Elements of chemistry in which the recent discoveries in the science are included and its doctrines familiarly explained : y John Lee Comstock.

  • John Lee Comstock
Date:
1852
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Licence: Public Domain Mark

Credit: Elements of chemistry in which the recent discoveries in the science are included and its doctrines familiarly explained : y John Lee Comstock. Source: Wellcome Collection.

Provider: This material has been provided by the Woodruff Health Sciences Center Library at Emory University, through the Medical Heritage Library. The original may be consulted at the Woodruff Health Sciences Center Library, Emory University.

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    ishcs in proportion to the ascent, and the boiling temperature sinks in proportion as the pressure is removed. 15. Phenomena of boiling on a mountain. — Upon tnis principle is constructed the thermometric barometer, which indicates the elevation of any place above the level of the sea, by the temperature at which water boils at that eleva- tion. By experiment, it has been found that a difference in elevation, amounting to nearly 520 feet, makes a difference of one degree in the boiling point of water. A traveller, therefore, who ascends a high mountain, may ascertain nearly his elevation by the temperature at which he finds his tea-kettle to boil. Thus Saussure found that at a certain station on Mount Blanc, water boiled when heated to 187 degrees. This being 25 degrees less than its boiling point at the level of the sea, allowing 520 feet for every degree, would give an elevation of 13,000 feet. This method can not, however, be very accurate, since the weight of the atmosphere at the same place varies at different times abo'U three inches of the barometric guage. [See Natural Phi- losophy, article Barometer] EVAPORATION. 16. During the process of ebullition, there is a-rapid for- mation of vapor, attended by more or less cor amotion in the liquid. Evaporation also consists in the formation of vapor without heat, but the process is so slow as not to occasion any visible commotion in the fluid. Evaporation takes place, even during the coldest seasons, while ebullition re- quires various' degrees of heat, or at least the removal of atmospheric pressure. To prove that evaporation takes place at ordinary tem- peratures, nothing more is necessary than to expose a quan- tity of water to the open air in a shallow vessel, when the fluid will be found gradually to diminish, and finally to disappear entirely. There is, however, a great difference in the rapidity with which different fluids evaporate, and in general it is found that those whose boiling points are lowest disappear most rapidly. Thus, ether and alcohol evaporate much more rapidly than water. What instrument is constructed on this principle ? How may a traveller, who ascends a high mountain, ascertain nearly his elevation by the boiling of a tea-kettle? What is evaporation? How is it shown that evaporation takes place without the aid of heat? What relation does there seem to be between the boiling point of a fluid and its evaporation?
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