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(30.) It frequently happens that the stopper of a glass bottle or decanter becomes fixed in its place so firmly, that the exertion of force sufficient to withdraw it would endanger the vessel. In this case, if a cloth wetted with hot-water be applied to the neck of the bottle, the glass will expand, and the neck will be enlarged, so as to allow the stopper to be easily withdrawn.

(31.) The contraction of metal consequent upon change of temperature was applied some time ago in Paris to restore the walls of a tottering building to their proper position. In the Conservatoire des Arts et Métiers, the walls of a part of the building were forced out of the perpendicular by the weight of the roof, so that each wall was leaning outwards. M. Molard conceived the notion of applying the irresistible force with which metals contract in cooling, to draw the walls together. Bars of iron were placed in parallel directions across the building, and at right-angles to the direction of the walls. Being passed through the walls, nuts were screwed on their ends, outside the building. Every alternate bar was then heated by lamps, and the nuts screwed close to the walls. The bars were then cooled, and the lengths being diminished by contraction, the nuts on their extremities were drawn together, and with them the walls were drawn through an equal space. The same process was repeated with the intermediate bars, and so on alternately until the walls were brought into a perpendicular position.