Various precautions must be taken in the use of corks.  The bottles that lose their wine in consequence of the bad quality of their corks are many in number, and it is not long since that they were the cause of genuine disaster to the champagne trade.

Mr. Salleron has largely contributed to the improving of the quality of corks found in the market.  The physical and chemical composition of cork bark is peculiarly favorable to the special use to which it is applied; but the champagne wine industry requires of it an exaggerated degree of resistance, inalterability, and elasticity.  A 11/4 inch cork must, under the action of a powerful machine, enter a 3/4 inch neck, support the dissolving action of a liquid containing 12 per cent. of alcohol compressed to at least five atmospheres, and, in a few years, shoot out of the bottle and assume its pristine form and color.  Out of a hundred corks of good quality, not more than ten support such a test.

In order to explain wherein resides the quality of cork, it is necessary to refer to a chemical analysis of it.  In cork bark there is 70 per cent. of suberine, which is soluble in alcohol and ether, and is plastic, ductile, and malleable under the action of humid heat.  Mixed with suberine, cerine and resin give cork its insolubility and inalterability.  These substances are soluble in alcohol and ether, but insoluble in water.

According to the origin of cork, the wax and resin exist in it in very variable proportion.  The more resinous kinds resist the dissolving action of wine better than those that are but slightly resinous.  The latter soon become corroded and spoiled by wine.  An attempt has often been made, but without success, to improve poor corks by impregnating them with the resinous principle that they lack.

Various other processes have been tried without success, and so it finally became necessary simply to separate the good from the bad corks by a practical and rapid operation.  A simple examination does not suffice.  Mr. Bouche has found that corks immersed in water finally became covered with brown spots, and, by analogy, in order to test corks, he immersed them in water for a fortnight or a month.  All those that came out spotted were rejected.  Under the prolonged action of moisture, the suberine becomes soft, and, if it is not resinous enough, the cells of the external layer of the cork burst, the water enters, and the cork becomes spotted.

It was left to Mr. Salleron to render the method of testing practical.  He compresses the cork in a very strong reservoir filled with water under a pressure of from four to five atmospheres.  By this means, the but slightly resinous cork is quickly dissolved, so that, after a few hours’ immersion, the bad corks come out spotted and channeled as if they had been in the neck of a bottle for six months.  On the contrary, good corks resist the operation, and come out of the reservoir as white and firm as they were when they were put into it.