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No experiments were made with crystals belonging to the regular system, on account of the difficulty of procuring suitable specimens. It is probable, however, that in media of this nature, the isothermal surfaces would be spherical. T

Conducting Power of Liquids. When heat is communicated to the bottom of a liquid, it diffuses itself quickly and uniformly throughout; not, however, by conduction, i.e. by radiation from particle to particle, but in consequence of currents in the liquid itself,—the lower portion, which is heated and thereby expanded, ascending, while the colder and heavier portion sinks. The communication of heat from the upper to the lower part of a liquid takes place so slowly, that Rumford absolutely denied the existence of conducting power in bodies of this class; it has, however, been shown to exist in them by Thomson, Murray, and Dalton (Gilb. 14, 129, 158, and 184*); and, according to Despretz, the conduction of heat in liquids takes place according to the same law as in solids. -Respecting the supposed slower cooling of warm mineral waters, vid. Longcha

(Ann. Chim. Phys. 24, 248), Schweigger, Reuss, and Seiler (Schw. 39, 386), L. Gmelin (Pogg. 7, 451), Kastner (Kastn. Archiv. 13, 408; 18, 489), Wanderlich (Wirtemb. med. Correspond. Blatt. 1837, 457), Chevalier (J. Chim. med. 12, 37).

The cooling of heated bodies in the air and in gases is due, partly to the radiation which takes as it would in vacuo, partly to the immediate transference of heat to the particles of air surrounding the bodies. The latter mode of communication is not affected either by the nature of the surface or by the absolute temperature, provided the difference of temperature between the heated body and the surrounding air remains the same; so long as the elasticity of the air continues unaltered, its density may vary in any way whatever from change of temperature, without producing any alteration in the rate of cooling. On the other hand, the velocity of cooling by contact varies: 1. With the elasticity of the several kinds of gas-inasmuch as the diminution of elasticity consequent on mechanical rarefaction lessens the rate of cooling in a proportion which is different in the different kinds of gas; 2. According to the nature of the surrounding gas—being greatest in hydrogen (whether from the greater mobility of that gas or its greater capacity for heat ?) less in olefiant gas, still less in air, still less in carbonic acid, and, according to Davy (Schw. 20, 153), (slowest of all in chlorine gas. (Similar results are given by Dalton in his New Syst. 1, 114.) But even when the actual velocity changes, the law of cooling by contact of gas remains always the same, viz., that when the difference of temperature is doubled, the velocity of cooling increases 2.35 fold. (Petit and Dulong.) Comp., Despretz (Änn. Chim. Phys. 6, 184), and Prevost (Mém. de la Société de Genève, 4, 265). -Disturbance of the air accelerates the rate of cooling.-The observation of Böckman that metals cool more quickly, and charcoal, earthy sub.. stances, and liquids more slowly, when heated in the sun than when heated in the sand-bath, deserves further investigation.

6. Heat which enters into bodies expands them. This expansion varies greatly according to the nature of the substance, not only in degree, but also in the law which it follows. * Thomson, Nicholson's Phil. Journ. vol. 4, p. 529 f. Murray

vol. 1, p. 165 and 241.
Dalton, Memoirs of the Society of Manchester, vol. 5, part II. p. 373 f.

All gases and vapours, e.g., common air, oxygen, hydrogen, nitrogen, carbonic acid, hydrochloric acid, and sulphurous acid gas, and ether vapour expand when heated from 0° to 100° C. by 0.375 of their volume, according to Gay-Lussac and Dalton, and from 0-364 to 0.365 according to Rudberg. The latter determination gives an expansion of za for each degree centigrade (or for each degree Fal.); that is to say, 274 cubic inches of air at 0° become 275 c. i. at + 1°, 276 c. i. at 2°, and 375 cubic inches at 100°; at 274o their volume is doubled, at 548 it is trebled, and so on. On the contrary, 274 measures of any gas at 0° suffer a contraction of 1 measure for each degree of cooling. 274 measures of gas at 0° contract at 20° to 254 measures, and expand at + 30° to 304, at + 80° to 354, and at + 100° to 574 measures. Hence the volume of a gas measured at any given temperature may be reduced to the volume which it would have at any other temperature; e. g. given 1000 measures at – 14°: required the volume at 0°?—(274 – 14): 274 = 1000 : x= 1053.8. Given 1000° measures at + 36° : what is the volume at 0? (274 + 36): 274 = 1000 : x = 884.–Given 1000 measures at 27° : what will be the volume at 100°? (274 + 27):(274 + 100):: 1000 : x = 1242.5.—Even when the heat is increased to 300° C. the expansion of different gases, as of air and hydrogen, is exactly the same. (Petit and Dulong.)—The expansion of atmospheric air when heated from 0° to 100° is constantly the same, whether it be subjected to a pressure of is, š, , 1, 1, 2, 3, 6, or 15 atmospheres. (Davy, Phil. Transact. 1823, 204.—Common air, heated from 100° to low redness, expands from 1 measure to 2:25, and at a bright red heat to more than 2.50 measures. (Davy.)--According to Muncke, vapours heated to their boiling point expand much more strongly than air.

The more recent experiments of Magnus and Regnault have shown that the coefficient of expansion is not exactly the same for all gases. The differences, however, are not very considerable, as will be seen from the following table, which gives the expansions of the different gases examined by these philosophers, between the temperatures of melting ice and boiling water.

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Hence it appears that the expansion of air for each degree centigrade is equal to 0.003665 of the bulk at 0° C.; this gives 0·00204 or aço for each degree of Fahrenheit's scale.—Regnault also found that for atmospheric air, carbonic acid, and sulphurous acid, the coefficient of expansion increases with the tension of the gas.

The laws commonly admitted,—viz. that the expansion of any gas between given limits of the temperature is independent of the initial density; and that all gases have the same coefficient of expansion--are regarded by Regnault as true in the limit only; that is to say—they accord more and more nearly with the results of observation in proportion as the gases are in a more expanded state. 1.

Liquids heated from 0° to 100° C. expand as follows. Water...

0.0466

0.0200 Dalton Saturated solution of salt

0.0500

0.01887 Cavendish Oil of vitriol

0.0600

0.01848 Lavoisier and Hydrochloric acid (sp. gr. l•137) 0:0600

Laplace Nitric acid (sp. gr. 1:40)

0:1100 Mercury 0.01818 Hallström Alcohol (sp. gr. 0·817).

0:1100

0.01801 Shuckburgh Ether ..

0.0700

0.01800 Petit and Dulong Oil of turpentine

0.0700

0.01786 Deluc Fat oil

0.0800

0.01695 Roy.

Dalton.

100 measures of liquid carbonic acid at 20° expand to 150 measures at + 30. [Such at least is the case according to the assertion of Thilorier (Ann. Chim. Phys. 60, 427), that the sp. gr. of this acid is 0.90 at – 20°, 0.83 at 0°, and 0.60 at + 30°; but at the same time he says: 100 measures of the acid at 0° give 145 measures at + 30, which is inconsistent with the above]. It is certain, however, that the expansion of liquid carbonic acid is much greater than that of gases. Likewise, sulphurous acid and cyanogen in the liquid state expand much more strongly than other liquids, but not so much as carbonic acid. (Kemp.)

Water, when gradually heated from its freezing point, contracts at first, and does not expand till its temperature has been raised somewhat higher. If, therefore, it be at the particular temperature at which its density is the greatest, it will expand, whether heat be added to or abstracted from it. This point of maximum density is placed by Dalton at 2 22° C., by Blagden & Gilpin and by Gay-Lussac at 3.89° (39° Fah.), by Hällstrom at 3:9° (Pogg. 34, 220), Charles at 3:99°, Despretz at 4°, Hope at 4:35o, Lefevre, Gineau and Rumford at 4:44°, by Crichton at 5.55°, and by Playfair & Joule at 39.101° Fah., or 3.95° C. (Chem. Mem. 3, 204.) The apparent maximum density of water enclosed in glass vessels is not attained, according to Dalton, till 5-55°, because the vessel expands when its temperature is raised from 0° to 4°. (For Hällstrom's table of the density of water at different temperatures, vid. Ann. Chim. Phys. 28, 56.)

All aqueous solutions of salts and similar substances have likewise, according to Despretz, a maximum of density. This maximum is situated so much the more below 4° as the solution is richer in salt, and generally even below the temperature at which the solution freezes when agitated; whilst the liquid, when at rest, may be cooled below the point of maximum density without assuming the solid form. Solutions of 3.759 parts of the following substances in 100 parts of water bave their maxima of density and their freezing points when agitated situated at the following temperatures:

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q The expansion of liquids bas lately been further investigated by M. Isidore Pierre: the results of his experiments are contained in a series of memoirs published in the Annales de Chimie et de Physique, 3" sér. The following table contains the true and mean coefficients of expansion of

VOL. I.

Q

the several liquids examined. The expansions being expressed by formulæ of the form

V = 1 + at + bt? + ct: in which t denotes the temperature, and a, b, c are constants to be determined by observation for each particular liquid, -the true coefficients for each temperature are calculated by the formula

d V
dt

= a + 26 t + 3 cť? and the mean coefficients by the formula

V. - V.

= a + bt +

Substances.

Temperatures.

True coefficient.

Mean coefficient.

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35.0

0.0 63.0

0:0 100.0 131.8 30.0

0.0 78.3 30.0

0:0 40.7

0:0 13.0 30.0

0:0 70.0 35.0

0:0 43.8

0.0 102:1

0.0 119.0 400

0.0 74.14 30.0

0.0 59.5

0:0 78.34

0:0 100.0 175.3 30.0

0.0 133.81 25:0)

0:0 11504 25.0

0.0 136.0 - 40.0

0.001 109 738 0.001

141

901 0.001 185 570 0.001 491 250 0.001 329 747 0.000 890 011 0.001 339 328 0.001 068 560 0.001 606 382 0.001 164 842 0.000 944 782 0.000 997 311 0.001 048 630 0.001 347 576 0.001 195

509 0.001 290 277 0.001 269 422 0.001 337 628 0.001 540 060 0.001 448 731 0.001 415 206 0.001 559 038 0.001 493 693 0.001 018 046 0.001 088 924 0·001 142 251 0.001 480 311 0:001 263 687 0.001 085 098 0.001 164 759 0·001 199 591 0.001 446 938 0.001 327 135 0.001 239 896 0.001 776 201 0.001 440 012 0.001 202 792 0.001 534 408 0.001 439 571 0.001 029 103 0.001 142 608 0.001 258 496 0.001 719 623 0.001 489 001 0·001 132 859 0.001 232 491 0·001 295 954 0.001 687 434 0.001 484 159 0.001 128 619 0.001 589 242 0.001 307 358 0:000 847 205 0.001 008 780 | 0.000 916 249 0·001 149 896 0.000 986 237 0.000 925 8540.000 951 664 0.000 979 073 0.001 333 2990:00) 140 338 0.001 101 490 0.001

945 0.001 132 801 0.001 647 378 0.001 338 953 0.000 876 944 0.000 909 479 0.000 942 559 0.001 357 899 0·001 142 034 0.001 272 1350.001 272 094

Acetic ether.

Acetic methyl-ether

Terchloride of phosphorus ..
Terbromide of phosphorus

Terchloride of arsenic..

Bichloride of tin

113

Bichloride of titanium..

Chloride of silicium..

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It will be seen from this table (1) that for all the above liquids, both the mean and true coefficients of expansion increase with the temperature; (2) that for temperatures above 0° the true coefficient is greater than the mean, whereas below 0° it is less; (3) that the true coefficient increases more rapidly than the mean.

In the following table, the volume of the liquids at their boiling point is taken for unity, and the changes of volume are given for all the liquids at equal distances from their boiling points. At the head of each column is given the boiling point of the liquid, together with the barometric pressure at the time of observation. The results detailed in this table are of especial importance in connection with the equivalent volumes of the several liquids; since, according to Kopp and Schröder, the equivalent volumes of liquids should be compared at temperatures equally distant from their boiling points.

Number of

Acetate of Acetic Butyrate of degrees Wood-spirit Alcohol Fusel-oil below

Methyl Ether Methyl boiling

B. P. 66-30 B. P. 78.30 B. P. 131.80 B. P. 59-50 B. P. 74-14° B. P. 102-1° point.

(bar. 759mm). (bar. 758mm). |(bar.751-26mm) (bar. 761-2mm). (bar. 766-5mm). (bar. 743.9mm). 0 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 5

0.9931 0.9938 0.9932 0.9923 0.9922 0.9924 10 0.9863 0.9878 0.9865 0 9848 0.9846 0.9849 15 0 9796 0.9819 0.9800 0.9775 0.9772 0.9777 20 0.9732 0.9761 0.9737 0.9703 0.9700 0.9706

bok

25
30
35
40
45

0.9669
0.9608
0.9547
0.9488
0.9430

0.9703
0.9646
0.9590
0.9536
0.9482

0.9676
0.9617
0.9559
0.9503
0.9448

0.9633
0.9364
0.9497
0.9131
0.9367

0.9629
0.9559
0.9491
09124
0.9339

0.9636
0.9569
0.9503
0.9438
0.9375

50
55
60
65
70

0-9373
0.9316
0.9260
0.9206

0.9429
0.9377
0.9325
0.9275
0.9225

0.9394
0.9342
0.9292
0.9241
0.9192

0.9304
0-3243
0.9183
0.9124
0.9065

0.9295
0.9233
0.9172
0.9112
0.9053

0.9312
0.9251
0.9192
0.9133
0.9075

Det

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