The _cuvée_ completed, the blended wine, which in its present condition gives to the uninitiated palate no promise of the exquisite delicacy and aroma it is destined to develop, is drawn off again into casks for further treatment. This comprises fining with some gelatinous substance, usually isinglass, made into a jelly and strained through a 'tammy;' while, as a precaution against ropiness and other maladies, liquid tannin, derived from nut-galls, catechu, or grape husks and pips, is at the same time frequently added to supply the place of the natural tannin, which has departed from the wine with its reddish hue at the epoch of its first fermentation. If at the expiration of a month the wine has not become perfectly clear and limpid, it is racked off the lees, and the operation of fining is repeated. [Illustration] The operation of bottling the wine next ensues, when the scriptural advice not to put new wine into old bottles is rigorously followed. For the tremendous pressure of the gas engendered during the subsequent fermentation of the wine is such that the bottle becomes weakened, and can never be safely trusted again.[410] It is because of this pressure that the Champagne bottle is one of the strongest made, as indicated by its weight, which is almost a couple of pounds. To insure this unusual strength, it is necessary that the sides should be of equal thickness and the bottom of a uniform solidity throughout, in order that no particular expansion may ensue from sudden changes of temperature. The neck must, moreover, be perfectly round and widen gradually towards the shoulder. In addition--and this is of the utmost consequence--the inside ought to be perfectly smooth, as a rough interior causes the gas to make efforts to escape, and thus renders an explosion imminent. The composition of the glass, too, is not without its importance, as on one occasion a manufactory established for the production of glass by a new process turned out Champagne bottles charged with alkaline sulphurets, and the consequence was that an entire _cuvée_ was ruined by their use, through the reciprocal action of the wine and these sulphurets. The acids of the former disengaged hydrosulphuric acid, and instead of Champagne the result was a new species of mineral water. Most of the bottles used for Champagne come from the factories of Loivre (which supplies the largest quantity), Folembray, Vauxrot, and Quiquengrogne, and they cost on the average from 28 to 33 francs the hundred.[411] They are generally tested by a practised hand, who, by knocking them sharply together, professes to be able to tell, from the sound that they give, the substance of the glass and its temper, though occasionally a special machine, subjecting them to hydraulic pressure, is had recourse to. [Illustration]