. Edinburgh New Philosophical Journal . On Taking the Dew-point, 177 capillary bore, and an oblong bulb T% to of an inch long, by wide ; a very light and narrow scale, four inches long, and ranging from 100° Fahr. to near zero, is attached from 2^ to 3 inches from the extremity of the bulb ; J and a cork capable of fitting into the neck of the bottle slides on the bare part of the stem. The more similar the circumstances, the more constant the re- sults are likely to be. As the cooling material, equal parts of nitre and sal ammoniac, are employed, the salts being rather finely pounded, well dr
. Edinburgh New Philosophical Journal . On Taking the Dew-point, 177 capillary bore, and an oblong bulb T% to of an inch long, by wide ; a very light and narrow scale, four inches long, and ranging from 100° Fahr. to near zero, is attached from 2^ to 3 inches from the extremity of the bulb ; J and a cork capable of fitting into the neck of the bottle slides on the bare part of the stem. The more similar the circumstances, the more constant the re- sults are likely to be. As the cooling material, equal parts of nitre and sal ammoniac, are employed, the salts being rather finely pounded, well dried, and thoroughly mixed toge- ther ; and a stock of this mixture is kept ready prepared in a close bottle. A little glass tube is provided, capable of holding, when filled to a mark, 40 grains of the mixed salts. This quantity is called a measure of the salts. Another tube is in like manner provided, holding, when filled to a mark, | oz. measure, This is called a measure of water. Suppose, then, that we introduce into the brass bottle one measure of the salts. If we next, taking care that the neck is not obstructed by salt, pour into the bottle very gently one measure of water, at the temperature of the surrounding air, and immediately, but cautiously, introduce the thermometer into the bottle, so that the bulb shall reach the bottom, and the cork fit into the neck, the mercury will fall a few degrees, rarely exceeding five or six; and the farther reduction of temperature we have entirely at our command. By an agitation of the bottle, at first very gentle and cautious, and afterwards slowly and gradually increased, holding it by the upper part of the neck, the farther fall of the thermometer will be so regular and gradual, that we can easily mark the temperature at which the deposition of moisture occurs on the polished external surface of the brass balk With the proportion of salts and water just indicated, we can usually obtain a reduction of temperature of from 15° to 20
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