of a file; into this tube he poured a little water (or any other liquid the subject of experiment,) so as to moisten the whole inside; after this he again poured in mercury, carefully inverting the tube, to exclude all air. The barometer, by standing, sometimes exhibited a portion of water, &c. of one eighth or one tenth of an inch, upon the top of the mercurial column, because being lighter it ascends by the side of the tube; which may now be inclined and the mercury will rise to the top, manifesting a perfect vacuum from air. He then took a cylindrical glass tube open at both ends, of two inches diameter, and fourteen inches in length; to each end of which a cork was adapted, perforated in the middle so as to admit the barometer tube, to be pushed through and to be held fast by them; the upper cork was fixed two or three inches below the top of the tube, and half cut away so as to admit water, &c. to pass by; its service being merely to keep the tube steady. Things being thus circumstanced, water of any temperature may be poured into the wide tube, and made to surround the upper part of the vacuum of the barometer, and the effect of temperature in the production of vapour within can be observed from the depression of the mercurial column. In this way, he says, he had water as high as 155' surrounding the vacuum, but as the high temperature might endanger a glass apparatus, instead of it he used the following one for higher temperatures. Having procured a tin tube of four inches in diameter, and two feet long, with a circular plate of the same soldered to one end, having a round tube in the centre, like the tube of a reflecting telescope; he got another smaller tube of the same length soldered into the larger, so as to be in the axis or centre of it; the small tube was open at both ends; and on this construction water could be poured into the larger vessel to fill it, whilst the central tube was exposed to its temperature. Into this central tube he could insert the upper half of a syphon barometer, and fix it by a cork, the top of the narrow tube also being corked; thus the effect of any temperature under 212° could be ascertained, the depression of the mercurial column being known by the ascent in the exterior leg of the syphon. Mr. Dalton also remarks, that the force of vapour from water between 80° and 212° may be determined by means of an air pump; and the results exactly agree with those determined as above. Take a florence flask half filled with hot water, into which insert the bulb of a thermometer; then cover the whole with a receiver on one of the pump plates, and place a barometer gauge on the other: the air being slowly exhausted, mark both the thermometer and barometer at the moment ebullition commences, and the height of the barometer gauge will denote the force of vapour from water of the observed temperature. This method may also be used for other liquids. It may be proper to observe, that the various thermometers used in these experiments were duly adjusted to a good standard one. After repeated experiments by all these methods, and a careful comparison of the results, he was enabled to digest a table of the force of steam from water of all the tem peratures from 32° to 212.** The only experimental results were the following ones, which are compared with our formula. From these results he determined the ratio belonging to each interval, and filled in the intermediate degrees by interpolation, considering the forces to increase in a geometrical progression. Above 212° he made no trials at that period, though the table was extended to 325°, and has since been found to be erroneous for the temperatures above 212°. 97.-Mr. Dalton afterwards re-examined the subject, and considers from various trials, that the force of steam at 32' cannot be less than 0-2 of an inch; and is most probably 0-25. But with the advantage of having seen the results of Dr. Ure's, and Mr. Southern's experiments, and having made new experiments himself for the temperatures between 2120 and 300°, he gives the following table formed from what he considers the most correct experiments on the subject.+ Nich. Phil. Journal, Vol. VI. p. 263, 8vo. ✦ Annals of Philosophy, Vol. XV. p. 130. for 1820. of a file; into this tube he poured a little water (or any other liquid the subject of experiment,) so as to moisten the whole inside; after this he again poured in mercury, carefully inverting the tube, to exclude all air. The barometer, by standing, sometimes exhibited a portion of water, &c. of one eighth or one tenth of an inch, upon the top of the mercurial column, because being lighter it ascends by the side of the tube; which may now be inclined and the mercury will rise to the top, manifesting a perfect vacuum from air. He then took a cylindrical glass tube open at both ends, of two inches diameter, and fourteen inches in length; to each end of which a cork was adapted, perforated in the middle so as to admit the barometer tube, to be pushed through and to be held fast by them; the upper cork was fixed two or three inches below the top of the tube, and half cut away so as to admit water, &c. to pass by; its service being merely to keep the tube steady. Things being thus circumstanced, water of any temperature may be poured into the wide tube, and made to surround the upper part of the vacuum of the barometer, and the effect of temperature in the production of vapour within can be observed from the depression of the mercurial column. In this way, he says, he had water as high as 155° surrounding the vacuum, but as the high temperature might endanger a glass apparatus, instead of it he used the following one for higher temperatures. Having procured a tin tube of four inches in diameter, and two feet long, with a circular plate of the same soldered to one end, having a round tube in the centre, like the tube of a reflecting telescope; he got another smaller tube of the same length soldered into the larger, so as to be in the axis or centre of it; the small tube was open at both ends; and on this construction water could be poured into the larger vessel to fill it, whilst the central tube was exposed to its temperature. Into this central tube he could insert the upper half of a syphon barometer, and fix it by a cork, the top of the narrow tube also being corked; thus the effect of any temperature under 212° could be ascertained, the depression of the mercurial column being known by the ascent in the exterior leg of the syphon. Mr. Dalton also remarks, that the force of vapour from water between 80° and 212° may be determined by means of an air pump; and the results exactly agree with those determined as above. Take a florence flask half filled with hot water, into which insert the bulb of a thermometer; then cover the whole with a receiver on one of the pump plates, and place a barometer gauge on the other: the air being slowly exhausted, mark both the thermometer and barometer at the moment ebullition commences, and the height of the barometer gauge will denote the force of vapour from water of the observed temperature. This method may also be used for other liquids. It may be proper to observe, that the various thermometers used in these experiments were duly adjusted to a good standard one. After repeated experiments by all these methods, and a careful comparison of the results, he was enabled to digest a table of the force of steam from water of all the tem peratures from 32° to 212.** The only experimental results were the following ones, which are compared with our formula. From these results he determined the ratio belonging to each interval, and filled in the intermediate degrees by interpolation, considering the forces to increase in a geometrical progression. Above 212° he made no trials at that period, though the table was extended to 325°, and has since been found to be erroneous for the temperatures above 212°. 97.-Mr. Dalton afterwards re-examined the subject, and considers from various trials, that the force of steam at 32' cannot be less than 0-2 of an inch; and is most probably 0-25. But with the advantage of having seen the results of Dr. Ure's, and Mr. Southern's experiments, and having made new experiments himself for the temperatures between 212o and 300°, he gives the following table formed from what he considers the most correct experiments on the subject.+ * Nich. Phil. Journal, Vol. VI. p. 263, 8vo. It will appear from this that there is a greater difference between the results of different trials than between the numbers found by our rule and those results, and hence it may be presumed to be nearly true. 98. For the further satisfaction of the reader the principal results of Dr. Ure's experiments shall be given, and his simple and elegant mode of making the experiments described, as in the event of any other species of fluid being found better adapted than water for furnishing vapour the same mode might be usefully adopted to try its force.* |