and the manner of securing perfect contact between it and the leading wires. The specification continued with a statement of what had been previously attempted in the same direction. Rods of carbon had been used of from one to four ohms' resistance, in glass vessels with a gas incapable of combining with carbon, the glass being cemented to a metallic base, and the rods clamped to the leading wires. The necessity for high resistance in the lamp compared to the rest of the circuit was pointed out, necessitating with such rods large conductors and consequent impossibility of keeping the globes air-tight. When a non-combining gas was used in the globe at atmospheric pressure, "air-washing" or attrition was produced by the passage of gas over the heated carbon. The specification continued: "I have reversed this practice. I have discovered that even a cotton thread properly carbonized and placed in a sealed glass bulb exhausted to onemillionth of an atmosphere offers from one hundred to five hundred ohms' resistance to the passage of the current, and that it is absolutely stable at very high temperatures; that if the thread be coiled as a spiral and carbonized, or if any fibrous vegetable substance which will leave a carbon residue after heating in a closed chamber be so coiled, that as much as two thousand ohms' resistance may be obtained without presenting a radiating surface greater than three-sixteenths of an inch; that if such fibrous material be rubbed with a plastic compound composed of lamp-black and tar, its resistance may be made high or low according to the amount of lamp-black placed upon it. I have also discovered that carbon filaments may be made by a combination of tar and lamp-black, the latter being previously ignited in a closed crucible for several hours and afterwards moistened and kneaded until it assumes the consistency of thick putty. Small pieces of this material may be rolled out in the form of wire as small as seven one-thousandths (100) of an inch in diameter, and over a foot in length, and the same may be coated with a non-conducting non-carbonizable substance and wound on a bobbin, or as a spiral, and the tar carbonized in a closed chamber by subjecting it to high heat, the spiral after carbonization retaining its form. I sometimes roll a thread within the compound of lamp-black and tar, so as to allow of greater convenience in handling the same, and the flexible carbon filament is not so liable to crack by its own weight in the act of winding. "To increase the resistance of the compound of lamp-black and tar, I sometimes work into it a volatile powder, such as powdered camphor, oxide zinc, but to make the light insensitive to variations of the current a considerable mass of matter should be used, in order that the specific heat ot the lamp may be increased so that it takes a long time to reach its full brilliancy and also to die away slowly. "To do this it is better to have the carbon as homogeneous as possible, and obtain the requisite resistance by employing a filament several inches long and winding the same in a spiral form, so that the external radiating surface shall be small. All these forms are fragile, and cannot be clamped to the leading wires with sufficient force to ensure good contact and prevent heating. I have discovered that if platinum wires are used and the plastic lamp-black and tar material be molded around it, that in the act of carbonization there is an intimate union by combination and by pressure between the carbon and platina, and nearly perfect contact is obtained without the necessity of clamps, hence the light-giving body, and the platina wires are connected and ready to be placed in the vacuum bulb. "When fibrous material is used the plastic lamp-black and tar is employed to secure it to the platina wires before carbonizing. By using the carbon wire of such high resistance, I am enabled to use fine platinum wires for leading wires, as they will have a small resistance compared to the light-giving body, hence will not heat and crack the sealed vacuum bulb. "Platina can only be used, as its expansion is nearly the same as that of glass. By using a considerable length of carbon wire and coiling it in such a manner that only a small portion of its entire surface radiates light, I can raise the specific heat of the whole, and thus prevent the rapid reception and disappearance of the light, which on a plain wire is prejudicial, as it shows the least unsteadiness of the current by the flickering of the light, but if the current is steady, the defect does not show. I have carbonized and used cotton and linen thread, wood splints, paper coiled in various ways; also lamp-black plumbago and carbon in various forms mixed with tar and kneaded so that the same may be rolled out into wires of various lengths and diameters; each wire, however, is to be uniform in size throughout. If the carbon thread is liable to be distorted during carbonization, it is to be coiled between a helix of copper wire. The ends of the carbon or filament are secured to the platina leading wires by plastic carbonizable material, and the whole placed in the carbonizing chamber." The copper was to be subsequently removed by nitric acid, the bulb exhausted and hermetically sealed at a high vacuum. Substances not easily distorted in carbonizing might be coated with some non-conductor, so allowing the coils to rest on each other. In the drawings Fig. 1 is a section of the lamp, Fig. 2 the plastic material before being wound into a spiral, Fig. 3 the spiral after carbonization; a is the filament, c, c' its thickened ends, d the platinum wires, h the connecting clamps, the leading wires sealed in the glass, m the tube to the vacuum pump, and e the outer conductors. The claims were "First, an electric lamp for giving light by incandescence consisting of a filament of carbon of high resistance, made as described and secured to metallic wires as set forth. "Second, the combination of a carbon filament within a receiver made entirely of glass, through which the leading wires pass, and from which receiver the air is exhausted for the purposes set forth. "Third, a coiled carbon filament or strip arranged in such a manner that only a portion of the surface of such carbon conductor shall radiate light as set forth. "Fourth, the method herein described of securing the platina contact wires to the carbon filament and carbonizing of the whole in a closed chamber, substantially as set forth." At the trial of the action for infringement of this patent a large number of anticipations were alleged; in some the conductors were not of carbon, in others carbon rods were used, being filed or otherwise made thin. It was proved that the conditions for success were well known, viz. that the heating of the circuit was developed in proportion to the resistance of each part, hence that of the incandescent part of the lamp must be relatively very great; that the resistance of each part depended on its material, and was proportional to its length and inversely as its cross-section; that the lighting effected depended also upon the specific heat of the conductor; and that carbon enclosed in a vacuum was an excellent material to use. fire was no evidence that any successful lamp had previously been made except two made and exhibited by Mr. Swan. These had a straight carbon rod as conductor, between platinum wires hermetically sealed in the glass, which was exhausted so that it was practically a vacuum. The rod was not fine enough to be a "filament;" it bent owing to expansion, and broke down after some time. The chief objections were raised to the second claim, and it was contended (1) That it was too wide if it included conductors other than those described in the body of the specification. (2) That there was no sufficient description of what thickness or thinness constituted a "filament." (3) That the invention was the use of old things in a known way, and that the mere alteration in size was not "invention." The learned judge decided all points in the plaintiff's favour (3 R. P. C. 167). Held, on appeal by the Court of Appeal (Cotton, L.J., dissenting)- That the second claim was for a combination consisting of five elements : (1) a carbon conductor, (2) in the form of a filament, (3) a receiver wholly of glass, (4) a vacuum, and (5) the entrance of leading wires through the glass. That the third and fourth claims were for the other elements of the entire lamp (claim 1), not comprised in claim 2. That it was not confined to the filament made as described in the body of the specification. Notes. This case appears to be the first in which the claim in a "pioneer invention" has been construed in as wide a sense as it will bear. The earlier failures did not point away from the use of carbon of very narrow cross-section in a vacuum, as it was well known that such a solution of the lighting problem was the true one, but they did not show a practical method of obtaining the light. The addition to public knowledge constituting the essence of the invention lay in showing the public how to get a carbon of the requisite thinness, and also in showing that by adopting the horse-shoe shape the danger of a breakdown (as in Swan's lamp) through expansion of the carbon could be avoided. 1887. EDISON & SWAN UNITED ELECTRIC LIGHT Co. v. WOODHOUSE & RAWSON (2nd Action), 4 R. P. C. 99. Construction of Claims-Sufficiency. A patent was granted (No. 4847 of 1878), to F. J. Cheesbrough for "improvements in and relating to electric lamps," [and to a method of charging such lamps with an artificial atmosphere and purifying the same], and to the production of a carbon for use in electric lamps, [and for other purposes.] 1 The object of the invention was described as twofold: an improved lamp, and the "production of a better carbon for the use of electric lamps." The drawings and lamp were described at length. The lamp consisted of a rod of carbon in an atmosphere of nitrogen. The defects in existing carbons were pointed out, the chief being want of homogeneity. The new process of preparing carbons was then described as follows:— "It has been found that a pencil of carbon immersed in a hydrocarbon gas or liquid, and heated to an extremely high temperature by the voltaic current, is not itself attacked, but decomposes the surrounding matter, the carbon of which enters and fills up its pores to an extent impossible except with matter in a very attenuated state, and deposits a perfectly homogeneous layer, generally of a bright grey colour, upon the exterior surface. As the carbon increases in size, more current is required to maintain its temperature, and if the current is gradually increased in accordance with the demand for it, there is appearingly no limit to the increase in mass of the homogeneous exterior deposit. Carbon pencils may be cut from this deposit, or the original pencil with its coating may be used in the lamps. "In this process it will be seen that the carbon is never in contact with the liquid in which it is immersed, but surrounded by a carbonic gas of very high temperature. Beeswax, balsam, and most oils, if pure, operate satisfactorily; almost any hydrocarbon, in fact, will answer." The mode of filling the globes with nitrogen gas had been described; the carbons were to be treated as above mentioned, thus: "let it be supposed that the pencil of carbon, held between two carbon pieces of greater mass than that of the pencil as above described, is immersed in the hydrocarbon liquid and heated in the manner already described, being then cleansed in alcohol, the pencil and its holders without having been disturbed are placed in the globe in which they are to be hermetically sealed. "The globe is charged with pure nitrogen, and then while still allowing pure nitrogen to flow into and out of the globe, the carbon is heated to incandescence, thus driving out all impurities and occluded gases, which are carried out of the lamp by the current of nitrogen. With this operation the preparation of the carbon is completed, and the lamp now being hermetically sealed as above described, is ready for use." The claims were— "First, the herein-described method of preparing the illuminating part of an electric lamp consisting of electrically heating the same, while it is surrounded by a carbon gas or liquid. "Second, a material for the manufacture of the illuminating conductors of electric lamps, produced by electrically heating carbon in a carbon gas. 1 The specification was amended from Nov. 12, 1884. The words in brackets were struck out (as to which see ante, p. 167) from the title, and the description of the corresponding parts from the specification. Only so much of the amended specification is here given as is necessary to appreciate the question of "construction." |