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:
1842
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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    stance, but its increase of volume is called the cubical dilatation, and is three times the former. Thus the cubical dilatation of glass is Tinm or *h- Hence a glass ball which holds 428 measures at 32°, becomes capable of holding 429 at 212° ; or if it hold 10-000 at 32°, it holds 10-023 at 212°. In this manner the correction for the expansion of glass is in all cases made. But it is necessary to ap- ply the amount of expansion belonging to the particular sort of glass; thus, in the account of the thermometer in page 51, the cubic dilatation of glass was taken, not as 10-023, but 10-026. [The reason that the cubic dilatation may be taken as equal to three times the linear, without sensible error, is due to the circumstance that the linear dilatation is always a small fraction of the primitive length. If 1+/ represent the dilated length, (1+Z)3, or 1+3 Z-f 3 l*-\-P will be the true volume ; but as / is a small fraction, its triple square and cube may be neglected.] Although it is abundantly proved that solid bodies expand more rapidly at high than at low temperatures, yet, except in the case of some particular substances, as glass, iron, and platinum, whose utility as measurers of heat rendered a knowledge of the law of their expansion necessary, the subject has been little examined ; the degree to which the rate of expansion is affected by temperature will be sufficiently shown in the table which follows. At the temperature of 212° Fahrenheit, as given by an air thermometer, the dilatation for one degree is thus, for Glass. Platinum. Iron. Copper. 1 1 1 1 6 « 6 6 0 6 7 8 6 0 S076O 34120 while at 572° of Fahrenheit it becomes, for Glass. 5 9 2 20 Platinum. Iron. | Copper. 1 6 5 340 1 1 4H6lf|31860 and the temperature deducible from the expansion of a thermometer made of each of these substances should be, in passing from 212° to 572°, as compared with air, Air. Glass. Platinum. Iron. Copper. 572° 667° 592° 702° 623° Platinum expands thus the most regularly of those bodies, and should, therefore, be best fitted for a metallic thermometer. It is remarkable that the rate of expansion is not increased by Tise of temperature for all solid bodies, but, on the contrary in some cases there exists, for solids as for liquids, a point of maxi- mum density, so that the body shall expand whether it be cooled or heated from that degree. This is peculiarly the case in Rose's fusible metal, which has been so often mentioned as a means of ap- plying a steady heat. When heated from 32° to 1110, this metallic alloy increases in volume from 100-000 to 100-830 parts but there the expansion stops, and when farther heated it contracts until when at 156°, the volume is only 99-291, being less than at 32°! By a farther rise of temperature it again expands, and at 178° is at its original volume of 100-000, and continues expanding until being- 100-862 at 201°, almost exactly what it had been at 1110, it Wins to melt. It is curious that it has no point of maximum density when in the liquid state. ^ The different rates of expansion of different solid bodies are sub- servient to some very important uses in the arts and in scientific research. Thus, the difference between the expansibilities of plati num and brass, or any other two metals which differ much mav be used as a very delicate thermometric means. If we take a'flat rule