Elements of chemistry : including the most recent discoveries and applications of the science to medicine and pharmacy, and to the arts / by Robert Kane.

  • Kane, Robert, 1809-1890.
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry : including the most recent discoveries and applications of the science to medicine and pharmacy, and to the arts / by Robert Kane. 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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    ters and summers, of the metallic bars which had imprudently been laid in the masonry of some important public buildings, with the idea of giving additional security, the courses of stone or brick have been loosened from one another, and reconstruction rendered necessary, in order to prevent their being gradually pulled to pieces. In estimating the amount of expansion of a solid body, the great* difficulty is the accurate measurement of the small increase in length which takes place. For this purpose, a great variety of me- chanical arrangements have been constructed. As they are all in principle the same, and the detailed description of any exact form would occupy too much space, it will be sufficient to notice one, which, though not that by which very accurate numbers may be obtained, is calculated to give a very satisfactory idea of their gen- eral construction: a b is the bar of which the expansion is to be determined ; it is fastened securely at the extremity a, and rests at b in a groove along which it is free to move, as in the figure. This end of the bar at b presses against a rod c, which is a lever of the sec- ond order, very near the fulcrum, and this transfers its motion to the end of the lev- er, increased in the proportion of the distance. This lever acts on another similar one, t/, the extremity of which serves as an index on the graduated circular arc e, by which the amount of expansion is re id off. Thus, if the acting lengths of the arms of the levers are respectively 1 and 20, and the end of the bar a at b moves ToVo °f an inch, the end of the index d will move on the scale e 20x20 4 through _fnvkfr!—in °f an inch, a space capable of being divided by a microscope and vernier into 200 measurable spaces, so that an expansion of the two hundred thousandth of an inch can be accu- rately determined. For a popular illustration, the source of heat may he lamps, as in the figure; but for accurate experiments, the bar is completely immersed in a bath of oil or water, and the tem- perature ascertained by a suitable arrangement of thermometers. The most important results thus obtained are the following. The temperature being raised from 32° to 212°, the increase in length of a bar of Glass varies from to . Copper T2?T _ i is no 3*2 Brass 5J Soft iron *-! Steel Gold Silver Lead Tin. r The increase in length is called the linear dilatation of a sub-