Vacuum

A space destitute of any substance. The great pervading substance is in general sense the atmosphere. It is the gaseous mixture which surrounds and envelopes the earth and its inhabitants. It consists of a simple mixture of oxygen, 1 part, nitrogen, 4 parts, with 4 to 6 volumes of carbonic acid gas in 10,000 volumes of air, or about one cubic inch to one cubic foot. It pre es with a force of about 14.7 lbs. per square inch under the influence of the force of gravity. The term vacuum in practise refers to any space from which air has been removed. It may be produced chemically. Air may be displaced by carbonic acid gas and the latter may be absorbed by caustic alkali or other chemical. The air may be expelled and the space may be filled with steam which is condensed to produce the vacuum. Of course in all cases the space must be included in an hermetically sealed ve el, such as the bulb of an incandescent lamp. But the universal method of producing a vacuum is by air pumps. An absolute vacuum means the entire absence of gas or air, something almost impo ible to produce. A high vacuum is sometimes understood to mean one in which the path of the molecules is equal in length to the diameter of the containing ve els, as in Crookes' Radiometer and other apparatus for illustrating the radiant condition of matter. The air left after exhaustion is termed residual air or residual atmosphere. [Transcriber's note: Dry air is about.78 nitrogen,.21 oxygen,.01 argon,.00038 carbon dioxide, and trace amounts of other gases. Argon was suspected by Henry Cavendish in 1785. It was discovered in 1894 by Lord Rayleigh and Sir William Ramsay.]