The success of Joe and others of his kind depends also in this on a well known natural law.  It is that there can be no combustion in the ordinary sense where there is no oxygen.  As a candle will surely go out if enclosed in an air-tight receptacle—­that is, it will go out as soon as it has burned up all the oxygen—­just so surely will flame of any kind go out when a person closes his mouth on it.  And as there is scarcely any air in the closed mouth—­all of it going down the bronchial tubes into the lungs—­it follows that the flame dies out almost instantly.  That fact being considered, and the mouth and throat having been previously treated with the secret chemical, there is really not so much danger as appears.

As a matter of fact, a person inadvertently swallowing hot tea or coffee will burn or scald his mouth or tongue much more painfully than will a professional fire-eater.  Most people know how painful a burned tongue is.

Joe told something of the history of fire-eating “champions” to his audience of friends, for it appeared that he had been reading up on the subject and was well informed.  Then he announced that the private rehearsal was over.

“But I’m going to work this fire-eating up into something that will cause a sensation,” he said.  And he made good his promise.

It was about a week after this, and the circus had been traveling about, playing to good business, when Joe received a letter.  In the upper left-hand corner was the imprint of Herbert Waldon, Chemist.

“I hope he has some news about the circus tickets!” exclaimed Joe.  For the show had been losing money steadily by means of the bogus coupons; not as much as at first, but enough to make it necessary to discover the fraud.  And, so far, Mr. Moyne had not been successful.

“Perhaps this explains the mystery,” mused Joe as he opened the letter.

CHAPTER X

THE PET CAT

The typewritten sheet of the letter from Mr. Waldon enclosed two of the engraved circus coupons.  They fluttered to the floor of Joe’s private tent as he tore open the envelope.

“Well, either he has discovered something, or he has sent them back and given up,” mused the young magician.  “Let’s see what he says.”

Joe quickly took in the contents of the letter.  In effect it stated that Mr. Waldon had discovered which were the bogus and which were the real circus tickets.  He first gave an explanation of the chemical tests he used.  Joe read this hastily, but carefully, then passed to the conclusions arrived at by the expert, who was an authority on various kinds of paper, as well as chemicals.

“The ticket I have marked No. 1 is a genuine coupon, issued by your circus corporation,” said Mr. Waldon in his letter.  “The slip marked by me as No. 2 is a counterfeit.  You will observe that they both bear the red ink serial number 356,891.