imported>Anthony.Sebastian |
imported>John Stephenson |
| (146 intermediate revisions by 5 users not shown) |
| Line 1: |
Line 1: |
| == '''[[Volatility (chemistry)]]''' ==
| | {{:{{FeaturedArticleTitle}}}} |
| ''by [[User:Milton Beychok|Milton Beychok]] (and [[User:Anthony.Sebastian|Anthony.Sebastian]])
| | <small> |
| | | ==Footnotes== |
| ----
| |
| {{Image|Vapor Pressure Chart2.png|right|250px|Example vapor pressure graphs of various liquids.}} | |
| | |
| In [[chemistry]] and [[physics]], '''volatility''' is a term used to characterize the tendency of a substance to vaporize.<ref>'''Note:''' To vaporize means to become a [[vapor]], the gaseous state of the substance.</ref> It is directly related to a substance' s [[vapor pressure]]. At a given [[temperature]], a substance with a higher vapor pressure will vaporize more readily than a substance with a lower vapor pressure.<ref>[http://www.bae.uky.edu/~snokes/BAE549thermo/gasesvapor.htm Gases and Vapor] ([[University of Kentucky]] website)</ref><ref>{{cite book|author=James G. Speight|title=The Chemistry and Technology of Petroleum|edition=4th Edition|publisher=CRC Press|date=2006|isbn=0-8493-9067-2}}</ref><ref name=Kister>{{cite book|author=Kister, Henry Z.|title=[[Distillation Design]]|edition=1st Edition|publisher=McGraw-Hill|year=1992|isbn=0-07-034909-6}}</ref> In other words, at a given temperature, the more volatile the substance the higher will be the pressure of the vapor in dynamic equilibrium with its vaporizing substance—i.e., when the rates at which molecules escape from and return into the vaporizing substance are equal.
| |
| | |
| In common usage, the term applies primarily to [[liquid]]s. However, it may also be used to characterize the process of [[Sublimation (chemistry)|sublimation]] by which certain [[solid]] substances such as [[ammonium chloride]] (NH<sub>4</sub>Cl) and [[dry ice]], which is solid [[carbon dioxide]] (CO<sub>2</sub>), change directly from their solid form to a vapor without becoming a liquid.
| |
| | |
| Any substance with a significant vapor pressure at temperatures of about 20 to 25 °[[Celsius (unit)|C]] (68 to 77 °[[Fahrenheit (unit)|F]]) is very often referred to as being ''volatile''.
| |
| | |
| === Vapor pressure, temperature and boiling point ===
| |
| | |
| The vapor pressure of a substance is the pressure at which its gaseous (vapor) phase is in equilibrium with its liquid or solid phase. It is a measure of the tendency of [[molecule]]s and [[atom]]s to escape from a liquid or solid.
| |
| | |
| At [[atmospheric pressure]]s, when a liquid's vapor pressure increases with increasing temperatures to the point at which it equals the atmospheric pressure, the liquid has reached its [[boiling point]], namely, the temperature at which the liquid changes its state from a liquid to a gas throughout its bulk. That temperature is very commonly referred to as the liquid's ''normal boiling point''.
| |
| | |
| Not surprisingly, a liquid's normal boiling point will be at a lower temperature the greater is the tendency of its molecules to escape from the liquid, namely, the higher is its vapor pressure. In other words, the higher is the vapor pressure of a liquid, the higher is the volatility and the lower is the normal boiling point of the liquid. The adjacent vapor pressure chart graphs the dependency of vapor pressure upon temperature for a variety of liquids<ref name=Perry>{{cite book|author=R.H. Perry and D.W. Green (Editors)|title=Perry's Chemical Engineers' Handbook | edition=7th Edition|publisher=McGraw-Hill|year=1997|id=ISBN 0-07-049842-5}}</ref> and also confirms that liquids with higher vapor pressures have lower normal boiling points.
| |
| | |
| | |
| ''[[Volatility (chemistry)|.... (read more)]]''
| |
| | |
| {| class="wikitable collapsible collapsed" style="width: 90%; float: center; margin: 0.5em 1em 0.8em 0px;"
| |
| |-
| |
| ! style="text-align: center;" | [[Volatility (chemistry)#References|notes]]
| |
| |-
| |
| |
| |
| {{reflist|2}} | | {{reflist|2}} |
| |}
| | </small> |
Latest revision as of 10:19, 11 September 2020
1901 photograph of a stentor (announcer) at the Budapest
Telefon Hirmondó.
Telephone newspaper is a general term for the telephone-based news and entertainment services which were introduced beginning in the 1890s, and primarily located in large European cities. These systems were the first example of electronic broadcasting, and offered a wide variety of programming, however, only a relative few were ever established. Although these systems predated the invention of radio, they were supplanted by radio broadcasting stations beginning in the 1920s, primarily because radio signals were able to cover much wider areas with higher quality audio.
History
After the electric telephone was introduced in the mid-1870s, it was mainly used for personal communication. But the idea of distributing entertainment and news appeared soon thereafter, and many early demonstrations included the transmission of musical concerts. In one particularly advanced example, Clément Ader, at the 1881 Paris Electrical Exhibition, prepared a listening room where participants could hear, in stereo, performances from the Paris Grand Opera. Also, in 1888, Edward Bellamy's influential novel Looking Backward: 2000-1887 foresaw the establishment of entertainment transmitted by telephone lines to individual homes.
The scattered demonstrations were eventually followed by the establishment of more organized services, which were generally called Telephone Newspapers, although all of these systems also included entertainment programming. However, the technical capabilities of the time meant that there were limited means for amplifying and transmitting telephone signals over long distances, so listeners had to wear headphones to receive the programs, and service areas were generally limited to a single city. While some of the systems, including the Telefon Hirmondó, built their own one-way transmission lines, others, including the Electrophone, used standard commercial telephone lines, which allowed subscribers to talk to operators in order to select programming. The Telephone Newspapers drew upon a mixture of outside sources for their programs, including local live theaters and church services, whose programs were picked up by special telephone lines, and then retransmitted to the subscribers. Other programs were transmitted directly from the system's own studios. In later years, retransmitted radio programs were added.
During this era telephones were expensive luxury items, so the subscribers tended to be the wealthy elite of society. Financing was normally done by charging fees, including monthly subscriptions for home users, and, in locations such as hotel lobbies, through the use of coin-operated receivers, which provided short periods of listening for a set payment. Some systems also accepted paid advertising.
