A manual of chemistry : on the basis of Dr. Turner's Elements of chemistry : containing, in a condensed form, all the most important facts and principles of the science designed for a text book in colleges and other seminaries of learning / by John Johnston.

  • John Johnston
Date:
1846
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Licence: Public Domain Mark

Credit: A manual of chemistry : on the basis of Dr. Turner's Elements of chemistry : containing, in a condensed form, all the most important facts and principles of the science designed for a text book in colleges and other seminaries of learning / by John Johnston. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    condensed, and descends to the earth in the form of rain. Rain, it is well known, never falls unless the sky is cloudy, nor unless that peculiar kind of dense black cloud appear known by the name of rain-cloud; but the manner in which rain is formed, though different theories have been proposed to account for it, must yet be considered as involved in obscurity. All the accumulations of water upon the surface of the earth are thus subjected to a constant natural distillation; the impuri- ties with which they are charged remain behind, while the pure water in the form of vapor rises in the air to be again diffused over the earth. 117. Constitution of the Gases with respect to Heat.—Recent experiments by Faraday, Thillorier, Mitchell, and others, ap- pear to justify the opinion that gases are merely the vapors of extremely volatile liquids. Most of these liquids, however, are so volatile that their boiling point, under the atmospheric pres- sure, is lower than any natural temperature; and hence they are always found in the gaseous state. By subjecting them to a great pressure, their elasticity is so far counteracted that they become liquid ; and by reducing the temperature of the liquids very low, several of them have even been congealed. Fj ]0 The usual method of liquefy- ing a gas is to put the materials for preparing it into a strong glass tube, keeping them apart if necessary, and then sealing the tube hermetically, or closing it with a cap* and some strong cement. The substances may then be brought together and heat applied if necessary; and the gas as it is generated being unable to escape, when sufficient pressure is produced, is converted into a liquid and collected in the upper part of the tube. These experiments are attended with danger from the bursting of the tubes, and should never be attempted but with the utmost caution. In some cases it will be found most convenient to use straight tubes ; but in others it will be best to have them bent as in the figure. Different gases require very different forces to compress them into the liquid form, for while sulphurous acid gas, at the temperature of 45°, re- quires only two atmospheres, carbonic acid gas at 32° requires no less than thirty.six atmospheres. 120. Carbonic acid, as well as several other of the gases, have been solidified; which is done by exposing them, in the liquid state, to the action of intense cold. To prepare solid carbonic acid, it is necessary to construct a very strong apparatus with a generator to receive the materials for forming the liquid acid, and a smaller receiver, into which this liquid is * Dr. Torrey.