of which the chalk is fed in and gradually works its way down to the interior flame of burning fuel at the other end. When it arrives at the lower end, the material has been "burned," and the clinker drops out into a receiving chamber below. The operation is continuous, a constant supply of chalk passing in at one end of the kiln and a continuous dribble of clinker-balls dropping out at the other. After cooling, the clinker is ground into very fine powder, which is the Portland cement of commerce. It is self-evident that an ideal kiln would be one that produced the maximum quantity of thoroughly clinkered material with a minimum amount of fuel, labor, and investment. When Edison was preparing to go into the cement business, he looked the ground over thoroughly, and, after considerable investigation and experiment, came to the conclusion that prevailing conditions as to kilns were far from ideal. The standard kilns then in use were about sixty feet in length, with an internal diameter of about five feet. In all rotary kilns for burning cement, the true clinkering operation takes place only within a limited portion of their total length, where the heat is greatest; hence the interior of the kiln may be considered as being divided longitudinally into two parts or zones--namely, the combustion, or clinkering, zone, and the zone of oncoming raw material. In the sixty-foot kiln the length of the combustion zone was about ten feet, extending from a point six or eight feet from the lower, or discharge, end to a point about eighteen feet from that end. Consequently, beyond that point there was a zone of only about forty feet, through which the heated gases passed and came in contact with the oncoming material, which was in movement down toward the clinkering zone. Since the bulk of oncoming material was small, the gases were not called upon to part with much of their heat, and therefore passed on up the stack at very high temperatures, ranging from 1500 degrees to 1800 degrees Fahr. Obviously, this heat was entirely lost. An additional loss of efficiency arose from the fact that the material moved so rapidly toward the combustion zone that it had not given up all its carbon dioxide on reaching there; and by the giving off of large quantities of that gas within the combustion zone, perfect and economical combustion of coal could not be effected. The comparatively short length of the sixty-foot kiln not only limited the amount of material that could be fed into it, but the limitation in length of the combustion zone militated against a thorough clinkering of the material, this operation being one in which the elements of time and proper heat are prime considerations. Thus the quantity of good clinker obtainable was unfavorably affected. By reason of these and other limitations and losses, it had been possible, in practice, to obtain only about two hundred and fifty barrels of clinker per day of twenty-four hours; and that with an expenditure for coal proportionately equal to about 29 to 33 per cent. of the quantity of clinker produced, even assuming that all the clinker was of good quality. Edison realized that the secret of greater commercial efficiency and improvement of quality lay in the ability to handle larger quantities of material within a given time, and to produce a more perfect product without increasing cost or investment in proportion. His reasoning led him to the conclusion that this result could only be obtained through the use of a kiln of comparatively great length, and his investigations and experiments enabled him to decide upon a length of one hundred and fifty feet, but with an increase in diameter of only six inches to a foot over that of the sixty-foot kiln. The principal considerations that influenced Edison in making this radical innovation may be briefly stated as follows: First. The ability to maintain in the kiln a load from five to seven times greater than ordinarily employed, thereby tending to a more economical output. Second. The combustion of a vastly increased bulk of pulverized coal and a greatly enlarged combustion zone, extending about forty feet longitudinally into the kiln--thus providing an area within which the material might be maintained in a clinkering temperature for a sufficiently long period to insure its being thoroughly clinkered from periphery to centre. Third. By reason of such a greatly extended length of the zone of oncoming material (and consequently much greater bulk), the gases and other products of combustion would be cooled sufficiently between the combustion zone and the stack so as to leave the kiln at a comparatively low temperature. Besides, the oncoming material would thus be gradually raised in temperature instead of being heated abruptly, as in the shorter kilns. Fourth. The material having thus been greatly raised in temperature before reaching the combustion zone would have parted with substantially all its carbon dioxide, and therefore would not introduce into the combustion zone sufficient of that gas to disturb the perfect character of the combustion. Fifth. On account of the great weight of the heavy load in a long kiln, there would result the formation of a continuous plastic coating on that portion of the inner surface of the kiln where temperatures are highest. This would effectively protect the fire-brick lining from the destructive effects of the heat. Such, in brief, were the essential principles upon which Edison based his conception and invention of the long kiln, which has since become so well known in the cement business. Many other considerations of a minor and mechanical nature, but which were important factors in his solution of this difficult problem, are worthy of study by those intimately associated with or interested in the art. Not the least of the mechanical questions was settled by Edison's decision to make this tremendously long kiln in sections of cast-iron, with flanges, bolted together, and supported on rollers rotated by electric motors. Longitudinal expansion and thrust were also important factors to be provided for, as well as special devices to prevent the packing of the mass of material as it passed in and out of the kiln. Special provision was also made for injecting streams of pulverized coal in such manner as to create the largely extended zone of combustion. As to the details of these and many other ingenious devices, we must refer the curious reader to the patents, as it is merely intended in these pages to indicate in a brief manner the main principles of Edison's notable inventions. The principal United States patent on the long kiln was issued October 24, 1905, No. 802,631. That his reasonings and deductions were correct in this case have been indubitably proven by some years of experience with the long kiln in its ability to produce from eight hundred to one thousand barrels of good clinker every twenty-four hours, with an expenditure for coal proportionately equal to about only 20 per cent. of the quantity of clinker produced. To illustrate the long cement kiln by diagram would convey but little to the lay mind, and we therefore present an illustration (Fig. 1) of actual kilns in perspective, from which sense of their proportions may be gathered. XVIII. EDISON'S NEW STORAGE BATTERY GENERICALLY considered, a "battery" is a device which generates electric current. There are two distinct species of battery, one being known as "primary," and the other as "storage," although the latter is sometimes referred to as a "secondary battery" or "accumulator." Every type of each of these two species is essentially alike in its general make-up; that is to say, every cell of battery of any kind contains at least two elements of different nature immersed in a more or less liquid electrolyte of chemical character. On closing the circuit of a primary battery an electric current is generated by reason of the chemical action which is set up between the electrolyte and the elements. This involves a gradual consumption of one of the elements and a corresponding exhaustion of the active properties of the electrolyte. By reason of this, both the element and the electrolyte that have been used up must be renewed from time to time, in order to obtain a continued supply of electric current. The storage battery also generates electric current through chemical action, but without involving the constant repriming with active materials to replace those consumed and exhausted as above mentioned. The term "storage," as applied to this species of battery, is, however, a misnomer, and has been the cause of much misunderstanding to nontechnical persons. To the lay mind a "storage" battery presents itself in the aspect of a device in which electric energy is STORED, just as compressed air is stored or accumulated in a tank. This view, however, is not in accordance with facts. It is exactly like the primary battery in the fundamental circumstance that its ability for generating electric current depends upon chemical action. In strict terminology it is a "reversible" battery, as will be quite obvious if we glance briefly at its philosophy. When a storage battery is "charged," by having an electric current passed through it, the electric energy produces a chemical effect, adding oxygen to the positive plate, and taking oxygen away from the negative plate. Thus, the positive plate becomes oxidized, and the negative plate reduced. After the charging operation is concluded the battery is ready for use, and upon its circuit being closed through a translating device, such as a lamp or motor, a reversion ("discharge") takes place, the positive plate giving up its oxygen, and the negative plate being oxidized. These chemical actions result in the generation of an electric current as in a primary battery. As a matter of fact, the chemical actions and reactions in a storage battery are much more complex, but the above will serve to afford the lay reader a rather simple idea of the general result arrived at through the chemical activity referred to. The storage battery, as a commercial article, was introduced into the market in the year 1881. At that time, and all through the succeeding years, until about 1905, there was only one type that was recognized as commercially practicable--namely, that known as the lead-sulphuric-acid cell, consisting of lead plates immersed in an electrolyte of dilute sulphuric acid. In the year last named Edison first brought out his new form of nickel-iron cell with alkaline electrolyte, as we have related in the preceding narrative. Early in the eighties, at Menlo Park, he had given much thought to the lead type of storage battery, and during the course of three years had made a prodigious number of experiments in the direction of improving it, probably performing more experiments in that time than the aggregate of those of all other investigators. Even in those early days he arrived at the conclusion that the lead-sulphuric-acid combination was intrinsically wrong, and did not embrace the elements of a permanent commercial device. He did not at that time, however, engage in a serious search for another form of storage battery, being tremendously occupied with his lighting system and other matters. It may here be noted, for the information of the lay reader, that the lead-acid type of storage battery consists of two or more lead plates immersed in dilute sulphuric acid and contained in a receptacle of glass, hard rubber, or other special material not acted upon by acid. The plates are prepared and "formed" in various ways, and the chemical actions are similar to those above stated, the positive plate being oxidized and the negative reduced during "charge," and reversed during "discharge." This type of cell, however, has many serious disadvantages inherent to its very nature. We will name a few of them briefly. Constant dropping of fine particles of active material often causes short-circuiting of the plates, and always necessitates occasional washing out of cells; deterioration through "sulphation" if discharge is continued too far or if recharging is not commenced quickly enough; destruction of adjacent metalwork by the corrosive fumes given out during charge and discharge; the tendency of lead plates to "buckle" under certain conditions; the limitation to the use of glass, hard rubber, or similar containers on account of the action of the acid; and the immense weight for electrical capacity. The tremendously complex nature of the chemical reactions which take place in the lead-acid storage battery also renders it an easy prey to many troublesome diseases. In the year 1900, when Edison undertook to invent a storage battery, he declared it should be a new type into which neither sulphuric nor any other acid should enter. He said that the intimate and continued companionship of an acid and a metal was unnatural, and incompatible with the idea of durability and simplicity. He furthermore stated that lead was an unmechanical metal for a battery, being heavy and lacking stability and elasticity, and that as most metals were unaffected by alkaline solutions, he was going to experiment in that direction. The soundness of his reasoning is amply justified by the perfection of results obtained in the new type of storage battery bearing his name, and now to be described. The essential technical details of this battery are fully described in an article written by one of Edison's laboratory staff, Walter E. Holland, who for many years has been closely identified with the inventor's work on this cell The article was published in the Electrical World, New York, April 28, 1910; and the following extracts therefrom will afford an intelligent comprehension of this invention: "The 'A' type Edison cell is the outcome of nine years of costly experimentation and persistent toil on the part of its inventor and his associates.... "The Edison invention involves the use of an entirely new voltaic combination in an alkaline electrolyte, in place of the lead-lead-peroxide combination and acid electrolyte, characteristic of all other commercial storage batteries. Experience has proven that this not only secures durability and greater output per unit-weight of battery, but in addition there is eliminated a long list of troubles and diseases inherent in the lead-acid combination.... "The principle on which the action of this new battery is based is the oxidation and reduction of metals in an electrolyte which does not combine with, and will not dissolve, either the metals or their oxides; and an electrolyte, furthermore, which, although decomposed by the action of the battery, is immediately re-formed in equal quantity; and therefore in effect is a CONSTANT element, not changing in density or in conductivity. "A battery embodying this basic principle will have features of great value where lightness and durability are desiderata. For instance, the electrolyte, being a constant factor, as explained, is not required in any fixed and large amount, as is the case with sulphuric acid in the lead battery; thus the cell may be designed with minimum distancing of plates and with the greatest economy of space that is consistent with safe insulation and good mechanical design. Again, the active materials of the electrodes being insoluble in, and absolutely unaffected by, the electrolyte, are not liable to any sort of chemical deterioration by action of the electrolyte--no matter how long continued.... "The electrolyte of the Edison battery is a 21 per cent. solution of potassium hydrate having, in addition, a small amount of lithium hydrate. The active metals of the electrodes--which will oxidize and reduce in this electrolyte without dissolution or chemical deterioration--are nickel and iron. These active elements are not put in the plates AS METALS; but one, nickel, in the form of a hydrate, and the other, iron, as an oxide. "The containing cases of both kinds of active material (Fig. 1), and their supporting grids (Fig. 2), as well as the bolts, washers, and nuts used in assembling (Fig. 3), and even the retaining can and its cover (Fig. 4), are all made of nickel-plated steel--a material in which lightness, durability and mechanical strength are most happily combined, and a material beyond suspicion as to corrosion in an alkaline electrolyte.... "An essential part of Edison's discovery of active masetials for an alkaline storage battery was the PREPARATION of these materials. Metallic powder of iron and nickel, or even oxides of these metals, prepared in the ordinary way, are not chemically active in a sufficient degree to work in a battery. It is only when specially prepared iron oxide of exceeding fineness, and nickel hydrate conforming to certain physical, as well as chemical, standards can be made that the alkaline battery is practicable. Needless to say, the working out of the conditions and processes of manufacture of the materials has involved great ingenuity and endless experimentation." The article then treats of Edison's investigations into means for supporting and making electrical connection with the active materials, showing some of the difficulties encountered and the various discoveries made in developing the perfected cell, after which the writer continues his description of the "A" type cell, as follows: "It will be seen at once that the construction of the two kinds of plate is radically different. The negative or iron plate (Fig. 5) has the familiar flat-pocket construction. Each negative contains twenty-four pockets--a pocket being 1/2 inch wide by 3 inches long, and having a maximum thickness of a little more than 1/8 inch. The positive or nickel plate (Fig. 6) is seen to consist of two rows of round rods or pencils, thirty in number, held in a vertical position by a steel support-frame. The pencils have flat flanges at the ends (formed by closing in the metal case), by which they are supported and electrical connection is made. The frame is slit at the inner horizontal edges, and then folded in such a way as to make individual clamping-jaws for each end-flange. The clamping-in is done at great pressure, and the resultant plate has great rigidity and strength. "The perforated tubes into which the nickel active material is loaded are made of nickel-plated steel of high quality. They are put together with a double-lapped spiral seam to give expansion-resisting qualities, and as an additional precaution small metal rings are slipped on the outside. Each tube is 1/4 inch in diameter by 4 1/8 inches long, add has eight of the reinforcing rings. "It will be seen that the 'A' positive plate has been given the theoretically best design to prevent expansion and overcome trouble from that cause. Actual tests, long continued under very severe conditions, have shown that the construction is right, and fulfils the most sanguine expectations." Mr. Holland in his article then goes on to explain the development of the nickel flakes as the conducting factor in the positive element, but as this has already been described in Chapter XXII, we shall pass on to a later point, where he says: "An idea of the conditions inside a loaded tube can best be had by microscopic examination. Fig. 7 shows a magnified section of a regularly loaded tube which has been sawed lengthwise. The vertical bounding walls are edges of the perforated metal containing tube; the dark horizontal lines are layers of nickel flake, while the light-colored thicker layers represent the nickel hydrate. It should be noted that the layers of flake nickel extend practically unbroken across the tube and make contact with the metal wall at both sides. These metal layers conduct current to or from the active nickel hydrate in all parts of the tube very efficiently. There are about three hundred and fifty layers of each kind of material in a 4 1/8-inch tube, each layer of nickel hydrate being about 0.01 inch thick; so it will be seen that the current does not have to penetrate very far into the nickel hydrate--one-half a layer's thickness being the maximum distance. The perforations of the containing tube, through which the electrolyte reaches the active material, are also shown in Fig. 7." In conclusion, the article enumerates the chief characteristics of the Edison storage battery which fit it preeminently for transportation service, as follows: 1. No loss of active material, hence no sediment short-circuits. 2. No jar breakage. 3. Possibility of quick disconnection or replacement of any cell without employment of skilled labor. 4. Impossibility of "buckling" and harmlessness of a dead short-circuit. 5. Simplicity of care required. 6. Durability of materials and construction. 7. Impossibility of "sulphation." 8. Entire absence of corrosive fumes. 9. Commercial advantages of light weight.