[PT031AAP1], Technical Note, Thomas Alva Edison, October 21st, 1887
[PT031AAP1], Technical Note, Thomas Alva Edison, October 21st, 1887
Caveat The object of this invention is to reproduce or multiply copies of phonographic Records called phonograms The following is a record of experiments tried, being tried and untried. After the cylinder or plate is covered with wax or similar material is indented by the action of the voice, The cylinder is placed in a vacuum chamber containing two electrodes of Gold or other unoxidizable metal and an arc being formed by brining the points together & seperating the same the electric current causes the metal of the points to be vaporized & this is deposited in a perfect manner over the whole surface of the cylinder The latter if necessary is rotated while being deposited on by clockwork in the vacuum-- Thus the non conducting surface is perfectly coated with a conducting surface more perfect than by any other means, it is then taken out of the vacuum chamber placed in a mould & backed up by either Type metal or plaster of paris or it may be placed in a plating Batch & the deposit may be increased to a 1/4 of an inch with Copper nickel etc in the usual manner-- When so prepared the mould is cut in 3 parts by an exceedingly thin saw it is jointed with hinges so that when closed it will come accurately together, the space left by the saw being replaced by a strip of metal, the loss of 2 or 3 indentations is not noticeable to the ear-- after this is done the cylinders may be reproduced by Type metal, plaster paris, sealing wax under a slight pressure, while soft, Gums resins, oxychloride Zinc, Chloride & oxide Magnesia, Thick polished tin foil placed in the cylinder against the inner face & then poured with a semi solid like putty Viscous Tar or pieces of Rubber, Gutta percha etc & the whole subjectd to pressure which forces the foil into the indentation over the whole surface thus reproducing the record-- on removing the semi solids, plaster paris may be poured in to back up the foil-- The cylinder opened the record taken out and the process gone over again to preoduce a second cylinder-- If the cylinder reproduced has a a plaster of Paris face, the cutting quality of the surface which tents to produced scratching & wearing away of the point may be modified & reduced by dipping in a thin solution of a gum or wax in a volitile solvent, like parafine in Benzol etc, or Gelatine fish glue Tragacanth, in water, gutta percha-- in chloroform or flexible collodion It is even possible to take a cylinder of very hard wax and raising its termperature to a certain point it is recorded upon when it cools it hardens very materially & this cylinder may be used to reproduce on the surface of a similar cyliner covered with a hard wax softened by heat, The indenting cylinder being kept cool-- If the two cylinders are placed on rotating shafts & the two surfaces be brought accurately together with considerable pressure, a single rotation will perfectly transfer the record of one to the other. This second cylinder may itself be used to reproduce the record audably but it is preferbly used to indent a great number of cylindrs thus reproducting the records almost indefinitely The recorded cylinder may have its surface covered with plumbago so as to cause it to become an electrical conductor and this placed in a plating bath & covered as thickly as requied by coper or other plateable metal. But in this case it is essential to add one feature to ensure perfect results which feature is new & that is the graphite always used by electrotypers must be ground very much finer than now used otherwise the particles of graphite are themselves in many cases as large if not larger than many of the indentations due to speaking especially in the hissing sounds & overtones of stringed instruments, but the graphite may be ground so fine that this defect will not arrise & almost perfect surface is obtained but it is never so perfect & accurate as that due to electro vacuous deposits On hard way cylinders recorded upon while softened by a rise of temperature, Tin foil very thin polished is then placed over the entire surface-- over this again is poured plaster paris, after setting the wax is melted or dissolved out by its proper solvent The mould is then split in 2 or more sections & the Molten Waxes gums Bitumenous Soap-- setting compounds etc can be run in-- The cylinder or plate having a wax surface is made of several pieces of thin paper straw paper for instance wound on a mandrel to the proper size the end being fastened by glue Tragacanth, Gum or adhesive substance not effected by the hot wax or any solvent thereof. To insure a clean smooth inner surfact to each phonogram so it will register accurately & pass on the holder in the phonograph properly I take a sheet of smooth material for instance hand callendered card board-- of such as size that will just wrap around the mandrel & the two ends butt together, over this the body of the phonogram is wound of the coarse quality paper. Thus when the paper phonogram is pulled off the mandril it has a smooth inner surface;-- This inner sheet may have the surface which goes over the mandril coated with a smooth surface of varnish Asphalt for instance or shellac after the ends of the cylinder so formed is cut off by a cutter, (the mandril having 2 grooves in it at each end of the cylinder the whole is pulled off and the another cylinder may be formed-- Another metho of forming cylinders is to have a mould in which plaster pairs, Lime & water glass, Oxide of Zinc & Chloride Magnesia, or other setting material may be poured this forming the hollow cylindrical shell ready for putting in the thin wax surface for recording This mould may be greatly strengthened and powders such as Earthy Oxides mixed with tar, or asphalt may be forced into the mould when softened by heat & cylinders produced by this method. Where the cylinders are to be very light, Light porous bodies like Lampblack Charcoal Cork may be mixed with powdered Asphalt, Pitch or other mateiral which will soften by a gentle heat & thus the whole be forced into the mould the Asphalts etc hardening immediately as the Temperature drops binds the whole together; The cylinders may even be formed of a hard wax or asphalt itself-- & afterwards surfaced with the softer material for recording-- Another method of forming plates or shells is the use of the Lead pipe press whereby compounds softened by heat such as asphalts mixed with various inert substances like brick ducst Chalk, Lime etc may be squirted out with great rapidity & be remarkably smooth & acurate. Paper or wood or straw board pulp mixed with gums, Bitumenous in a soluable or viscous condition, glue, may be softened by heat making a plastic mass the temperature not rising high enough to char the pulp; can be squirted through the Lead pipe press in any required form the sufrace afterwards being waxed to receive the record. Boric acid may be squirted into cylinders or plates when the proper heat is applied the whole being waxed to prevent the action of the atmosphere even glass itself may be squirted in this manner a special glass having an excess of alkali & Lead oxide rendering it extremely fusible It is essential to transmit phonogram cylinders by mail, if these are made of fraible sustances they are very liable to be crushed, indented or otherwise injured in tranist. Cylinders of a slightly increased size may be used made of Lime & Asphalt moulded hot will stand a great pressure & thus preserve the enclosed phonogram from injury. Metllic phonogram shells say of Zinc, Type metal or brass tubing, may be used in many cases. Shalls may be turned out of wood. Sawdust mixed with binding substances can be moulded or pressed.
Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University