Exothermic Compounds are compounds which evolve heat during their formation; these are usually stable compounds, as they must be supplied with a corresponding amount of heat for their decomposition.
Exot´ic, belonging to foreign countries; a term used especially of plants. Exotic plants are such as belong to a soil and climate entirely different from the place where they are raised. They are nearly always greenhouse or hothouse plants.
Expansion, in physics, the increase of the dimensions of a body caused by a change of temperature. In general, bodies expand with rise of temperature, solids expanding least and gases most. This change in the dimensions of solids with temperature is expansion in length, area, and volume. These changes are referred to a unit called the coefficient of expansion, or expansion of unit length, area, or volume for 1° rise. For example, the coefficient of linear expansion of iron is .000011; that is, a yard, say, of iron rod becomes longer by this fraction of a yard for each degree centigrade that its temperature is raised. The coefficient of volume expansion of a solid is three times its linear coefficient. Crystals have different rates of expansion along the three crystalline axes. Fused silica or quartz expands so slightly that it may be plunged when red-hot into water without being cracked. Invar, a nickel-steel alloy, which also has an extremely small coefficient of expansion, is used in making clock pendulums, which are unaffected by change of temperature. The observed expansion of liquids is affected by the expansion of the vessel containing them, and the apparent expansion of a liquid is thus always less than its real expansion. The expansion of water with rise of temperature is irregular; water contracts from 0° to 4°C., and thereafter expands at an increasing rate until the boiling-point is reached. The expansion of mercury and other liquids is employed in thermometry. Gases when kept at constant pressure expand by about 1/273rd part of their volume at 0°C. for each degree rise.
Expectation, in the doctrine of chances, the value of any prospect of prize or property depending upon the happening of some uncertain event. A sum of money in expectation upon a certain event has a determinate value before that event happens. If the chances of receiving or not receiving a hundred pounds, when an event arrives, are equal, then, before the arrival of the event the expectation is worth half the money.—Expectation of life, the number of years which a man or woman of any age may be expected to live. To calculate this with any reasonable degree of probability, it is necessary to have particulars of a large number of individuals. The earliest observations were based upon the records of the registers of certain towns. Out of a number of people alive at one date the numbers still living at the end of successive years were found, and an estimate of the probable duration of life was made. With increased facilities for collecting statistics of a larger number of lives, this estimate has since been modified. It is necessarily influenced by the progress of civilization, improved methods of sanitation, increased knowledge of the best methods of treating diseases, and other causes, but the collected statistics are now so numerous that the actuaries of life assurance offices have been able to prepare tables of mortality from which the cost of life premiums and the price of annuities are calculated.
Expec´torants are drugs used to increase and liquefy the secretion in the lungs and air-passages. The most effective are ipecacuanha, squills, apomorphine, ammonium carbonate, and
potassium iodide. Some of these are usually present in the many cough mixtures so widely used.
Exper´iment, an operation designed to discover some unknown truth, principle, or effect, or to establish it when discovered. It differs from observation in the fact that the phenomena observed are, to a greater or less extent, controlled by human agency. Experiment distinguishes the modern method of investigating nature, and to it we owe the rapid strides made in chemistry and physics.
Expert´ (Lat. experiri, to test), a person eminently skilled in any particular branch or profession; specifically, a scientific or professional witness who gives evidence on matters connected with his profession, as an analytical chemist or a person skilled in handwriting.
Exploits´, River of, a river which traverses nearly the whole of Newfoundland from S.W. to N.E., and falls into the Bay of Exploits. It is about 150 miles long, and is navigable for steamers for 12 miles.
Explo´sion, a sudden violent outburst accompanied by a loud noise, and giving rise to an impulsive wave which spreads outwards from the place of explosion. Generally applied to the very rapid combustion of explosive substances which, under the influence of heat or shock, are resolved with extreme rapidity into gaseous form. Substances are termed low explosives or high explosives according as they are set off by combustion or detonation.