EXP
353
EXP
in bulk when heated, and diminished in bulk by being cooled. IWe may therefore consider expansion as one of the most generaleffects of heat. It is certainly one of the most important, as ithas furnished us with the means of measuring all the others.Though all bodies are expanded by heat and contracted by cold,and this expansion in the same body is always proportional to somefunction of the quantity of caloric added or abstracted ; yet theabsolute expansion or contraction has been found to differ exceed-ingly in different bodies. In general, the expansion of gaseousbodies is greatest of all ; that of liquids is much smaller, and thatof s»lids the smallest of all. Thus, 100 cubic incites of atmo-spheric air, by being heated from the temperature of 32° to that of212’, are increased to 137.5 cubic inches ; while the same augmen-tation of temperature only makes 100 cubic inches of wafer as-sume the bulk of 1.04.3 cubic inches; and 100 cubic inches of iron,when heated from 32° to 212°, assume a bulk scarcely exceeding100.1 cubic inches. From this example, we see that the expan-sion of air is more than eight times greater than that of water,’ andthe expansion of water about 45 times greater than that oi iron.An accurate knowledge of the expansion of gaseous bodies beingfrequently of great importance in chemical researches, many expe-riments have been made to ascertain it ; yet, till lately, the pro-blem was unsolved. The results of philosophers were so variousand discordant, that it was impossible to form any opinion on thesubject. This was owing to the want of sufficient care in exclud-ing water from the vessels in which the expansion of the gases wasmeasured. The heat which was applied converted portions of thiswater into vapour, which, mixing with the gas, totally disguisedthe real changes in bulk wh.ch it had undergone. To this cir-cumstance we are to ascribe the difference in the deteimmationsof iiit Luc,, general Hoy, Saussure, d’lvernois, &c. Fortunatelythe problem has lab ly engaged the attention of Mr. Dalton ofManche-ter, and M.„ Gay La-sac ; and their experiments, madewith the proper precaution-, have solved the problem. Mr. Dal-ton’s experiments are distinguished by u simplicity of apparatuswhich adds greatly to their value, as .t puts it in the pow er of othersto repeat them without difficulty. It consists merely of a glasstube, open at one end, and divided into equal parts ; (lie gas to beexamined was introduced into it alter being propeily dined, andtile tube is idled with mercury at the open end to a given point ;he ,t is then applied, and the dilatation is observed by the quantityOt mercery which is pushed out. Mr. Gay Lussae’s apparatus ismore complicated, lint equally precise ; and as his experiments''ere made on larger bulks of air, their coincidence with those ot-Mr. Da.ton adds considerably to the. confidence which may lieplaced in i] lt . results. From the experiments of these philoso-phers it follows, that all gaseous bodies whatever undergo thesame expansion by tile same addition of heat, supposing themplaced in the same circum-tances. It is sufficient tnen to ascer-tain the law of expansion observed by any one gaseous body, inorder to know the exact rate of dilatation of them ail. Now, fromtin' experiments of Gay I.ussac we learn, that air, by being heatedfrom 32° to 212°, expand from 100 to 137.5 parts ; the increase ofbulk on ISO* is then 37.5 parts ; or, supposing the bulk at 32° tohe unity, the increase is equal to 0.375 parts ; this gives us0.00503, ur-j-Gth part, for the expansion of air for 1° of tire ther-mometer. Mr. Dalton found, that 100 parts of air, by beinghealed from 55° to 212°, expanded to 132.5 parts; this gives us anexpansion of 0.00207, or part, fori"; which differs as littlefrom the determination of Lussac as can he expec ted in experi-ments of such delicacy. From the experiments of Mr. Dalton,>1 appears that the expansion of air is almost perfectly equable ;mat is to say, that the same increase of bulk lakes place by the*»me addition of caloric at all different temperatures. It is true,tndeed, that the rate of diminution appears to diminish as thejetnnerature increases. Thus the expansion from 55° to 133-j*, orfor the first 774 degrees, was 107 parts; while the expansion from133-j to 212°, or for the next 77°4-, was only 158 parts, or 9 partsl p 'S than the first. Rut this difference, in all likelihood, is chieflyapparent; for de Luc has demonstrated that the thermometer i‘s"ot an accurate measure of the increase of heat. From the expe-riments 0 f Gav Lussac, it appears that the steam of water, and theVapour of ethe’r, undergo the same dilatation with air when the sameaddition is made to their temperature. We may conclude then thatall elastic fluids expand equally and uniformly by heat ; and thatvol. ii.-no. 78.
this expansion is nearly equable, though not perfectly so. Thebillowing table gives us the bulk of a given quantity of air at ailtemperatures from 32° to 212°.
Tern.
Bulk.
Tern. 1
Bulk.
Tem.
Bulk.
32°
100000
59°
105616
86°
111232
33
100208
60
105824
87
111440
34
10041G
61
106032
88
11164S
35
100624
62
100240
89
111856
36
100832
63
10644S
90
112064
37
101040
64
106656
91
112272
38
101248
65
106864
92
112486
39
101456
66
107070
93
1126S8
40
101664
67
107280
94
112896
41
101872
68
107488
95
113104
42
102080
69
107696
96
113312
43
102288
70
10790 i
97
113520
44
102496
71
108112
98
113728
45
102764
72
108320
99
113936 -
46
102Q12
73
108528
100
114144
47
103120
74
108730
1 10
116224
48
103328
75
108944
120
118304
49
103536
76
109152
130
130384
50
103744
■ 77
. 109360
140
122464
51
103952
78
109568
150
124541
52
104160
79
109776
160
126624
53
104268
80
109984
170
128704
54
104576
81
110192
ISO
( 1307S4
55
104784
82
110400
190
132864
5t5
104992
83
110608
200
134944
57
105220
S4
110816
210
137024
58
1054 )S
85
111024.
212
137440
The expansion of liquid bodies differs from that of the - elasticfluid--, not only in quantity, hut in the want of unitomiity withwhich they expand when equal additions are made to the tempe-rature of each. This difference seems to depend upon the fixityor volatility of the component parts of the liquid bodies; lor ingeneral those liquids expand most by a given addition ot heat,w ho e boiling temperatures are lowest, or which contain in theman ingredient which readily assumes the gaseous form. Thus mer-cury expands less when l.eated to a given temperature than water,,w hich bo.Is at a heat much inferior to mercury ; and alcohol ismuch more expanded than water, became its boiling temperatureis lower. In like manner nitric acid is much more expanded thansulphuric acid ; not only because its boding point is lower, butbecause a portion of it has a tendency to assume the form of anelastic fluid. We may consider it therefore as a pretty- generalfact, that the higher the temperature necessary to cause a liquid toboil, the smaller the expansion is which is produced by the addi-tion of a degree of heat; or, in other words, the expansibility ofliquids is nearly inversely as their boiling temperature. Anothercircumstance, respecting the expansion of liquids deserves par-ticular attention. 'llie expansibility of every one seems-to in-crease with the temperature; or, in other words, the nearer a li-quid is to the temperature at which it boils, the greater is the ex-pansion produced by the addition of a degree of caloric ; and, onthe other hand, the farther it is from the boiling temperature, thesmaller is the increase of bulk produced by the addition of a de-gree of caloric. Hence it happens, that the expansion of thoseliquids approaches nearest to equability whose boiling tempera--tores are highest; or, to speak more precisely-, the ratio of the ex-pansibility- increases the more slowly, the higher the boiling tempe-rature. These observations are sufficient to shew, that the expan-sion of liquids is altogether unconnected with their density. It-depends upon the quantity of heat necessary to cause them toboil, and to convert them into elastic fluids. But we are alto-rgother ignorant at present of the reason why different liquids re-quire different temperatures to produce this change. The follow-ing table will give the reader a precise notion of the rate of ex-4 X pansion-