Elements of chemistry, including the history of the imponderables and the inorganic chemistry of the late Edward Turner / [Edward Turner].

  • Edward Turner
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry, including the history of the imponderables and the inorganic chemistry of the late Edward Turner / [Edward Turner]. Source: Wellcome Collection.

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    The correspondence between the instruments was found to be very exact. Dulong extended the comparison to lower, and to higher temperatures, and inferred that the two instruments agree in their indications from 64*8 to 212°,—but that above the latter point the expansions of the air diminish for successively equal increments of temperature, measured by the mercurial thermometer. Nearly the same results have been deduced by Regnault, excepting that he found the point at which the air thermometer fell behind the mercurial to vary in different instru¬ ments, owing to the difference of expansion of different kinds of glass. In atmospheric air and carbonic acid, he found the expansion, for a given increase of temperature, to be greater as the gas is more condensed. This increase of expansibility, by augmented pressure, was observed in a still more marked degree with cyanogen and sulphurous acid gases. With the latter the dilatation under 1 atmosphere of pressure was 0.3902, and under atmosphere, was 0.3980. These experiments would seem to prove that the increase of expansibility as the pressure is augmented, is most rapid in the cases of those gases which require the least compression for their liquefaction, such as the two last men¬ tioned. Hence Regnault inferred the probability that the vapours, which are even more condensible than these gases, would be found to possess expansibili¬ ties exceeding by a still greater amount that of atmospheric air. Hitherto, how¬ ever, they have been regarded as having exactly the same expansibility, and hence been included in the first of the laws above announced. It is an interesting fact, ascertained in these experiments, that hydrogen gas preserves its expansibility 0.34706, unaltered as high as 3^ atmospheres, the limit to which he carried his experiments on this substance.] ON THE THERMOMETER. The influence of heat over the bulk of bodies is better fitted for estimating a change in the quantity of that agent than any other of its properties ; for sub¬ stances not only expand more and more as the temperature increases, but in general return exactly to their original volume when the heat is withdrawn. The first attempt to measure the intensity of heat on this principle was made early in the seventeenth century, and the honour of the invention is by some bestowed on Sanctorius, by others on Cornelius Drebel, and by others on the celebrated Galileo. The material used by Sanctorius was atmospheric air. There are, however, two forcible objections to the general employment of this ther¬ mometer. In the first place, its dilatations and contractions are so great, that it is inconvenient to measure them when the change of temperature is considera¬ ble ; and, secondly, its movements are influenced by pressure as well as by heat, so that the instrument would be affected by variations of the barometer, thouo-h the temperature should be quite stationary. For the reasons just stated, the common air thermometer is rarely employed; but a modification of it, described in 1804 by Leslie in his Essay on Heat under the name of Differential Thermometer, is entirely free from the last objec¬ tion, and is admirably fitted for some special purposes. This instrument was invented a century and a half ago by Sturmius, Professor of Mathematics at Altdorff, who has left a description and sketch of it in his Collegium Curiosum, p. 54, published in the year 1676 ; but like other air thermometers it had fallen 4
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