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salts; B the quantity of dry salt in 100 parts of the solution (an x denotes that the quantity has not been determined); C shows the boiling point of the solution; Ď the name of the observer (F = Faraday, G Griffiths).

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Oxalic acià

Glauber's salt 31.5 100.6°C. G Borax...
Corrosive sublimate 101.1 G Bisulphate of potash..
Cyanide of mercury 35 101.1 G Sulphate of magnesia
Cryst. verdigris....

16.5 101:1 G Common salt..
Cream of tartar.. 9.5 101.1 G
Nitrate of baryta 26.5 | 101:1 G Nitrate of strontia, .
Sulphate of potash 17.5 101.7 G Neutral tartrate of
Acetate of lead 41.5 101.7 G potash
Nitrate of lead 52.5 102.3
Green vitriol

64 102:3 G Blue vitriol

45 102.3 G Sulphate of nickel. Sulphate of copper 40

102.8

Sal-ammoniac

G and potash Boracic acid .....

103.3 G | Nitrate of potash Chlorate of potash.. 40 103.3 G Ferrocyan. potassium 55 103.3 G

Rochelle salt”.... Oxalate of ammonia 29 103.3 G || Nitrate of soda Carbonate of soda .. 104.4 G Acetate of soda Chloride of barium 45 104.4 G Carb. potash

sat. Alum ..... 52 104.4 G || Potash..

sat. Sulphate of zinc.... 45 104.4 G Nitrat, ammonia. . sat: Oxalate of potash 40 104:4 G

Soda Phosphate of soda.. 105.6 G

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... sat.

Boiling points of aqueous solutions according to Legrand (Ann. Chim. Phys. 59, 423; alsó T. pr. Chim. 6, 56.)— The following table gives the number of parts of each salt dissolved in 100 parts of water: in the first column on the left is given the boiling point corresponding to this proportion. Nitrate of ammonia was employed in the crystallized state, and common phosphate of soda in as dry a state as possible (but not ignited); the other salts in the perfectly anhydrous condition; a is chloride of calcium, b acetate of potash, c nitrate of ammonia, d nitrate of lime, e simple carbonate of potash, f acetate of soda, g nitrate of soda, h chloride of strontium, i nitrate of potash, k sal-ammoniac, l neutral tartrate of potash, m chlorate of potash, n common salt, o chloride of potassium, p ordinary phosphate of soda, q simple carbonate of soda, r chloride of barium. The number under a horizontal stroke gives the boiling point of the saturated solution. This table has a practical value: for by means of it, the quantity of salt in any solution may be found from its boiling point.

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101° 102 103 104 105 106 107 108 109

10.0 16.5 21.6 25.8 29.4 32.6 35.6 38.5 41.3

10.5 20.0 28.6 36.4 43:4 49.8 55.8 61.6 67.4

10:0
20.5
31.3
42:4
53.8
6504
77.3
89.4
101.9

15.0 13.0
25.3 22.5
34.4 31.0
42:6 38.8
50:4 46:1
57.8 53:1
64.9 59.6
71.8 65.9
78.6) 71.9

9.9
17.6
24:1
30.5
36.7
42.9
49.3
55.8
62:4

9.3 18.7 28.2 37.9 47.7 57.6 6707 77.9 88.3

16.7 25.2 32:1 37.9 43:4 48.8 54.0 59.0 63.9

12.2 26.4 42.2 59 6 78.3 98.2 119.0 140.6 163.0

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13-2 13-4 72-5 15-6

18-324-5 13-321-0 104 23-1 31-4

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105

106

1119-5

61-5

35.7 41.3

75 110,

19-6 20-826-2

26-7 32-5 50-3 32 0 38-6 59-4 36-8 44.5 68-141-0 50-3

* 104-5' 25-5 ! 34-6

105

27-7 31-8

37-8 44-2

106

44-7 56-0

47.9 84-2

104.4°: 104.6° :|

60-1 91.5 48-5 105-0

107 108 109 110 111 112 113 114

156-3
176-1
1902
216-8
237-9
259-5
281.6

53.3
59-9
66-4
73.3
80-8
88.1

107 35-8
108 39-7
108-440-2

50-5 106-6° :
56.9 111.6
59.4

115
116

114.2°: 114.7
88.9 296.2

In a similar manner, the boiling point of alcohol is raised by mixing it with water, and that of ether by mixing it with alcohol. (Comp. Magpus, Pogg. 38, 487.)—In like manner, permanent gases combined with water and other liquids require au elevation temperature or diminution of pressure make them escape. In this action an anomaly is observed proceeding from a kind of sluggishness (like that described pp. 9–12), viz., that the gases do not escape at once in the quantities which might be expected under the given circumstances, but that their escape is favoured by agitation or by the immersion of solid bodies, particularly of such as have sharp angles, e. 9., glass rods, wires, metallic filings, silver leaf, sand, sugar-dust. The formation of gas-bubbles appears always to proceed from the solid bodies and from the sides of the vessel, and never from the interior of the liquid, as if the contact of a solid body were essential to the formation of gas. Many solid bodies may however act by means of air adhering to them, which is either itself absorbed by the liquid and drives out the other gas, or else supplies the first bubbles, which then increase in volume by attracting the other gas. (Compare Oerstedt, N. Gehl. 1, 227; Liebig, Ann. Pharm. 30, 13; Schönbein, Pogg. 40, 382.)

Evaporation, Drying, or Desiccation, and in many cases Calcination, Roasting, or Torrefaction are operations the object of which is, for the most part, the separation of a more volatile in the case of evaporation and drying it is a liquid) from a less volatile substance. That these operations proceed most quickly in vacuo will be understood from that which immediately follows.

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a. Time in which it takes place. The rapidity of vaporization is greater, the stronger the affinity of the ponderable body for heat, the higher the temperature, and the less the resistance which the surrounding envelope offers to the expansion of the gas.

In a vacuum vaporization takes place almost instantaneously, whatever may be the nature of the substance: water boils in vacuo at 20°; in so far however as heat is necessary to the production of vapour, the vaporization of the body may be retarded as its temperature gets lower. In a space filled with air or any other gas, vaporization cannot take place instantaneously, unless the substance is capable of producing vapour of great elasticity at the given temperature, and sufficient heat is present for the production of that vapour. Liquid carbonic acid vaporizes almost instantly in the air, to within about of the whole, which solidifies (so that according to Thilorier, 1 gramme of this liquid produces on opening the vessel an explosion as violent as that of 1 gramme of gunpowder); but 346 grains of solid carbonic acid exposed to the air at + 25° lose only 3 or 4 grains per minute, and do not wholly disappear in less than 3 hours (still more slowly when wrapped up in cotton.) (Mitchell.)— The liquid acid already indeed contains a large portion of the heat of fluidity required for its conversion into vapour, and moreover contains a larger quantity of sensible heat, inasmuch as it takes the temperature of the vessels in which it is enclosed,—the solid acid on the contrary must take all its heat from the surrounding bodies. All explosions, detonations, and fulminations arise from a sudden formation of gas brought about by great affinity for heat and a high temperature, the resistance of the surrounding envelope being completely overpowered. Since nitrogen, when it separates from its combinations and assumes the gaseous state, produces the most fearful explosions, even when no great rise of temperature takes place (e. g., in the decomposition of chloride of nitrogen) a peculiarly great affinity for heat must be ascribed to it.

If on the other hand the tension of the nascent vapour is less than the pressure of the external air, so that the vaporization can only proceed by means of the adhesion of the existing gas to that wbich is in course of formation, then-since the portion of air which is in contact with the vaporizing body can only be charged with the nascent vapour in the same proportion as a vacuum-the rate of evaporation will be determined by the rapidity with which the particles of the existing gas are renewed on the surface of the vaporizing body, and will therefore be very slow in a state of rest, but quicker in proportion to the facility with which the existing gas is renewed.

b. Situation in which the formation of Gas or Vapour takes place.

The vaporization of a body takes place in that particular part in which the conditions of vaporization are completely fulfilled.

If a body is very volatile and contains a quantity of heat sufficient to convert it into gas, it instantly assumes the gaseous form throughout its whole mass, as soon as the external pressure allows of such a change. Liquid carbonic acid, sulphuretted hydrogen, and chlorine are instantaneously converted into gas with a kind of explosion, as soon as the vessels containing them are opened.

When a less volatile body is heated from without to increase its tendency to assume the gaseous form, the formation of vapour takes place principally at that part where the heat enters; and when the heating takes place, not from above but from the bottom and sides, and the heated body is liquid, the vapour as it is produced rises in bubbles through the liquid and produces the phenomenon of Boiling or Ebullition. These bubbles of vapour have the peculiar property of being almost always evolved from the surfaces of solid bodies, either the sides of the vessels or bodies floating in the liquid: the edges and angles of such bodies present peculiar facilities for the evolution of gas.

When vaporization takes place only from the surface of a body, either because the heat has access to that part, or because the evolution of gas takes place through the medium of a gas already present, the action can only be recognized by the diminution in bulk of the body; it is then called Evaporation.

e. Absorption of Ileat. As in liquefaction, so likewise in the formation of gas or vapour, the heat which enters into combination with ponderable bodies passes into a state in which it is insensible to the feelings and to the thermometer. Any given substance absorbs the same quantity of heat to form gas or vapour of a given density, whether the vaporization takes place quickly in vacuo or more slowly in a space previously filled with another gas; in the latter case however the reduction of temperature is never so great as in the former, because the heat has more time to enter from without and supply the place of that which has become latent, -and secondly, because the other gas already present gives up a portion of its free heat to that which is being formed-an effect which cannot take place in vacuo.

Solid carbonic acid produces in vacuo, when the external temperature is 30°, a cold of -933°; a pasty mixture of the same with alcohol reduces the temperature to – 92°, and with ether to – 99. (Mitchell.)—Cotton moistened with sulphuret of carbon and wrapped round a thermometer lowers it in vacno from + 16° to -62o. (Marcet.) Liquid sulphurous acid produces in vacuo a temperature of - 60°. (De la Rive, Pogg. 15, 526.) 20 grammes of inercury placed in a watch-glass under the receiver of an air-pump in contact with an equal quantity of liquid sulphurous acid freezes in five minutes. (Bussy.)-If the formation of gas in a space devoid of air be continually renewed by the introduction of a substance which will unite with the vaporized body and form a non-gaseous compound, great degrees of cold may be produced even with substances which are not very volatile. Water placed in a capsule near a basin of oil of vitriol in a vacuum is soon converted into ice; well dried powder of trap-porphyry or oatmeal will produce the same effect as oil of vitriol. (Leslie.) -Āt a temperature of + 15°, Configliachi produced, by surrounding a thermometer with cotton moistened with various liquids and introducing it into a vacuum in which there was also a vessel containing oil of vitriol, with water a temperature of 41.25°, with sulphuric ether – 51°, with alcohol, -37.5°, with nitric ether, – 31.25°, and with hydrochloric ether, - 30°. In the same manner, Graham (Schw. 55, 188) obtained with water a temperature of -14°, and with alcohol (or a mixture of 3 parts alcohol with one part water, which acts equally well because the water renders latent a larger quantity of heat), a temperature of -21°. (Comp. Dove, Pogg. 19, 318.)

Wollaston's Cryophorus (Ann. Phil. 2, 230; also Gilb. 52, 274) consists of two glass bulbs connected by a tube,-exhausted of air and containing a little water. If all the water be made to pass into one of the bulbs, and the empty bulb immersed in a freezing mixture so as to congeal the vapour contained in it, the water in the other bulb will be frozen in consequence of the rapid evaporation which ensues.—Perkin's apparatus for cooling water for household uses by the evaporation of ether, in such a manner that the ether is not lost, acts on similar principles. (Ann. Pharm. 22, 214.)

On opening the stop-cock of an iron vessel containing liquid carbonic acid and directing the stream of vaporizing acid by means of a narrow tube into a hollow sphere, the latter quickly becomes filled with carbonic acid solidified like flakes of snow, the temperature falling to - 100°. The stream directed on the bulb of a spirit-thermometer cools it to – 90°; but it will not freeze more than a small quantity of mercury, whereas the stream of gas produced by a mixture of carbonic acid and ether soon freezes 50 grammes. (Thilorier.) When the liquid carbonic acid is enclosed in a strong glass tube closed with a brass cock and tube, a violent motion of the liquid is observed on opening the stop-cock, of the carbonic acid remains frozen in a dense but yet porous mass, and exhibits at the moment of freezing a temperature of -65°. (Mitchell.)

When a body passes to the gaseous state in a space already filled with another gas, and at temperature at which the tension of the gas in process of formation is less than that already existing, the cold produced is greater—the stronger the tendency of the substance to assume the gaseous form—the greater the quantity of heat required for its conversion—the greater the rarefaction of the existing gas,—the smaller the quantity of the other gas already contained in it (if it be already saturated, no farther

VOL. I.

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