delivered the opinion of the court.
The main question in this case is: Do the city’s specifications tend to restrict free competition among *78bidders, in violation of section 74 of the Local Improvements Act (J. & A. 1466) 1 This main question is to be determined, as it seems to us, by the decision of either one of two questions of fact, viz.: (1) Do said specifications prescribe a creosote oil which cannot be made without infringing the Reilly ..patent, No. 1,220,001, issued March 20, 1917? (2) Do said specifications tend to foster a monopoly in the manufacture of creosote oil and creosoted wooden paving blocks ?
If said specifications'prescribe a creosote oil which cannot be made without infringing said Reilly patent, the validity of which patent is not questioned, we think that any contract based thereon is void.
In Siegel v. City of Chicago, 223 Ill. 428, it is decided that, under section 74 of the Local Improvements Act (J. & A. ft 1466), a municipal corporation cannot prescribe in the ordinance for a special assessment improvement the use of a patented article or material which can be obtained from only one person, firm or corporation, even though the latter agrees to furnish the same to any bidder on the contract at a fixed price. The vice in specifying a patented article in an ordinance is that it tends to restrict free competitive bidding. In Fishburn v. City of Chicago, 171 Ill. 338, it is decided that if the ordinance does not show, on its face, that .the article specified is patented or controlled by a single owner that fact may be proved. The above decisions were followed in the case of Village of Rossville v. Smith, 256 Ill. 302, 305. And we are unable to see any difference in principle between a case where the ordinance specifies a patented article, and a case where the specifications under the ordinance specify such an article. And we think that a court of equity has jurisdiction to restrain the performance of a contract which tends to restrict competitive, bidding or which is otherwise illegal or void. (Loeffler v. City of Chicago, 246 Ill. 43; Stevens v. St. Mary’s Training *79 School, 144 Ill. 336; Holden v. City of Alton, 179 Ill. 318; City of Chicago v. Hanreddy, 211 Ill. 24.)
In the Rossville case, supra, the ordinance specified a pavement to be paid for by special assessment. The ordinance did not in terms prescribe the use of a patented article, but evidence was introduced to show that the pavement described could not be constructed without infringing a certain patent. The trial court overruled the objections and entered judgment of confirmation, which judgment the Supreme Court reversed, and remanded the cause with directions to sustain the objections. In the reported opinion of the court the specifications for the wearing surface are set forth, as are also portions of the specifications of said patent, the validity of which patent was not questioned. The question to be decided was whether the materials, treated as required by the specifications of the ordinance, would produce the patented pavement. From said opinion it appears that the objectors called as a witness an experienced chemical engineer. He testified to the results of a laboratory test made by him, and that the proportion of the different grades of stone, sand, dust and asphalt specified in the ordinance was substantially the same as in said patent, and that the pavement produced would be an infringement of said patent. The court (p. 311) says:
‘ ‘ This testimony clearly shows an infringement, and it was not met by the testimony of appellees. No attempt was made to show any other laboratory test, or to show that the voids in a pavement constructed according to the specifications would not be less than 21 per cent or that the pavement would not have inherent stability. Three ’witnesses were examined on behalf of the appellee, and were of the opinion that the pavement could be constructed in accordance with the specifications without infringing the patent. * * * Evidence was given that the amount bid for the contract was reasonable, but such evidence was immaterial. *80The ordinance, because it prevented competition, was not within the power of the council to pass. ’ ’
The analogy between this Rossville case and the present case is somewhat striking. In the Rossville case it appeared that the pavement could not be constructed without infringing the two basic elements of the patent, viz., inherent stability and less than 21 per cent of voids. These elements were not in terms mentioned in the ordinance yet it appeared from the proof that the ordinance pavement would contain them. In the present case the specifications do not mention the products described in claims 1, 2 and 3 of the Reilly patent, which are the basic elements thereof, yet it appears from the testimony of complainants’ expert witnesses, Kirschbraun and Miner, that a pavement cannot be constructed according to the instant specifications without using a creosote oil which contains the products described in said three claims. Both of these witnesses were experienced chemical engineers, accustomed to construe patents and specifications. Kirschbraun had previously been employed for a period of about 3 years by the City of Chicago as a chemist in the asphalt testing laboratory and Miner had frequently testified in patent causes on chemical questions. By agreement between counsel for complainants and counsel for the City of Chicago, two samples of the Chicago oil, as described in the instant specifications, were delivered to Kirschbraun for the purpose of his making tests thereof, on condition that Mr. Eaton, chemist for the city, be present at such tests. Two tests were made,—the first by Kirschbraun in the presence of Eaton, and the second by Kirschbraun and Miner in the presence of Eaton. Both Kirschbraun and Miner testified that the samples of oil they tested conformed with the oil as described in the instant specifications and that the products mentioned in claims 1, 2 and 3 of the Reilly patent were *81present in the samples of oil tested by them. There was read to each of these witnesses the exact wording of said three claims and each testified that the description in each of said claims correctly described the ingredients of the samples of oil tested by them, and that the “waxy material” and the “hard material,” of the specific gravities mentioned, and the ‘ suitable solvent ’ ’ were present in said samples. Kirschbraun’s original notes of both tests were offered in evidence. And both Kirschbraun and Miner expressed the opinion, based on said tests, that said samples infringed the Reilly patent. The defendants did not offer any laboratory tests, or reports based thereon, in rebuttal of this testimony. The chemist for the city, Mr. Baton, who was present when Kirschbraun and Miner made their tests, was not called as a witness by the defendants to question in any manner the methods used or the results obtained by complainants ’ experts, and this, we think, is somewhat significant. On behalf of the defendants, Peter C. Reilly, the patentee and president of the Republic Co. (the paving blocks manufactured and treated by which company, the contractor, Ryan Company, stated in its bid it proposed to use), testified that in Ms opinion “the Chicago oil was not Ms patented oil.” The witness, Weiss, although it appears he made certain" tests for certain purposes of samples of oil received from various gas works, did not test any sample of the Chicago oil and did not express any definite opinion as to whether or not the same infringed the Reilly patent. And the witness, Murphy, never tested any sample of the Chicago oil with reference to the Reilly patent. It thus appears that Mr. Reilly, the patentee, was the only witness for the defendants who expressed an opinion on the question of infringement contrary to the testimony of complainants’ witnesses, Kirschbraun and Miner, and his opinion is unsupported by any laboratory tests of the Chicago oil, or by any *82reports based thereon. We do not think that his unsupported opinion should prevail over the testimony and opinions of said witnesses for complainants. In the Rossville case it seems that the court gave greater weight to the testimony and opinion of one witness, based upon facts disclosed from a laboratory test, than to the contrary unsupported opinions of three witnesses.
In some cases chemical or laboratory tests are necessary to determine questions of infringement of the claims of a patent. This clearly appears in Byerley v. Sun Co., 181 Fed. 138; 184 Fed. 455; Byerley v. Barber Asphalt Paving Co., 230 Fed. 995; Kuehmsted v. Farbenfabriken of Elberfeld Co., 179 Fed. 701, 705; General Bakelite Co. v. Nikolas, 225 Fed. 539, 555; General Electric Co. v. Laco-Philips Co., 233 Fed. 96, 97. We think that this is such a case. The above citations also disclose that infringement cannot be avoided because tests are necessary to determine infringement. And we think that any method of test may be employed which will fairly determine the question. In the present case it was shown by complainants’ expert witnesses, Kirschbraun and Miner, that the method they used - in testing the Chicago oil was a sufficient and proper method to determine the presence therein of the patented ingredients mentioned in claims 1, 2 and 3 of the Reilly patent, and that said ingredients were in said oil. On the trial counsel for defendants made no direct attack upon the tests made by them, but seemed to assume in cross-examination of said witnesses that the determination of the question of infringement depended upon whether the city’s specifications,' following only the tests mentioned therein, would produce the products described in said three claims of the Reilly patent, and counsel here base an argument on such assumption. We think the assumption is erroneous. The city’s specifications do not *83prescribe a method for producing oil but only a method for testmg oil already produced and proposed to be used in a contemplated pavement. The tests mentioned in the city’s specifications were not intended to determine questions of infringement. While the city’s specifications require that the oil submitted shall have certain properties, said specifications do not refer to the patented products, and, as it seems to us, an expert in making tests of the Chicago oil to ascertain whether it infringes said claims of the Beilly patent should not be confined to the tests mentioned in the city’s specifications. If the tests made by complainants’ experts had been confined only to the tests set out in the city’s specifications, but one thing would have been disclosed, viz., that the oil so tested conformed to the city’s specifications. We think that the tests for infringement must be carried far enough to show the chemical or physical constituents of the oil, and, if by such tests those constituents are found to be the products mentioned in said claims of the Beilly patent, then the patent is infringed. Furthermore, claims 1 and 2 of the Beilly patent mention no temperature limits. Claim 3 mentions a temperature “of at least 700 degrees F.” It is the law regarding patents that infringement depends upon a violation of the claims of a patent as distinguished from the specifications. The city’s specifications fix the heat limit, to be applied in testing oil to determine whether it meets said specifications, at 355 degrees Centigrade (671 degrees F.). And it appears from the testimony of complainants’ experts that the last-mentioned degree of heat will not disclose the Beilly patented products, yet that they are present in the Chicago oil, as can be shown by applying greater heat.
While defendants’ witness Beilly, the patentee, was on the stand and was being interrogated by the chancellor, he stated in effect that no prosecution for in*84fringement of his patent would be commenced against any one who saw fit under a contract with the city to furnish the creosoted oil called for by the city’s specifications. This statement estops Mr. Reilly. But the menace of the patent remains, and will remain during* the life thereof until successfully attacked in a court of competent jurisdiction.
Our conclusion is that the city’s specifications prescribe a creosote oil which infringes said Reilly patent, and that said specifications on that account tend to restrict. free competition among bidders in violation of section 74 of the Local Improvements Act (J. & A." 1466), and that the contract of the Ryan Company is void.
On the question whether said specifications tend to foster a monopoly in the manufacture of creosote oil and creosoted wooden paving blocks, we have also reached the conclusion, after a careful consideration of the record before us, that they do so tend.
For the reasons indicated the decree of the Circuit Court will be reversed, and the cause remanded with directions to that court to issue the injunction as prayed in complainants’ bill.
Reversed and remanded with directions.