EXPAN′SION

All substances, solid, liquid, and gaseous, when chemical change does not take place, expand by heat, and contract by cold. In some of them this property occurs in a greater degree than in others, but is constant for the same substance under the same circumstances. The chemist avails himself of this property in the construction of his thermometer; the wheelwright, in fixing on the tire of his wheels; the engineer, in restoring to the perpendicular the leaning walls of buildings, . This expansion by heat is of great importance in the manufactures, as allowance has to be made of it in every purpose where metals are employed. The following is a list of the expansion of the chief metals, ., when heated from 32° to 212° Fahr., or from 0° to 100° Cent.:— | Substance. | Expansion. | | In bulk. | In length. | | Gla | 1 in 384 | 1 in 1150 | | Platinum | 1 in 377 | 1 in 1311 | | Steel | 1 in 309 | 1 in 926 | | Iron | 1 in 282 | 1 in 846 | | Gold | 1 in 227 | 1 in 682 | | Copper | 1 in 194 | 1 in 582 | | Bra | 1 in 179 | 1 in 536 | | Silver | 1 in 175 | 1 in 524 | | Tin | 1 in 172 | 1 in 516 | | Lead | 1 in 117 | 1 in 351 | | Zinc | 1 in 113 | 1 in 340 | Of the liquids, they expand as follows, when heated from 0° to 100° Cent., or from 32° to 212° Fahr.:— | Mercury | 1 in 55 in bulk. | | Water | 1 in 21 in bulk. | Gases practically all expand alike; that is to say, for every degree Fahrenheit a gas expands 1 ⁄ 491 of its bulk at 32°, and for every degree Centigrade 1 ⁄ 273 of their volume at 0°C. An example will show the importance of this. Suppose an iron bar, connecting two sides of a building, and of a length of about 85 feet. The increase in length by heat of this bar would make it 1 inch longer in summer than in winter; and it would, if no allowance be made, pull or thrust the walls to this extent each year.