such as pure nitrogen "which does not react with heated carbon at the temperatures involved * * *”

The board sustained the rejection of claims 1-3, 5-8, 12-14, 16, 22, and 27 on Hitchock in view of Coxe, relying principally on Hitchcock. It reversed a similar rejection of claims 23 and 26. It also sustained the rejection of claims 9, 10, and 11, stated by the examiner to be on Hitchcock in view of Coxe further in view of two other patents and the British patent, the board relying only on the British patent.

Appellants emphasize that the Hitchock process is a flotation process wherein the glass sheets actually float on the molten metal of the bath. They urge that their method is fundamentally different and involves supporting the glass "in a state of equlibrium between the forces of surface tension and gravity." The board, they state, erred in assuming that Hitchcock's flotation bath is in a state of equilibrium between the forces of surface tension and gravity. They urge that the board also erred in assuming that mercury, proposed by Hitchcock for the bath in his auxiliary chamber 13 could be used, contending to the contrary that mercury vaporizes at 357°C. and "would have become a gas before the hot sheet actually touched it."

Turning to claim 1, quoted above, the appellants urge that Hitchcock does not show an organization in which a sheet is deposited on a solid floor and moved over it or in which there is interposed between the sheet and the floor a support of molten metal "of thickness measured above the floor not substantialy greater than that of the glass sheet" and "not larger than the glass sheet." They further contend that a flotation bath must be larger than the sheet it supports and that the molten metal support recited in the claim therefore cannot be a flotation bath. Concerning this claim, the board said:

***We read the bottoms of beds 5 and the bottom of the mercury bed in chamber 13 of the reference as being floors. In fact, Hitchcock describes the latter as "floor" in line 16 on page 2. We note also with respect to the floor of beds 5 of the reference, which are slightly curved, that the term "floor" as used in the claims before us need not be a flat horizontal surface or any other particular configuration unless the claims so specify. This is in accord with applicants' terminology, as exemplified in claim 22 which recites that "the floor is curved.”

Claim 1 recites that the support of "molten metal is of a thickness measured above the floor not substantially greater than that of the glass sheet, [not] larger than the glass sheet." Limiting the support of molten metal to the size of the sheet to be supported in Hitchcock is an obvious matter of choice. The relative thickness of the molten metal to the glass sheet, as broadly recited in this claim need not transcend the flotation principle of Hitchcock. Using just enough molten metal or mercury in this reference to just float the glass sheet,

which would be but an obvious expedient, would snbstantially meet the claimed relationship.

[1] The limitation in claim 1 that the support of molten metal is "not larger than the glass sheet" seems significant in distinguishing over Hitchcock where the glass sheet floats on the molten metal and, as shown in Fig. 1 of the patent (not reproduced herein), the lateral edges of the glass sheet are spaced inwardly a substantal distance from the lateral edges of the bath. The board's dismissal of the feature as "an obvious matter of choice" is not convincing in the absence of some reason why a person skilled in the art would find it obvious to depart from the flotation type of support of Hitchcock as well as from his dimensional disclosures. The rejection of claim 1, and claim 22 which is dependent thereon, will not be sustained.

Claim 2, supra, differs from claim 1, as may be seen, in referring to a "sheet of flat glass" without requiring that it be molten or otherwise specifying its temperature, and in not specifying that the molten metal support is not larger than the sheet. We think the board was correct in upholding the rejection of that claim. A "floor" need be no more than "The lower inside surface of any hollow structure"1 and we think that term is applicable to the bottom of Hitchcock's chamber 13. Mere selection of a "thickness measured above the floor not substantially greater than that of the glass sheet" would not by itself preclude the use of a bath deep enough to support the sheet by flotation or limit the method to one in which the molten metal provides the principal support for the sheet through surface tension. While appellants' argument that mercury vaporizes at a relatively low temperature indicates that the mercury in chamber 13 of Hitchcock would not be suitable for supporting glass in molten or plastic condition, the solicitor points out that in Hitchcock's process the glass sheet is cooled before it reaches the mercury bed. It cannot be concluded, on the present record and arguments, that the temperatures of the bath in Hitchcock's chamber 13 would be such as to make it inoperative for its disclosed purpose of completing the annealing of the glass sheet. Accordingly, the rejection of claim 2 will be sustained.

Claim 6 depends from and adds to claim 2 the limitation of "flowing a continuous sheet of molten metal beneath the glass sheet between the sheet and the floor," such flowing of the metal support being disclosed in connection with appellants' Fig. 3 as described above. The mercury bed in chamber 13 of Hitchcock, relied on with respect to claim 2, does not satisfy this limitation since it is clear that the mercury is placed in its chamber before the glass sheet is deposited and there is no "flowing" of it as a "continuous sheet" between the glass sheet and the floor during the movement of the glass sheet. Rather, the mercury acts as a substantially stationary flotation bed in which the

1 Webster's New International Dictionary, Second Edition, Unabridged, 1954.

as

ribs or ridges in the floor "prevent any such movement *** would tend to produce uniformity of temperature at the ends of the bed." It also seems apparent that Coxe would not lead one skilled in the art to act contrary to this express teaching by flowing the mercury along the bed. The rejection of claim 6 is reversed.

Claim 3 also depends from claim 2, adding the limitation that the molten metal support "is noncapillary and supports the glass by surface tension." The board stated that the mercury employed for the "floating liquid" in Hitchcock "will inherently form a convex meniscus with the edges of the compartment since the liquid must fill the latter*** 2 It also commented that the claim "does not exclude buoyant force in addition." However, the claim sets forth the feature of support by surface tension emphasized in appellants' specification and the board's comments are not supported by any evidence that surface tension is a substantial factor in the flotation type of supporting beds of Hitchcock. The rejection of claim 3, and claim 5, dependent there from, will not be sustained.

Claim 7 depends from and adds to claim 2 the provision that "the metal support comprises a plurality of molten metal bearings." The board regarded the two molten metal baths of Hitchcock as a plurality of metal "bearings" while appellants seem to consider the term "liquid bearings" limited by their disclosure to an arrangement offering "meniscus supports" for the glass sheet. The board's position cannot be sustained, for one reason, because the claim requires that the plurality of metal bearings, however that term is construed, which make up the support be interposed between "a" receiving floor and the sheet whereas the molten baths 5 and 13 of Hitchcock are each on a separate "floor." Moreover, the Patent Office does not suggest that it would be obvious to modify the reference structure to meet the requirements of the claim. The rejection of claim 7 is reversed.

Claim 8 is independent and includes steps of flowing a thin sheet of molten metal over a supporting solid surface and laying a sheet formed from molten glass on "the flowing molten metal." The board held that claim readable on Hitchcock "wherein the mercury bed in chamber 13 is 'a thin sheet of molten metal,' which has been flowed into the chamber." However, Hitchcock does not disclose that glass in a molten condition is received in chamber 13 and appellants' contention that mercury would vaporize upon contact with glass at high

2 Hackh's Chemical Dictionary (3d id.) contains these definitions:

capillarity-The attractive force between two unlike molecules as shown by the wetting of a solid surface by a liquid, or by meniscus formation.

meniscus The crescent-shaped surface of a liquid in a tube, either concave (when the liquid wets the material of the container, as water and glass), or convex (when liquid does not wet, as mercury and glass).

temperature stands unrebutted with respect to glass at a temperature high enough to be molten. Also, for reasons apparent from our discussion of claim 6, the recitation of laying the glass sheet on the flowing molten metal is not only unsatisfied by the reference but is also contrary to its teaching. We therefore cannot sustain the rejection of claim 8 on the basis of Hitchcock's chamber 13 with its mercury bath. As to chamber 4 of Hitchcock which receives the molten glass, the solicitor commented at oral argument that he would not call the molten bath therein a "thin sheet," and we agree. The board did not suggest any reason why it would be obvious to modify the bath in chamber 4 to support molten glass on a thin sheet. In addition, the bed in chamber 4, like the mercury in 13, is restrained from flowing movement. The rejection of claim 8 will not be sustained.

Claim 12, supra, requires casting a sheet from molten glass and laying the sheet on molten metal "in a state of equilibrium between the forces of surface tension and the forces of gravity to receive and support the glass sheet ***." Claim 13 is similarly limited. While the board states that the "mercury in the reference," which mercury is in Hitchcock's chamber 13, is in the defined state of equilibrium, it does not explain how it reaches that conclusion. Appellants urge that the board erred in assuming that such equilibrium exists in the Hitchcock flotation bath and further state:

Our invention deals with "casting" flat glass by forming a sheet from molten glass and depositing it upon molten metal in a state of equilibrium between the forces of surface tension and gravity.

Because the mercury bath would vaporize if a molten sheet of glass were cast thereon, it plainly could not be used as the supporting means of these claims. Further, the record does not satisfy us that the recited condition of equilibrium would be attained when glass is floated on a metal bath as disclosed in Hitchcock. The rejection of claims 12 and 13 will not be sustained.

Claim 14 includes the requirement that molten flat glass be cast onto the upper surface of

an elongated bed of molten metal, which does not wet the glass, in a shallow trough which is not wetted by the molten metal, to a depth which lifts the surface of the metal above the upper level of the trough *

In Hitchcock, only the molten metal in tank 4 is disclosed as suitable for receiving molten glass and there is no disclosure that the tank is not wetted by it. Neither is it disclosed that the metal there is in a shallow trough to a depth which lifts the surface of the metal above the upper level of the trough which, as appellants disclose, permits the glass sheet to pass over the edge of the trough without being bent