EXPANSION, (from the Latin, expando) that degree of increment, which a body is susceptible of extending in one or more of its dimensions by heat. Bodies of every kind, as far as WO are acquainted with them, are expanded in bulk by heat, and are contracted by cold ; and to this law there are but few exceptions, which will be noticed in due time. The expansions, or the increments of bulk, are not exactly proportional to the increments of heat in the same body ; nor are dill'erent bodies expanded alike by the like elevation of temperature. Thus, it' a quantity of water be increased one inch in bulk by the COMMOrlication of ten degrees of heat, the communication of twice or thrice as much nacre heat will not cause it to expand two or three inches more. Also, if a rod of gold, and another similar roil of glass, be heated to the same degree, their increments of bulk, :wising thereby, will not be equal, the gold expanding more than the glass.
Of the three principal states or natural bodies, viz., solids, liquids, and elastic fluids, the solids are expanded least ; the liquids are expanded more than the solids • lint the elastic fluids are expanded a vast deal more than the knowledge of the precise quantities of these expansions of' bodies is of great use in philosophy, in mechanics, and in other scientific subjects; hence no pains have been spared by philosophers to investigate and ascertain them ; various instruments have been contrived for that purpose ; innumer able experiments have been instituted ; and a great many useful results have been obtained. Of these results we shall now endeavour to give a regular and distinct amount.
The instruments which have been contrived for the par pose of measuring the expansions of solids arising. an elevation of temperature, are called pgrometerg. The objects which must be had in view in the construction of pyrometers, are to form a steady flame, wherein solids of a certain length may lie applied either successively, or several of them at the same time; some contrivance by which those metallic bodies may be heated to any required degree; and a mechanism capable of measuring the increase of bulk which is caused by the heat; and this may be accomplished by of multiplying wheels, by levers, by screws, by a microscopical micrometer, or otherwise.
Some of the first detertninations of the expansion of bodies, that may be considered its being sufficiently accurate, were made by Mr. Ellicot, with a pyrometer of his contrivance. Mr. Ellicot determined the proportional expansions of seven metallic bodies by the same elevation of temperature. They are as follow : Gold. Silver. 13rags. Copper. Iron. Steel. Lead.
73. 103. 95. 111. 60. 50. 149.
Snleaton contrived a much better pyrometer, and with it he determined the expansions of several solids.
De Luc also contrived a pyrometer of a peculiar con struction; but Air. 1Zamsden's pyrometer is superior to any other contrivance or the kind.
The folloWing table shows. in parts of an inch, how much one foot's length ()fall:rent substances is expanded by 180° of heat, Fahrenheit's scale, between the freezing :11“1 the boiling points of water. To the first seven substances (which were examined in Mr. Bamsden's most accurate pyrometer) there are added the expansions a single degree of heat. The others were determined by Mr. Smeaton with his rometer.
1''v n, 150° Standard brass scale, supposed to be Hamburg brass 0.0001237 . 0.0222016 English plate brass in 0 of a rod 0.00012u2. 0.0227130 English plate brass in form of a trough 0.0001263 . 0.0227380 Valirculici•,; Scale.
By 1° fly 180° Steel rid 0 0000703 . 0.013730S Cast-iron prism 0 0000740 . 0.01331211 Glass tube 0 . 0000517 . 0.00113138 Solid glass rod 0 0000539 . 0.00911941 White glass barometer tube 0.0100 Martial regnlus of antimony 0.0 I 30 Blistered steel 0.0138 llard steel 0,0147 Iron 0.0151 Ilismut h 0.0107 Copper hammered 0.0201 Copper eight parts, with tin one part . . 0.0218 Cast 0.0223 Brass sixteen parts, with tin one part . . 0.0229 Brass wire 0.033.2 Speculum metal 0.0232 Spelter solder, viz., of brass two parts, and of zinc one 0.0247 Fine pewter 0.0274 Grain tin 0.029k Soft solder, viz., lead two parts, tin one . . 0.0301 Zinc eight parts, with tin one, a little ham mered 0,0323 Lead 0.0314 Zinc or spelter 0.0353 Zinc hammered half an inch per lbot . . 0.0373 iron, instead of being condensed into a smaller bulk, expands in its transition from a fluid into a solid state; so that a quantity of iron occupies nacre room in the solid form than it does in a fused state.