(after stating the facts as above). Two thousand pages of record and six hundred of argument (approximately) cannot be reflected in detail within the limits of an opinion *393of reasonable length. After all, an opinion in a patent case is a special finding of facts and thereupon an application of the law. So we shall come at once to the finding of ultimate facts, to which we are led by an extended examination of the record and consideration of the arguments, without setting forth the conflicts of assertions and of theories in the evidence.
Prior to 1896 the calcining of cement materials in rotary furnaces had been fully developed. Prom Figure 1 of the patent, take away removable chamber 12 (which appellants, by an argument we accept for the purposes of this case, eliminate from the claims in suit) and place the burner B with the plate 15 at the entrance 10, and thereby the structures of the prior art are exactly brought to view, except that B would then appear as an injector of oil or gas, instead of powdered coal.
It was known that the calcining of cement materials required very high temperature. This was obtained by the rapid and complete combustion of the fuel. An atomizer injected a stream of mingled air and particles of oil. The plant had a large and tall stack. The rotary kiln (60 feet and up-wards in length) was itself a direct and unobstructed flue leading into the stack. Large volumes of heated air were brought in through the “conduit F” to effect the rapid and complete combustion of the fuel stream. The current of the kiln was naturally slowest at the circumference, growing more and more rapid toward the axis. Along the axis therefore the injected fuel stream was carried, drawitig upon the enveloping stream of air to complete the combustion, and forming a long candle-like flame that heated the walls of the _kiln and the cement materials by radiation rather than by direct impingement of the fuel while yet unconsumed.
Use of fine and dry coal for heating purposes was old. The smaller the particles, the greater their surface in relation to weight and the easier their sustainability in a current of air. Means had been employed for “converting the solid fuel into an impalpable powder to which the term ‘floating’ might be applied.”
Burners or injectors for using the impalpable coal powder for heating purposes bad been devised." Some of them are shown in the following cuts from the Westlake patent for “feeding fine fuel.”
*394Combinations of such coal injectors with boiler furnaces and smelting ' furnaces had .been made. McAuley’s combination, for example, was this:
Burning powdered coal in boiler furnaces and the like was not commercially successful. Not because the feeding and injecting apparatuses would not work; not because the powdered fuel would not thus burn and produce sufficient heat; but because in the obstructed passages and turns of such furnaces the fuel stream in combustion directly impinged upon fire arches or other parts and melted them down. . .. _ .
Appellants’ assignors were not the fathers of the conception of adapting a coal injector for use in the rotary cement kiln in place of the oil injector. Siemens had patented in England a combination of a rotary kiln for calcining ores and cement materials and an injector for burning gas and also an injector for burning powdered coal. The latter is thus illustrated:
Of this Siemens said:
“If pulverized or liquid fuel is employed in place of gas an arrangement of tlie nature shown in Figure la may be employed, where the fuel is introduced in a continuous stream or in small quantities into the receiver 1, whence it is blown by preference by a steam jet 2 so as to issue 'in a divided condition through the pipe 8 into the end of the rotating drum A, where it enters into combustion with the heated air passing in through the passages F, as before described.”
*395Crampton also had an apparatus of the same general principle:
He stated:
“I prefer to heat the chamber by injecting into it a mixture of air and finely powdered carbonaceous material, in the maimer described in the specifications of previous patents granted to me, and now well known and employed for heating revolving puddling furnaces.”
Neither the Siemens nor the Crampton patent, in its lifetime, made any impress upon the commercial manufacture of cement. That either of them was impracticable we do not find.
From 1896 on there has been an.immense and increasing consumption of cement. This has come rather from the great impetus to building and business in general during these times than from the disclosures of the Hurry and Siemens patent in 1900.
Prior to the issuance of the patent the applicants were burning powdered coal in rotary cement kilns at the Atlas plant by means of the high-pressure injector described in tlieir specification. About this time there was a very large (200 to 300 per cent.) increase in the price of petroleum, and a general uncertainty arose as to future supplies. In some localities where the supply seemed assured and the price satisfactory the use of oil injectors has continued. But most of the cement makers were confronted with the desirability, if not necessity, of getting a cheaper fuel. At this time many practical cement makers, including directors of appellee’s operations, were under a general belief, without any investigation of the matter, that powdered coal could not be used successfully in cement manufacture. Possibly a few makers, outside the Atlas plant, learned something of the particular apparatus by which the Atlas result was obtained, though the record does not clearly convict any one. But many, including appellee, must he acquitted of having any knowledge except that powdered coal was being used in the actual commercial manufacture of cement clinker at the Atlas works. They had then (before 1900) in their plants the complete present-day rotary kilns in operation with oil injectors. These men, skilled in the arts involved (the art of building cement plants and the art of burning cement clinker in rotary kilns with fuel-oil injectors), knew how much cement material was fed into the upper *396end of the kiln, how long it took the material to work down to the discharge end, how much oil in relation to finished product had to be carried in the form of fine particles by the air current into the suction of the kiln-and-stack draft, and how the flame, the walls of the kiln, and the cement materials appeared during the calcining process. Their problem was to substitute for the oil injector a coal injector that would give practically the same result in their existing rotary kilns. For this purpose they could- turn to the known prior-art coal injectors. While McAuley and Westlake showed forms of coal injectors and Siemens and Crampton asserted the applicability of such injectors to the rotary kiln, none answered certain particular questions on which would depend the success of the coal flame in producing substantially the result of the oil flame. In relation to kiln and stack what should be the dimensions of the blower and the air nozzle? What the capacity of the conveyor for feeding the impalpable coal powder to thé air blast ? What the size of the burner tube for delivering the stream of mingled air and particles of coal into the kiln? And beyond structural details what should be the speed of the blower in relation to that of the coal conveyor? How much coal per unit of time should be fed ? What proportion of the total air should come through the blower and what through conduit F, in order that the fuel stream should be projected a sufficient distance within the vortex of the kiln-and-stack suction ? There were the appliances, and the desired result was known. How attain it? Cut and try. And so these men, skilled in the art of calcining cement materials in their rotary kilns by the use of oil injectors, tested the interdependent matters of coal feed and air supply, as above suggested, and presently their experience as practical cement burners gave them control of the operative relations between their existing rotary kilns and the coal injectors of the McAuley and Westlake types. On the average about 90 days were required to achieve the final adjustment of the parts and the ultimate control of the flame. And not one instance of failure is recorded.
Our conclusion from the file-wrapper is that the Patent Office, though some of the most potent references were not before it, rejected all pretensions that the applicants were entitled to a monopoly of a generic combination of a rotary kiln and a coal injector. Applicants sought to avoid the combination of coal injectors (by fan or blower) with boiler furnaces by alleging that the flame, diffused by fire-arches and other obstructions, was not the flame they obtained in the rotary kiln. Therefrom the inference would seem to be that a fuel stream from a McAuley burner would be too diffuse to work when injected into the Unobstructed vortex of the kiln-and-stack draft. If this mistaken urge was influential in securing a patent, the applicants should not be allowed now to pick up their discard. But, despite the argument, ,the Office required the applicants to claim their specified means, and further to limit the combinations of their means by reciting the particular conditions that should result from the specified operation of their means.
Apart from the file-wrapper, we think the meaning of the patent as granted is sufficiently plain. To builders it said: “Make a coal in*397jector in substantial accordance with our drawings and description; attach it, as shown, to the existing rotary kiln; and you will have a complete operative device.” To experienced cement burners: “Have about 20 pounds pressure in your air-tank; open the valve in the air nozzle until about 2 per cent, of the total volume of air going up the kiln and stack is coming from the pressure tank. This will start a fuel stream through tube 33, arid at the same time create a vacuum equal to 5 or 6 pounds in fuel chamber 30. Outer air will be drawn in through ports .'¡o and later through ports 38 to envelop and hold relatively compact the fuel stream. The use of this limited volume of high-pressure air will cause the fuel to be injected in a long compact body so that a long, concentrated, intense flame will be produced. When the fuel stream reaches the kiln, it will be further enveloped by the air from conduit F so that the flame will not impinge upon the walls of the kiln and the cement materials. By regulating the valve in the air nozzle and the closable ports J¡5, you will readily learn to burn cement as well as you did with the oil injector.” So in the claims the means for creating “a jet of air of high pressure and small volume” refer unequivocally to the pressure tank or its equivalent for delivering air under substantially 20 pounds pressure and to the needle-valved nozzle or its equivalent for discharging substantially 2 per cent, of the total volume. And equivalency cannot be predicated simply upon the general result of calcining cement in a rotary kiln by the use of powdered coal.
Appellee does not use the “jet of air of high pressure and small volume” for injecting the coal into the burner tube. Its blower produces a pressure of three or four ounces. It does not have the additional air to envelop and hold compact the fuel stream on its way into the kiln. All the air that carries the floating particles of coal into the kiln comes from the blower except that small portion which unavoidably gets in with the fuel; and this, of course, is not the “additional air” of the patent. Unenveloped the stream of mingled coal particles and air goes into the kiln. Appellee's air-jet provides from 20 to 30 per cent, of the total volume. This is hardly the “limited volume” of the patent’s air-jet. Appellee does not have “a core of pulverized fuel” “to heat the walls of the furnace by radiation without impinging thereupon.” Its flame rolls and darts on its way up the kiln and to the extent that impingement is restrained the result is the inevitable action of the kilu-and-stack draft. A similarity is urged in this: That physicists may now measure the pressure of the fuel stream as it emerges from the exit of the burner tube in appellants’ and in ap-pellee’s structures and will find it substantially the same in each, about 1 y.± or 2 ounces. And, since this is relatively a high pressure compared with that of the draft in a boiler plant, the high pressure of the fuel stream as it enters the kiln is what the patent meant by the term “high pressure.” It remained for the experts to disclose the ranges >of speed at which the fuel may be injected into the kiln while an efficient flame is calcining the cement. In the patent no disclosure was made of the amount of air that came through the fixed ports 38 or should be permitted to come through the adjustable ports 1)5 — no specification of the volume and speed of the fuel stream at the exit *398of the' burner tube in relation to the volume and speed of the kiln- and-stack draft. None was needed. A competent cement burner, with the assurance that the tool would work, would adjust it until he had an efficient flame. But as to how to get a volume and speed of the fuel stream at the exit of the burner tube that would give an efficient flame the patent was definite and specific — impel your powdered coal by a 2 per. .cent, volume of 20-pound pressure air. If the ground of the patent should be permitted to be shifted to the volume and speed of the str.eam of mingled air and powdered coal as it enters, the kiln necessary to produce an efficient flame, appellants would be given a monopoly of the calcining of cement materials in rotary kilns by the use of powdered coal.
On the facts as we find them our conclusion of law is that claims 1 to 7, inclusive, are limited by their own terms and by the prior art to high pressure and small volume means; and that claims 8 and 9, unless likewise limited, are void as seeking to monopolize the general result. And consequently there is no infringement.
Appellee’s experimental use of high pressure and small volume means, long abandoned, would not warrant an injunction.
Hurry and Seaman were the first to burn powdered coal with commercially successful results in rotary kilns. So were the patentees in Westinghouse v. Boyden, 170 U. S. 537, 18 Sup. Ct. 707, 42 L. Ed. 1136, Kokomo Co. v. Kitselman, 189 U. S. 8, 23 Sup. Ct. 521, 47 L. Ed. 689, Cimiotti v. Fur Co., 198 U. S. 408, 25 Sup. Ct. 697, 49 L. Ed. 1100, and many other cases, the first to achieve their disclosed results. But that fact is not sufficient to shut off the public from using the common knowledge and the common skill in adapting other devices to produce the same result by a different principle of operation, especially where every underlying concept is old and has been fully disclosed.
The decree is affirmed.
Note. — Judge GROSSCUP participated in the hearing, consultations, and decision; but the opinion was not formulated until after his retirement.