ON PETITION FOR REHEARING
Carter-Wallace has petitioned this court for reconsideration of our decision of November 14, 1972, p. 529, holding its patent on the drug meprobamate to be invalid. It argued that our ruling that the patent application failed to disclose meprobamate’s tranquilizing properties, and therefore that those properties could not be considered in assessing the validity of the patent, at 540-543, was a finding of fact on an issue which the district court, because of its differing view of the applicable law, had not considered and on which no expert testimony had been presented. It asked that the case be remanded to the district court to take further evidence and make findings on what it contends to be this newly determinative issue. We called upon appellee to answer. After careful consideration, we find no infirmity in our decision.
The adequacy of a patent application’s disclosure is a mixed question of law and fact, on which the court must ultimately apply a legal standard to a complex set of facts. There can be no doubt that expert testimony will often aid in understanding the underlying factual context. But the resolution of the legal issue is for the court, Minnesota Mining & Mfg. Co. v. Carborundum Co., 155 F.2d 746, 749 (3 Cir. 1946); Watson v. Bersworth, 102 U.S.App.D.C. 187, 251 F.2d 898, 900, cert. denied, 356 U.S. 972, 78 S.Ct. 1135, 2 L.Ed.2d 1146 (1958), and when it is clear that the disclosure of the patent application does not meet the statutory standard, expert assistance is not necessary either in the district court or on review,. Cf. Kohn v. Eimer, 265 F. 900, 902 (2 Cir. 1920).
That is the case here. This issue was fully briefed by both parties and we had the benefit of Judge Dooling’s exhaustive findings of fact, 341 F.Supp. 1303, based in large part on expert testimony concerning the relevant chemical concepts, in reaching our decision. We saw then, and we see now, no need for a remand. There is simply no room for plausible argument that the tranquilizing property of - meprobamate was disclosed in the patent application in accordance with the *548standard set out in section 112. Carter-Wallace relied only on the anticonvul-sant and muscle-paralyzant properties of meprobamate to establish patentability before the Patent Office, did not urge the tranquilizing property as an additional basis of patentability, and did not establish this property as it would have been obliged to do if it had relied upon it. It is apparent that neither of the Patent Examiners — who possessed considerable expertise in this field and were under a statutory obligation to conduct an independent examination of the merits of the application — understood the application to disclose the drug’s tranquilizing effect. At no point in the Patent Office proceedings was the tranquilizing property mentioned. At no point did the Patent Office have the opportunity to evaluate what is now claimed to be this basis of patentability against the relevant prior art.
Moreover, correspondence cited by Davis-Edwards lends support to its argument that Dr. Berger himself regarded the CIP application as disclosing only anticonvulsant and muscle-paralyzant properties. His letter to Carter-Wallace’s patent counsel, on which the CIP application was largely based, made no mention of the drug’s use in the treatment of anxiety. In light of this correspondence, and the fact that meproba-mate’s effect on the interneurons is as relevant to its muscle-relaxant or muscle-paralyzant property as it is to the tranquilizing property, we are convinced that the few sentences on which Car ter-Wallace bases its argument of disclosure were intended as, and were understood as, part of the patent’s discussion of meprobamate’s muscle-relaxant property.
Indeed, the petition for rehearing does not claim that there is anything in the patent application which clearly teaches meprobamate’s tranquilizing properties. Instead, Carter-Wallace suggests that some skilled workers in the art might have been led to experiment with meprobamate as a tranquilizer on the basis of the application’s reference to “anxiety” and its disclosure of meprobamate’s longer duration of action. But this is not sufficient. We reiterate that a high standard of disclosure is required before a novel property of an otherwise obvious chemical compound can be relied upon to establish patentability. A disclosure is not adequate if it is merely a suggestion of the art which might lead others to hit upon the property relied upon for patentability. The disclosure of a patent should, upon issuance, immediately add a patentable invention to the existing fund of knowledge in the field; it must do more than merely suggest experimentation which would lead to the discovery of the patentable property.
This is not new law; this court has said much the same thing many times before. Thus, in Harries v. Air King Products Co., 183 F.2d 158 (2 Cir. 1950), we held that the patented invention was limited to the disclosure of radio vacuum tubes which utilized an electron stream of comparatively great length, and that the patent did not cover tubes in which the ratio of the length of the electron stream to its cross-section was large, notwithstanding the patentee's argument that this latter property was implicitly disclosed in the text and diagrams of the patent application. Judge Learned Hand’s words are in point here-:.v
Even though it were possible that a person skilled in the art might see that it was not absolute length, but the ratio of length to cross-section that was important, we should not be justified in validating such an expansion of the original; it is the sort of artful extrapolation against which courts have over and over set their faces. ... A patent must be a certain guide; not a congeries of pregnant suggestions.
Similarly, the Court of Customs and Patent Appeals has long followed the rule of Brand v. Thomas, 96 F.2d 301, 303, 25 CCPA 1053 (1938):
Lack of clear disclosure is not supplied by a- speculation as to what one skilled in the art might do or might not do if *549he followed the teaching of the inventor. The disclosure should be clearer than to suggest that one skilled in the art might construct the device in a particular manner.
We see nothing in the decisions of the District Court of the Southern District of New York or of this court in a previous litigation involving the meproba-mate patent, Carter-Wallace, Inc. v. Riv-erton Laboratories, Inc., 304 F.Supp. 357 (S.D.N.Y.1969), aff’d, 433 F.2d 1034 (2 Cir. 1970), which is inconsistent with our conclusion. While Carter-Wallace relies on statements of both courts seeming to accept that the tranquilizing properties of meprobamate had been disclosed, see 304 F.Supp. at 361; 433 F. 2d at 1040, in neither court was there dispute that these properties had been disclosed. It is thus neither surprising nor significant that these courts mentioned in passing Carter-Wallace’s characterization of the disclosure of the patent application; it is more' significant that this court, in its description of the continuation in part application, 433 F. 2d at 1036, noted only the disclosure of anticonvulsant and muscle-paralyzant properties. Carter-Wallace also points to a statement by the district judge in Riverton which it claims “excused” the failure of the patent application to specify meprobamate’s tranquilizing properties on the ground that human testing had not been completed and therefore “[n]o positive representation of such use could have been made at that time.” 304 F.Supp. at 365. But this statement was made in the context of Riverton’s claim that the failure to disclose that the drug was intended for human use was a fraud on the patent office which made the patent invalid. Judge Can-nella merely held that the failure to disclose “such [intended human] use” was not fraudulent; no question of the adequacy of the disclosure for purposes of patentability was presented, nor was the question of disclosure of tranquilizing properties in particular at issue. At most, Judge Cannella’s remark might be construed as indicating his belief that no “positive representation” of human use could have been expected at that time. But this would not excuse the failure to disclose meprobamate’s tranquilizing property; in any event, a reasonable excuse for failing to make a disclosure is not the equivalent of making one.
The petition for rehearing is denied.