The Edison Battery.

Progress, Volume III, Issue 4, 1 February 1908, Page 126

The Edison Battery.

The daily press has again been concerned as to the latest magical discovery of Mr. Edison. The long-promised tattery — which is to revolutionise the motor-car industry, consign all petrol vehicles to the scrap heap, create a boom in aeroplanes and flying machines, and relegate the horse to the limited sphere of a zoological exhibit or domestic ornament, and so on — is about to be presented to the world at large. To the general public these announcements, exaggerated though they may be, are good reading, and as such sufficient ; but the engineer requires facts and details. A recent issue of the Electrical World contained some extracts from the many patents recently taken out by Mr. Edison in connection with his development of the new storage battery. The series of patents reveals a remarkable perfection of detail in experimental work, and affords testimony as to the sustained ingenuity of the inventor. One of the patents covers a method of making seamless steel battery boxes or cans. The manufacture of these seamless steel vessels is effected by means of electrolytic deposition in a number of steps, each of which is important and essential to the success of the process. Hollow brass or copper moulds of the proper form are first coated with an exceedingly thin layer of paraffin wax, over which a coating of graphite is applied. The layer of wax is so thin that the graphite apparently makes contact through the wax with the mould. A coating of copper of about 0.004 in. in thickness is then applied electrolytically. The mould is then removed, washed, and introduced into a second tank, where it receives an electrolytic coating of nickel about 0.001 in. thick. Then it passes into a third tank containing a neutral ferrous ammonium sulphate solution with iron anodes. Here it receives an iron coatmg of about 0.02 in. thickness. In order to prevent the formation of pits or holes in the deposited iron coating, which would be likely to form by the accumulation of gas bubbles thereon, and in order to secure a very smooth surface, a quantity of crushed charcoal is introduced into the solution, whereby the added material will rub over and scour the surface of the deposited metal, polish the same and wipe off any gas bubbles which may tend to accumulate. During the ironplating the mould is rapidly revolved at a speed of about l\ r.p.s. The mould is then removed from the tank and washed in water of a temperature of about 76 deg. C, thereby melting the wax originally deposited on the mould. The deposited can is then removed

from the mould and is annealed by heating it to red heat in a closed retort containing a non-oxidising atmosphere, such as hydrogen gas. After annealing, the articles are allowed to cool in the same atmosphere. Finally, the copper originally deposited on the graphite is removed by filling the can with a solution of copper nitrate and sodium nitrate and using the can as an anode against a copper cathode. It is quite evident that in this long process, which is, of course carried ont by automatic machinery, not a single step is superfluous. The wax coating on the mould is applied to permit later an easy removal of the deposited can from the mould. The graphite coat serves for making the surface conductive. The copper coat is necessary because a nickel deposit would not stick to the graphite. The nickel is necessary on account of the caustic soda electrolyte of the battery. In depositing the iron, the use of the small particles of crushed charcoal not only serves for wiping off the gas-bubbles, but also for incorporating a small percentage of carbon with the iron. In the subsequent annealing process the iron gets the necessary strength, and on account of the small percentage of carbon incorporated with it, it is, in fact, converted into a superior product of soft steel containing almost 0.4 per cent, of carbon. It was early recognised by Mr. Edison that in order to get high conductivity of the active mass m the little pockets of his storage battery plates, it was necessary to mix the active mass of nickel hydroxide with some material of good conductivity. Flake graphite was first used, but in the course of a long time it was found that the flake graphite undergoes a change in its contact resistance, and the capacity of the battery is thereby diminished. Mr. Edison now uses flakes of a nickel-cobalt alloy, containing, say, 60 per cent, of cobalt, and 40 per cent, of nickel. Of the numerous patents for the production of these flakes or films it will be sufficient to describe the method revealed in the last patent. A copper cylinder with a polished nickel-plated surface is first immersed in a suitable cobalt plating bath, and while the cathode is revolved a thin film of cobalt 0.0001 in. or less in thickness is plated on the cathode. This is then washed and placed in a solution of copper sulphate containing some free acid, whereby the cobalt is caused to go into solution, and the copper is deposited as cement copper in granular, but slightly adhesive, form. The cylinder is then placed in a copper plating bath and an electro deposit of copper 0.003 in. to 0.0035 in. thick is obtained on the cement copper, while the cathode is rotated. It is then washed and introduced into a bath consisting of a mixture of chloride of cobalt and chloride of nickel, and a cobalt-nickel alloy deposit is obtained about 0.0002 in. thick. The cylinder is again washed and a second film of copper is deposited, then another film of cobalt nickel, and so on, producing electrolytically alternating layers of copper and cobaltnickel, until a composite sheet of sufficient thickness has been obtained. This sheet is cut longitudinally off the cathode mto small strips which are placed in a basket and introduced into an ammoniacal solution of copper sulphate and moved up and down in this bath. The copper is thereby dissolved, while the nickel and cobalt zse not attacked, so that the desired films or flakes of cobalt nickel are obtained.