Sidebilder
PDF
ePub

Inches

ture.

or

ture.

ture,

of

103

is, therefore, a limit to the tension of the vapour, which varics with the temperature, but which, for a given temperature, is

TABLE OF THE ELASTIC FOLCE OF TIIL VAPOUR, independent of pressure.

OF WATER. In order to show that, in a closed space saturated with vapour and containing liquid in excess, the temperature being

ACCORDING TO MR. DALTON.
constant, there is a maximum of tension which the vapour can-
not pass, whatever may be the pressure, we employ a baro-
metric tube immersed in a deep cistern, fig. 81, p. 277, vol. iv,

Tempera-
Tempera- Inches

Tempera- Inches This tube is first filled with mercury, and a quantity of ether

of is passed into the tube sufficient to saturate the barometric chamber; there is then some liquid in excess, and the height

Fahrenheil Mercury. Falirenheit Mereury. Fahrenheit Mercury. of the mercury in the tube is ascertained by means of a scale

32° fixed to the cistern. Now, whether the tube be immersed to

0.200 930

1:48 1530 8.01

33 a greater depth, which tends to compress the vapour; or

0.207 94 1:53 154

8:20 whether it be raised, which tends to expand it, the height of

34 0.214 95 1.58 165

8.40

35 the mercurial column remains constant. The tension of the

0.211 96 1.63

156 8.60

36 0.229 vapour, therefore, remains the same in both cases, since the

97 1.68

157 8.81

37 depression neither increases nor diminishes it. Hence, it fol

0.237 98

1.74

168 9:02

38 lows, that when the vapour contained in a saturated space is

0.245 99

1.80 159 9.24

39 0.264 100 1.86 compressed, a part of it returns to the liquid state; and that

160 9.46 40

0.263 if, on the contrary, the pressure is diminished, a portion of

101

1.92 161 9.68

41 0.273 102 the liquid remaining in excess is vaporised, and the space

1.93
162

9.91

42 0.283 occupied by the vapour is saturated anew; but in both cases,

2-04 163 10.15

43 the tension and the density remain constant. If the space

0.294 104 2:11 164 10:41 44 0.305

105 where the vapour is contained be not saturated, or if it do

2.18 165 10.63

45 not contain liquid in excess, the vapour, when the pressure

0:316 106 2.25 166 10.96

46 increases or diminishes, acts entirely as a gas; that is, so long

0.328 107

2.32 167 11.25

47 as it is not brought up to the point of saturation, its tension

0.339 108 2-39 168

11.54

48 and its density increase with the pressure. Consequently, it

0 351 109

2:46 169 11.83

49 is evident that vapours, in a space not saturated, act according

0.363 110

2-53 170 12:13

50 to the law of Mariotte.

0.375 111 2.60 171 12:43

51 0.388 112 2.68 172 12.73 Tension of the Vapour of Water below the Freezing Point.-In

52 0:401 113 2-76 173 13.02 order to measure the elastic force of the vapour of water below

63 0415 114 2.84 174 13:32 0° Centigrade, Gay-Lussac employed two barometric tubes

54 0:429 115 2.92 175 13.62 filled with mercury and immersed in the same cistern. One

55 0:443 116 3:00

176 13.92 of these, completely freed from air and humidity, was used to

16 0.458 117 3:08 177 14.22 measure the pressure of the atmosphere: into the other a

57 0.474 118 3:16

178 14:52 small quantity of water was introduced, and its barometric 58 0.490 119 3.25 179 14.83 chamber was surrounded with a small jacket, in which was

59 0:507 120 3:33 180 15.15 placed a frigorific mixture. By comparing the heights of the 60 0.524 121 3:42

181 15.50 two barometers when the temperature of the frigorific mixture

61 0:542 122 3:50 182

15 86 stood at different points of the scale, Gay-Lussac found that

02 0:560 123

3.59 183 16.23 in the barometer which contained the water, the depression of

63

0.578 12+ 3.69 184 16.61 the mercury, and consequently the tension of the vapour, were

64 0.597 125 3.79 185 17.00 as follows:

05 0 616 126 3.89 186 17.40 66 0.635 127

4.00 187 17.80

67 Tensions.

0.655 128

188 18.20 Temperatures.

08 0.676

4.22 189 18.60 0:1811 of an inch at 0° Cent. or 32° Fahr.

69 0.698

130 4.34 190 19:00 0.0787

-10
14

70
0.721
131

4:47 191 19.42 0.0331

71 0745 132 4.60 192 19.86 0.0142

-30
-22

72 0.770

133
4.73

193 20-32 73 0.796

134

4.86 194 20-77

7+ Hence it is inferred that, at very low temperatures, there is

0.823 135
5:00

21.22 75 0 851

136 still vapour of water in the air.

5.14 196 21.68 76 0.88

137

5.29 197 22:13 Tension of the Vapour of Water from the Freesing to the Boiling

77 0 910

138

5:44 198 22.69 Point. We shall first give the process adopted by Mr. Dalton,

78. 0910 139 5:59 199 23:16 of Manchester, who died in 1844, in order to determine the

70 0.970 140

5.74 elastic force of the vapour of water from 0° to 100° Centigrade.

200 23.64

80 1.001 141 5.90 He employed two barometric tubes A and B, fig. 188, which

201 24:12 81 1:04.

142 were immersed in an iron vessel full of mercury and placed

6:05 202 24.61

82 1.07 143 6.21 over a furnace.

203 25.10

83 1:10 144 6:37 204 25.61 The barometer B was freed from air and humidity, and in

81 1.14 145

6.53 205 26.13 the barometer A was put a small quantity of water. These

85 1:17 146 6.70 206 26.66 two barometers were kept in a vessel of glass full of water, in

86 1.21 147 6.87 207 27.20 the middle of which was immersed a thermometer t, which

87 1.24

7.05
208

27:74 indicated the temperature of the liquid. By gradually heating

88

7.23 209 28.29 the iron vessel, and consequently the water in the glass vessel,

89 1:32

150 7.42 210 28-84 that which was in the tube was vaporised; and in proportion

9 1.36 151

7.61 211 as the tension of the vapour increased, the mercury was

29:41 91

152 7.81 lowered. Then, by marking degree after degree on the scale

212 30.00

92 E, the depression which took place in the tube A, below the level B in the other tube, Mr. Dalton determined the elastic force of the vapour of water at every point of the thermometer latest experimenters, is reckoned more accurate than that of

The second process, viz, that of M, Regnault, one of the between the freezing and the boiling points, and was the first Mr. Dalton, in which the water in the glass vessel cannot be to construct a table of the same, as follows :

| kept exactly at the same temperature throughout its entira

4.11

129

99

[ocr errors]

-20

[ocr errors]

195

128

148 149

1:40 1:44

length, and the precise temperature of the vapour is not ture, as given by these eminent experimenters, is the follow-
always indicated by the thermometer. M. Regnault modified ing :-
his apparatus by substituting for the glass vessel one made of

E = (1 + .007153 T) 5;
iron-plate, in the bottom of which the two tubes were fixed. in which e, denotes the elasticity of the steam in atmospheres;
In this vessel warm water was poured until it covered the and r, the excess of the temperature above 100° Centigrade.

The same formula adapted to Fahrenheit's thermometer is as
Tig, 183.

follows:

e = (1 + .003974 t) ;;
in which e denotes the elasticity of the steam in atmospheres ;
and t the temperature above 212° Fahrenheit. The following
table is derived from the table given by MM, Dulong and
Arago, in their Report, and it is extended from twenty-four to
fifty-three atmospheres, by calculation, according to the pre-
ceding formula:

[graphic]
[ocr errors]
[blocks in formation]

34 35 36 37 38 39 40 41

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

[ocr errors]

8 9 10 11 12 13

43 44 45 46 47 48 49 50 51 52 53

[ocr errors]

2120.00
3860-94

46978
14 233 .96

392 .86

472.73
250 52
398.48

475 .64
2.1

263.81
403.82

478.46
275 .18
408 92

481 .24
31 285.08

413.96

483.95
293.72
418.46

486 59
41 301 .28

422.96

489.21 5 308 •84

427 28

491 .76 53 314 .24

431 .42

494 27 6 320 .36

435 -56

496 72 6) 326 .26

439.34

499 .14 7 331 70

443 .16

501 50
336 .86
446 82

503.85
341 .96
450 .38

506.16
35078
453.82

508 .40
358 .88
457 .16

510.60
tops of the tubes, and the temperatures were observed at differ-

367 .34
460 .45

512 .80
ent degrees from 0 to 500 * Centigrade. By meaus of an

874 .00
463 64

514 82
agitator
, the different strata of the liquid were constantly mixed

380.66
466 .74

517.08.
with each other, in order to preserve a uniform temperature in
all the parts of thu bath in which the two barometric tubes
were placed. Also a plate of glass
fixed in the sides of the tion of the elasticity of steam above the boiling point, which

The apparatus adopted by M. Regnault for the determina-
iron vessel enabled the experimenter to observe the difference
of the level of the mercury in the two tubes. By this apparar tension of the vapour of water either above or below 100°

we now proceed to describe, admits of the measurement of the
rapour from 0° to 50° Centigrade, but he could not einploy it Centigrade. It consists in boiling water in a close vessel, under
for higher temperatures, on account of the limited extent of | ebullition is effected. Then on the principle ihat at the instant

a known pressure, and in measuring the temperature at which

of ebullition the elastic force of the vapour or steam disengaged Tension of Steam above the Boiling Point.--Two method's have is exactly equal to the pressure which the liquid supports

,
been employed in measuring the elastic force of steam at higher we ascertain the tension of the steam or vapour

and its corre
temperatures than 100° Centigrade, the one by MM. Dulong sponding temperature, which resolves the problem. The
and Arago in 1830 ; the other by M. Regnault in 1844. The apparatus is composed of a brass vessel c, fig. 189, hermetically
apparatus of the former experimenters consisted of a boiler of closed and filled with water to about one-third of its capacity.
verythick iron-plate, capable of holding 80 litres, or about Four thermometers are inserted in the cover; two immersed
179 imperial gallons. Two gun barrels, closed at their lower in the upper strata of the liquid, and the other two in the
extremity, were immersed in the water of the boiler, to the sides lower strata. From the reservoir c, proceeds a tube A B, which
of which they were firmly fastened. Each barrel was filled with is adapted to the orifice of a glass globe, having the capacity
mercury, and contained a thermometer intended to show the of twenty-four litres, or 5:28 imperial gallons, and filled with
temperature of the water and of the steam in the interior of air. The tube a B is surrounded with a jacket D, in which
the boiler. In order to measure the tension of the steam, the circulatez a current of cold water, which flows from a reser
boiler was put in communication with a manometer of com- voir E.
pressed air, which had been experimentally graduated. By From the upper part of the globe a proceed two tubes, the
moting degree after degree the temperatures indicated by the one communicating with a manometer of free air o, near the
thermometers

, and observing at the same time the indications apparatus, and the other uu', made of lead, communicating
of the manometer, these experimenters actually measured the with an air-pump, or with a forcing-pump, according as the
tension of steam up to twenty-four atmospheres. They then air in the globe is to be rarefied or compressed ; and the
determined by means of the following formula, temperatures reservoir K, which

contains the globe, is filed with water at
and the pressures of steam as far as fifty atmospheres. These the surrounding temperature.
Tesearches having been made at the instance of the Royal

Suppose now that the first experiments are to measure the
Academy of Sciences of Paris, a report of them was published elastic force of the vapour of water below 100° Centigrade.
in the Memoirs of the Academy," vol. x, 1831. The for- The extremity u' of the leaden pipe is fixed to the platen of
mula which connects the elasticity of steam with the tempera- I the air-pump, and the air in the globe m is rarefied, and conse-

the bath.

[ocr errors]

Pressure

Pressure

in

quently that in the vessel c. Then, by heating this vessel
slowly, the water which it contains enters into a state of ebulli- TABLE OF THE ELASTICITY OF STEAM IN ATMOSPHERES,
sion at a temperature lower than 100° Centigrade, in proportion
to the degree of rarefaction to which the air has been carried; FROM 100% TO 2300-9 cent., ACCORDING TO M. REGNAULT,
that is, the pressure which acts upon the liquid is proportion-
ably less. Moreover, the vapour condensing in the tube AB,
which is constantly kept cooled to the same degree, the pres-
sure originally indicated by the manometer is not increased;

TEMPERATURE,

in

TEMPERATURE. a fact which proves that the tension of the vapour, during the

Atmos.

Atmos,
ebullition, remains equal to the pressure which acts upon the
liquid. Then by consulting on the one side the manometer, Cent.

Fahr.

Cent.

Fahr.
and on the other the thermometers, the tension of the vapour 10000 2120.00 1 1980:8 38984 15
at a known temperature is determined. Again, allowing a 120.6 249 .08

201 .9 395.42 16
little air to enter into the tubes and into the boiler, in order to 133.9 273.02

204.9 400 82 17 increase the pressure, a new observation is made, and so on, 144 0 291 .20 4 207 .7 405 .86 18 until the temperature of 100° Centigrade is attained. In order 152 .2 305 .96 5 210.4 410 72 19 to measure the elastic force of the vapour of water above 1000 1592 318 •56

213.0 415 .40 20 Centigrade, the orifice u is put in communication with a 165 3 329 •54 7 215 5 419.90 21 forcing-pump, by means of which the air of the globe and of the 170 .8 339.44 8 217 .9 424 .22 22 boiler are subjected to successive pressures greater than that 175.8 318 44 9 220 .3 428 54 23 of the atmosphere. Thus the boiling of the water is retarded, 180 .3 356 -54 10 222 5 432 .50 24 and the simultaneous observation of the manometer and the 184 5 364 .10 11 224 .7 436 46 25 thermometers shows the tension of vapour at temperatures 188.4 371 .12 12 226 .8 440 .24 26 higher than 100° Centigrade. The experiments of M. Regnault 192.1 377 .78 13 228.9 444 .02 27 being among the latest that have been published, it will be 19.5.5 383.90 14 230 .9 447 62 28 useful to add here a table of the results at which he has arrived.

[graphic][subsumed][ocr errors][subsumed][subsumed][subsumed][ocr errors][ocr errors][ocr errors]
[blocks in formation]

Fahr. --22° -13

4 6 14 23 32 41 50 59 68 77 86 95

0.014 0.022 0.033 0.051 0.077 0.118 0 181 0.257 0.361 0.500 0 685 0.935 1.242 1.647

Ceut.
40°
45
50
55
60
65
70
75
80
85
90
95
100

Fahr.
1040
113
122
131
140
149
158
167
176
185
194
203
212

2:162 2.811 3621 4.625 5.858 7.360 9.210 11:359 13.963 17.049 20.687 21.953 29.922

These tables show that the elastic force or pressure of the yapour of water and steam increases according to a certain law more rapidly than the temperature; but this law is not yet clearly ascertained. The table of M. Regnault differs from that of MM. Dulong and Arago; and, of course, the empirical formula given by these philosophers does not quite apply to the former; by calculation, this formula gives 27-22 atmo. spheres instead of 28, for the temperature of 230o.9 Centigrade or 447°:62 Fahrenheit. Water is the only liquid whose vapour, from its important applications, has engaged the attention of philosophers. The elastic force of the vapours of other liquids has not been determined with accuracy or to any extent. It is known, however, that substances in solution, as salts and acids, at the the same temperature as that of water, diminish the elastic force of the vapour of such mixtures, and this diminution increases in proportion as the solution becomes more concentrated ; for ebullition then takes place only at & higher temperature. The following table will show the boil. ing points of water mixed with salt in certain proportions up to the point of saturation.

10 16 20

30 35

[ocr errors][ocr errors][ocr errors]

do. do.

[merged small][ocr errors]

1

[merged small][ocr errors]

vacuum.

Fig. 190.

TABLE OF THE BOILING POINTS OF WATER of this liquid be the same in both tubes. The globe and its
HOLDING SALT IN SOLUTION.

stop-cock are now removed, and in their place is put the
Mixtures,

Proportions of Salt. Boiling Points. funnel c, furnished with a stop-cock a, which differs in its
Pure water,

No parte,

2120.0 construction from the ordinary stop-cocks. It is not pierced
Sea water,
1 part in 33,

213 2 through and through, but has only a small cavity as seen at o
Saline solution, 2 parts in 33, 214 .4 on the right of the figure. Having poured into the funnel o
do.
3 do.

215 5

the liquid which is to be vaporised, having marked the level
do.
4 do.

2167

I of the mercury and opened the stop-cock b, the stop.cock a
do.
6

217 .9

is then turned in such a manner that the cavity is filled with
do,
6

219 .0

the liquid; it is then turned again, so that the liquid may
do.

7
do.

2:20 2 enter the space a, and there be vaporised. Thus the liquid is
do.
8 do.

221 4

made to enter, drop by drop, until the air in the tube is saturated
do.
9 do,

222 5

with vapour, which is ascertained by the level 1 ceasing to

descend.
do,
10 do,
223 •7

As the tension of the vapour produced in the space
do.
11 do.

224 9

A is added to that of the air already there, the volume is
Saturated water 12 do.

226 0

increased; but it is easily reduced to its original volume, by

pouring an additional quantity of mercury into the tube B. Misture of Gases and Vapourë – The following are the laws | When the mercury is by this means made to rise in the large which regulate the mixture of gases and vapours :

tube to the level i which it had at first, there is observed in the ist. The tension and consequently the quantity of the tubes B and A a difference of level B 0, which evidenıly reprevapour which saturates a given space are the same, at the sents the tension of the vapour which' has been produced ; for same temperature, whether this space contains a gas or is a the air having resumed its original volume, its tension is not

changed. Now if some drops of the same liquid which was
2nd. The elastic force of the mixture is equal to the sum of introduced into the space A be passed into the barometric
the elastic forces of the gas and the vapour mixed together, vacuum, a depression 'exactly equal to Bo is observed; and
the gas being referred to its primitive volume.

this proves clearly that, at the same temperature, the tension of
In order to prove these laws, M. Gay-Lussac employed the a vapour is the same in a gas as in a vacuum.
apparatus represented in fig. 190.

As to the second law, it is proved by the preceding experi-
ment, because when the mercury has resumed its level 1, the
mixture supports the atmospheric pressure which acts at the
top of the tube f, plus the weight of the column of mercury
BO. Now these two pressures exactly represent, the one the
tension of the dry air, and the other the tension of the vapour.
Whence, the second law may be considered as a consequence

of the first. The apparatus which we have described only
2 B

admits of experiments at the ordinary temperature; but M.
Regnault, by means of an apparatus capable of being employed
at different temperatures, has compared the tension of the
vapour of water in air and in a vacuum. He found that it
was always feebler in the former than in the latter case; but
the differences were so trifling, that the law of Gay-Lussac is
not diminished in its generality and value,
Applications. In addition

Fig. 191.
to the well-known applica-
tion of steam, it has often
been proposed to employ
vapours and gases of various
kinds, as a moving power ;
as, for instance, by the ex-
pansion of heated air, or by
the alternate vaporisation
and liquefaction of different
substances, such as ether,
carbonic acid, etc.
be useful, however, to men-
tion here an important prin-
ciple announced for the first
time in 1824, by M. S. Car-
not, in a small but curious
work, entitled Reflexions sur
la puissance mécanique du

fou, ** viz. that the same
It is composed of a glass tube , to the extremities of which quantity of heat can only
are cemented two iron stop-cocks b and d. The lower stop- produce the same amount of labour, whatever may be the
cock is furnished with a short tube, which puts the tube a in

nature of the gas on which it acts, provided that no loss is
communication with a second tube 8 of smaller diameter

. A occasioned by improper or defective arrangements. Experience
scale is placed between these two tubes, in order to measure has fully confirmed the theoretical considerations on which
tube A is then filled with dry mercury, and the
stop-cocks 6 sented a sort of jack or turnspit

, which is very common in
ges

, and furnished also with a stop-cock which is closed. quence of the continual rarefaction of the lower strata which
place of the funnel'c, a glass globe filled with dry air or any other the current of the air which ascends

the chimney in comboy
Next, opening the three stop-cocks, a part of the mercury is it contains, by the heat of the fire. Its mechanism wikish
Hellowed to flow from the tube a, which is replaced by dry air cusciantescribed in the end oss ticular description. This appara.

who papiera
air in the space a expands on issuing from the globe, and is in 1519, and its invention and use probably originated in a
under a pressure less than that of the atmosphere, it is forced much remoter period.
back by pouring some mercury into the tube B, until the level

Reflections on the Mechanical Power of Fire.

[graphic]
[ocr errors]

It may

[ocr errors][ocr errors][ocr errors][ocr errors]

146

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
« ForrigeFortsett »