FLU
454
I< L U
r
deed makes it boil more rapidly, but does not increase its tempe-rature. This was first observed by Dr. Ilooke. It was observed,when treating of the melting point of solids, that it is capable ofbeing varied considerably bv altering the situation of the body.Thu-, water may be cooler! down considerably lower than 311°,a Unout freezing The boiling point is still less fixed, dependingentirely on the degree of pressure to which the liquid to be boiledis exposed. If we diminish the pressure, the liquid boils at alower temperature; if we increase it, a higher temperature is ne-cessary to produce ebullition. From the experiments of professorRobison, it appears that, in a vacuum, all liquids boil about 143°lower than in the open air under a pressure of 30 inches of mer-cury ; therefore water would boil in vacuo at 67°, and alcohol at34°. In a Papin’s digester, the temperature of water may be raisedto 300°, or even 400°, without ebullition: but the instant that thisgreat pressure is removed, the boiling commences witii prodigiousviolence. The elasticity of all the elastic fluids into which liquidsare converted by heat, increases with the temperature; and thi-vapour formed, when the liquid boils in the open air, possesses anelasticity just equal to tliat of air, or capable at a medium of ba-lancing U column of mercury 30 inches high. The following veryimportant table, drawn up by Mr. Dalton from his own experi-ments, exhibits the elasticity"of steam, or the vapour of water ofevery temperature, from—40° to 323°. The elasticities of all thetemperatures from 32° to 212° were ascertained by experiment;the rest were calculated by observing the rate at which the elasti-city increased or diminished according to the temperature.
TABLE OF THE ELASTICITY OF STEAM.
Temperature.
| Force ot Vap.
i in inches of
V
"rt
t-
o
C.
£
V
H
Force of Vap.in inches ofMercury .
U
rt
o
a.
V
** <r> >•,!
?_£ S|
u o £ !
P s u i
t-<
rt
4*
CJ
a.
£
r v
Force ot Vap.in inches ofMercury .
Temperature.
Force of Vap.in inches ofMercury .
—40°
.013
32
.200
70°
.721
108°
2.39
146°
6.70
—30
.020
33
.207
71
.745 -
109
2.46
147
6.87
—20
.030
34
.214
72
.770 .
110
2.53
148
7.05
—10
.043
35
.22!
73
.7.96, :
111
2.60
149
7.23
—
36
.229
74
.823 !
112
2.68 |
150
7.42
0
.064
37
.237
75
.851
113
2.76 ■
151
7.6l
1
.066
38
,245
76
.880 1
114
2.84 ;
152
7.81
2
.068
39
.254
77
.910 1
1 15
v.yi i
153
8.01
3
.071
40
.263
78
.940 ;
116
3.00
154
8.20
4
.074
41
.273
79
.971
117
3.08
155
8.40
5
• 07t>
42
.283
80
1.00 •
118
3.16
156
8.6o
6
.079
43
.294
81
1.04 '
119
3.25 i
157
8.81
rr
4
.082
44
.305
82
1.07 j
120
3.33
158
9 02
8
.085
45
.316
83
1.10 !
121
3.42 1
159
9.24
y
,087
46
.328
84
1.14 •
122
3.50
160
9.46
to
.090
47
.339
85
1.17 :
123
3.59 '
161
9.68
ii
.093
48
.351
86
1.21 :
124
3.69
162
9.91
12
:oyr>
49
.363
87
1.24 j
125
3.79
163
10.15
13
.100
50
.375
88
1.28 j
126
3.89
164
10.41
14
.104
51
.388
89
1.32 j
127
4.00
165
10.68
15
.108
52
.401
90
1.36 !
128
4.11 111 66
10.96
16
. 112
53
.415
91
1.40
129
4.22
i 167
11.25
17
.116
54
.429
92
1.44
130
4.34
;!6S
1 1.54
18
.120
1 55
.443
93
1.48
131
4.47
;169
11.83
10
.124
1 56
.458
94
1.53
132
4.60
1170
12.13
20
.129
1 57
.474
95
1.58
133
4.73
|l71
12.43
21
. 134
1 58
.490
96
1.63 1
134
4.86
1172
12.73
' 22
,I3‘>
: .•><»
.507
97
1.68 !
135
5.00
'173
13.02
23
i .144
1 60
.524
1 98
1.74 1
136
5.14
'174
13.32
24
.150
: til
.542
1 99
1.80
137
5.29
[4 75
13.62
25
.156
1 62
.560
100
1.86
138
5.44
,176
13.92
26
.162
63
.578
101
1.9 2
139
5.59
177
14.22
27
.168
! 64
.597
102
1418
140
5.74
1178
1 1.52
28
.174
! 65
.616
103
2.04
141
5.90
179
14.83
2y
.180
■ 66
.635
104
2.11
142
6.05
ISO
15. 15
30
.186
1 67
.655
105
2.18
143
6.21
181
15.50
31
.193
68
.676
106
2.25
144
6.37
182
15.86
—
69
.698 l
107
2.32
145
6.53
183
16.23
6*
1
u«
Cj
-'o .jsi s
V
3
V
*■
,-i
= § cj
y u v
ii 5 fc 1
S-saj
Temperature.
i
Force ot Vap.
0J
3
0/
a-
5
V
> O-W </> C ,o_g C
8 g g
I'iSI
O
5
QJ
r C
| Force of Vap.
in inches of
184°
16.61
213°
30,60 |
242°
51.34
271°
78. S9
300°
11 LSI
185
17.00
214
31.21 I
943
52.18
272
793)4
301
112.98
186
17.40
215
31.83
-244
53.03
.'73
80.98
302
114.15
187
17.80
216
32.46 :
245
53-88
274
82.01
303
115.32
188
IS.20
217
33.09 1
246
54.68
275
83.13
304
116.50
189
18.60)
218
33.72 i
247
55.54
276
84.35
305
117.68
190
19.00 j
219
34.35 !
248
56.42
277
85.47
306
118.86
191
19.42 1
220
34.99
249
57.31
278
86.50
307
120.03
192
19.86 j
221
35.63 ,
250
58.21
2T9
87.63
308
121.20
193
20.3-2 I
ijOO
36.25 :
251
59-12
280
88.75
309
122.37
194
20.77
.23
36.88 ’
252
60.05
281
89.87
310
123.53
195
21.22 1
224
37.53
253
61.00
282
90.99
311
124.69
196
21.68
225
38.200
354
6192
283
92.11
312
125.85
197
22.13
226
38.89
255
62.85
984
93.23
313
127.00-
198
22.69
227
39.59 ,
256
63.76
94.35
314
1 ~’S. 15
199
23.16
22!4
40.30 i
7
64.82
286
95.48
315
129.29
200
y3.(>4
279
41.02 j
258
65.78
287
96.64
316
130.43
201
24.12
230
41.75 ■
259
06.75
288
97.SO
317
131.57
202
24.61
231
42.49 i
260
67.73
289
98.90
318
132.72
203
25.10
232
43.24 i
261
68.72
290
100.12
319
133.86
204
25.61
233
44 no j
262
69.72
291
101.28
320
135.00
205
26.13,
1234
44.78 1
263
70.73
292
102.45
321
136.14
206
26.66
235 -
45.58
264
71.74
293
103.63
322
137.28
207
27.20
>36
46.39
265
72.76
294
104.80
323
138.42
208
27.74
237
47.20
73.77
295
105.97
324
139.56
209
28.29
238
48.02
267
74.79
296
107.14
325
140.79
210
28.84
239
48.84
268
75.80
297
108.31
211
29.41
240
49-67
269
76.82
298
109 48
212
30.00
241
50.50
270
77.85
1299
110.64
Mr. Dalton has discovered that the elasticity of every oilier va-pour or steam is precisely the same with that of the steam of wa-ter at the same distance from its boiling point. Tims water boilsat 212°; its elasticity at the temperature of 182°, or 30 under itsboiling point, we see from the table is 13.8(5. Alcohol boils at176°; the elasticity of the steam of alcohol at 14G", or 30° underits boiling point, is .likewise 15.S6. This very important disco-very enables us to ascertain the elasticity of the vapours of all li-quids whatever at any temperature, provided their boiling pointsare known. We have only to find how many degrees the tempe-rature at which the elasticity required is distant from the boiling,point of this liquid. The same number of degrees, added to orsubtracted from 212°, gives us a temperature, opposite to which inthe above table we shall find the elasticity required. Such are thephenomena of the conversion of liquid into elastic fluids. Dr.Black applied his theory of latent heat to this conversion withgreat sagacity ; and demonstrated, that it is owing to the verysame cause as the conversion of solids into liquids ; namely, to thecombination of a certain dose of caloric with the liquid, withoutany increase of temperature. The truth of this very importantpoint was established by the follow ing experiments :
First. When a vessel of water is put upon the fire, the watergradually becomes hotter till it readies 212° ; but afterwards itstemperature is not increased. Now caloric must be constantlyentering from tile fire and combining w ith the water. But as thewater does not become hotter, the caloric must combine with thatpart of it which flies off in the form of steam ; but the temperatureof the steam is only 212°; therefore the caloric combined with itdoes not increase its temperature. We mud conclude, then, thatthe cliange of water to steaui is owing to the combination of tb |Scaloric; for it produces no oilier change. Dr. Black put somewater in a tin-plate vessel upon a red-hot iron. The water was otthe temperature 50°; in four minutes’it began to boil, and in 2Uminutes it was all boiled off. During the first four minutes itreceived 162°, or 40 £ per minute. If we suppose that it receivedas much per minute during the whole process of boiling, the ca "loric which entered into the water and converted it into steamwould amount to 4<)£ X 20 = 810°. This caloric is not indicab^by the thermometer, fur the temperature of steam is only -1* 'therefore Dr. BLck called it latent heat.