File:The panorama of science and art (1823) (14803943783).jpg

Identifier: panoramaofscienc02smit (find matches)
Title: The panorama of science and art
Year: 1823 (1820s)
Authors: Smith, James, 1759-1828?
Subjects: Technology Technology
Publisher: London : Caxton Press
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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he air in theball and upper part of the tube, will expand and drive theliquor into the lower ball, and consequently its surface willdescend ; on the contrary, as the surrounding air becomescolder, that in the ball is condensed, and the liquor, pressedby the weight of the atmosphere, will ascend ; thus the liquorin the tube ascends or descends more or less, according to thestate of the air contiguous to the instrument. To the tube isaffixed a scale of the same length, divided upwards and down-■Wards from the middle, C, into 100 equal parts, by whichn.eans the ascent and descent of the liquor in the tube, andconsequently the variations in the temperature of the atmo-sphere, may be observed. Air-thermometers are in generalconstructed so as to have a range equivalent to a few degreesof Fahrenheit: and they serve to shew slight changes of tem-perature in a very striking manner; on this account it is pro-per to have them in a laboratory, although they are upon thewhole of limited utility.
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1-, -t ,r..l ^, .Tr-fl.:.-, P>i/-/.i^iW ImXnfr,,// /■;\,/,,-ri-r-:r.i\c,;-li.il>.i.i. CHEMISTRY. 323 Apparatus. The Pyrometer. As the common mercurial thermometer cannot be employedto ascertain degrees of heat above 500 or 550 degrees of Fah-renheit, it is totally inapplicable to most of the operations ear-ned on in furnaces and ovens: yet in a variety of manufacturesand chemical operations, success depends upon the adjustmentof the heat with a degree of nicety which the most experiencedpersons are incapable of determining by mere observation.To supply this desideratum, Wedgwood contrived an instru-ment called a pyrometer, the range of which extends to 32,000degrees of Fahrenheits scale, its utility is derived fromtheproperty which clay has of contractino-in proportion to thedegree of heat to which it is exposed. This contraction ispermanent, and a less degree of heat than that which the clayhas experienced, will not alter its dimensions. If, therefor

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