Fluid accumulation

“ Osmosis takes place when two fluids of different osmotic pressure are separated by animal membrane. Difference in osmotic pressure is due to differences in molecular concentration, the greater the number of molecules the greater is the pressure, and the greater rapidity of flow is from the fluid of less pressure to the fluid of greater pressure. The molecular concentration of tissue and blood fluid is constantly being equalized by the process of osmosis. ”

“ The explanation, of course, is simple. The brine is of greater specific gravity than the pure water; the pressure of the heavier fluid forces the lighter up in the tube. This action continues until, as you will see by this experiment, in the gradual diffusion of brine and pure water the salt is disseminated equally throughout the vessels, and the specific gravity of the mixed liquid becomes the same throughout, when the flow will cease. However, in the earth, where supplies are inexhaustible, the fountain flows unceasingly. ”

“ It is found that, under ordinary circumstances, evaporation is confined to the surface of the heated liquid, and is therefore slower or quicker, in proportion to the extension of that surface. Hence has arisen the adoption of wide, shallow vessels for containing fluids during their exposure to heat for this purpose. Evaporation proceeds most rapidly when a current of air (especially hot and dry air) is made to pass over the surface of the fluid; as, in this ease, the vapour is prevented from resting upon the surface, and impeding the process by its pressure. ”

“ We will now consider the stability of a fluid enclosed in a rigid envelop which is non-conducting to heat and impermeable to all the components of the fluid. The fluid is supposed initially homogeneous in the sense in which we have before used the word, i.e., uniform in every respect throughout its whole extent. Let be the ultimate components of the fluid; we may then consider every body which can be formed out of the fluid to be composed of , and that in only one way. Let denote the quantities of these substances in any such body, and let , denote its energy, entropy, and volume. ”

“ But, further, in fluids such as water, air, steam, &c., to which the present division of the article relates, the tangential stresses that are called into action between contiguous portions during distortion or change of figure are always small compared with the weight, inertia, pressure, &c., which produce the visible motions it is the object of hydraulics to estimate. On the other hand, while a fluid passes easily from one form to another, it opposes considerable resistance to change of volume. ”

“ In the latter case these obstacles are avoided, and the impetus of the vapour pouring forth from a contracted orifice (or pipe) , not only readily overcomes the pressure of the atmosphere, but offers less surface for its cooling action, until it has passed much beyond the points at which it can exert any influence on the fluid from which it has escaped. In this way the chemical action of the atmosphere on the liquid operated on is also considerably lessened. ”

“ There is also an intimate connection with the pressure under which a fluid is boiled, and its temperature of ebullition. Liquids boiled in the open air are subjected to the atmospheric pressure, which is well known to vary at different times and places; and the boiling-point of the liquid exhibits corresponding changes. When the pressure is increased on the surface of any fluid, the temperature of ebullition rises; and with a decrease of pressure, the boiling goes on at a lower degree of heat. ”

“ A less fluid type will become markedly scoriaceous, where the vapours endeavour to escape from it; the rugged crust formed on its upper cooling surface will be broken up by the continued movement of the more liquid mass below, and the blocks thus formed may become rolled over the advancing front of the flow and entombed in the portion that has not yet consolidated. ”

“ We hardly know any Fluid in all Nature, except Fire, whose constituent Parts are so exceeding subtle and small as those of Water are. They'll pass Pores and Interstices, that neither Air nor any other Fluid will. This enables them to enter the finest Tubes and Vessels of Plants, and to introduce the Terrestrial Matter, conveying it to all Parts of them; whilst each, by means of Organs 'tis endowed with for the Purpose, intercepts and assumes into it self such Particles as are suitable to its own Nature, letting the rest pass on through the common Ducts. ”

“ When not entirely transparent they frequently contain inclusions of black asphaltum or other hydrocarbons and also contain hollow cavities which are filled with fluid, sometimes salt water and sometimes liquid carbonic acid gas. In these are moving bubbles and occasionally a heavy hydrocarbon; that is, a bubble will ascend and the hydrocarbon will sink; or else the bubble will rise and take with it a small speck of hydrocarbon, and another will sink. ”

“ When such a receiver is connected with an air-pump in action, evaporation proceeds with increased rapidity, and intense cold is produced. It appears, from the experiments of Dr Ure, that “if the bottom of a pan, and the portion of the sides immersed in a hot fluid medium (solution of chloride of calcium, for example) , be corrugated, so as to contain a double expanse of metallic surface, that pan will evaporate exactly double the quantity of water, in a given time, which a like pan, with smooth bottom and sides, will do, immersed equally deep in the same bath. ”

“ A solid body—a metallic bar for example—alternately heated and cooled increases and diminishes in length, and can move bodies fastened to its ends. A liquid alternately heated and cooled increases and diminishes in volume, and can overcome obstacles of greater or less size, opposed to its dilatation. An aeriform fluid is susceptible of considerable change of volume by variations of temperature. If it is enclosed in an expansible space, such as a cylinder provided with a piston, it will produce movements of great extent. ”

“ The Science of Hydrostatics depends upon the Fundamental Principle that fluids press equally in all directions. This principle necessarily results from the conception of a Fluid, as a body of which the parts are perfectly moveable in all directions. For since the Fluid is a body, it can transmit pressure; and the transmitted pressure is equal to the original pressure, in virtue of the Axiom that Reaction is equal to Action. That the Fundamental Principle is not derived from experience, is plain both from its evidence and from its history. ”

“ In general the space will remain filled with fluid if the pressure at every point remains positive. There will be a break of continuity, if at any point the pressure becomes negative, indicating that the stress at that point is tensile. In the case of ordinary water this statement requires modification. Water contains a variable amount of air in solution, often about one-twentieth of its volume. This air is disengaged and breaks the continuity of the liquid, if the pressure falls below a point corresponding to its tension. ”

“ To this if we add a Pression of the several Parts of the Fluid every way, and consider withal, that this Uniform Attraction of the Parts to one another must be variously changed by the different Attraction of Heterogeneous Bodies mixt with them, we have the great Principles of all Fluids, upon which their several Phænomena do depend.
And hence it follows, that whatsoever Power is sufficient to make a Change in this Attraction, or Cohæsion of the Parts, makes an Alteration of the Nature of the Fluid; that is, as the Chymists express it, puts it into a Fermentation. ”

“ Spirit of wine flies off in vapour much sooner than water; so that if you had a mixture of the two, by applying a gentle heat you might drive off almost all the spirit, while the greater part of the water would remain. Water, again, is more evaporable than oil. Some solid substances are much disposed to evaporate: thus, smelling salts may by a little heat be entirely driven away in the air. But in general, solids are more fixed than fluids; and, therefore, when a solid is dissolved in a fluid, it may commonly be recovered again by evaporation. ”

“ The pores of all bodies are supposed 117to be full of this subtile fluid; and when its equilibrium is not disturbed, that is, when there is neither more nor less of it in a body than its natural share, or than it is capable of retaining by its own attraction, the fluid does not manifest itself to our senses. The action of the rubber upon an electric disturbs this equilibrium, occasioning a redundancy of the fluid in one place, and a deficiency of it in another. This equilibrium being forcibly disturbed, the mutual repulsion of the particles of the fluid is necessarily exerted to restore it. ”

“ By the aid of pressure and of low temperatures, the force of cohesion may be so far increased in many gases that they are readily converted into liquids, and we know now that with sufficient pressure and cold they may all be liquified. On the other hand, heat, which increases the vis viva of the molecules, converts liquids, such as water, alcohol and ether or gas into the aëriform state in which they obey all the laws of gases. The aëriform state of liquids is known by the name of vapor, while gases are bodies which, under ordinary temperature and pressure, remain in the aëriform state. ”

“ Whenever the elasticity of the vapour, corresponding to the temperature of the water, is greater than the atmospheric pressure, the evaporation will take place not only from its surface, but from every point in its interior; the liquid particles throughout the mass assuming the gaseous form, as rapidly as they are actuated by the caloric, which subverts the hydrostatic equilibrium among them, to constitute the phenomena of ebullition. ”

“ However clear and pellucid the liquid may have been, when first prepared, however carefully it may have been freed from even the finest visible impurities, by straining and filtration, it will not remain clear. After a time it will become cloudy and turbid; little bubbles will be seen rising to the surface, and their abundance will increase until the liquid hisses as if it were simmering on the fire. By degrees, some of the solid particles which produce the turbidity of the liquid collect at its surface into a scum, which is blown up by the emerging air-bubbles into a thick, foamy froth. ”

“ Thus, when a gas is absorbed by water, much heat is evolved, and we may suppose the result to be due in part to chemical combination, and in part to the condensation of the gas into a liquid, by which means its latent heat is rendered sensible. On the other hand, when a liquid unites with a solid, or when two solids unite with one another, and the product is a liquid, we have very often the absorption of heat, the heat rendered latent by the dissolution of the solid being more than that generated by combination. ”

“ As we find the liquid water in nature it is more or less impregnated with vegetable, gaseous, and saline matter, which often impairs its fitness for mechanical purposes. These admixtures are derived from the rocks and ground over or through which the water flows. The incrustations which form in boilers are caused by the precipitation of the impurities in consequence of the concentration of water in the boiler. ”

“ If the vessel was so large that in different parts of it the temperature and pressure were different, the diffusion would, indeed, still be perfect, because at all ordinary temperatures and pressures hydrogen and carbonic acid gas remain gaseous. But if the vapour introduced is of such a nature that at moderate temperatures and pressures it condenses, wholly or in part, or liquefies, the diffusion will not take place with the same uniformity. We need not go further for illustration than to the case of our own atmosphere as it actually exists. ”

“ If we mix them in a vessel and apply a match, there is instantly a powerful explosion, heat is generated and there is formed—water. The two strange, invisible gases have combined and formed the well-known liquid. Whenever a substance which contains hydrogen, like wood, paper, starch, sugar, &c., burns, it forms water with oxygen of the air. In fact, these two gases are always ready, on the slightest provocation to unite. Rain, or melted snow, approaches nearest to chemically pure water, but all wells, springs, rivers and seas contain dissolved substances, in greater or less degree. ”

“ This is not boiling, as may be proved by trying the temperature with the finger. What, then, is it?
It is the yielding back of the atmospheric gases which the water has dissolved or condensed within itself. These bubbles have been collected and by analysis proved to consist of oxygen, nitrogen, and carbonic acid, obtained from the air; but in the water they exist by no means in the same proportions as originally in the air, nor in constant proportions in different samples of water. ”

“ Quite often the work has been delayed and the tunnel partly or wholly flooded. Now, you know the theory of the bends. It is that air—mostly the nitrogen in the air—is absorbed by the blood under the pressure. In coming out of the 'air' if the nitrogen is not all eliminated, it stays in the blood and, as the pressure is reduced, it expands. It is just as if you take a bottle of charged water and pull the cork suddenly. The gas rises in big bubbles. Cork it again and the gas bubbles cease to rise and finally disappear. ”

“ In density there is a great difference; water, which is the type of liquids, is 770 times as heavy as air, the type of gaseous bodies, while under the pressure of one atmosphere. A spiral spring only shows elasticity when it is compressed; it loses its tension when it has returned to its primitive condition. A gas has no original volume; it is always elastic, or in other words, it is always striving to attain a greater volume; this tendency to indefinite expansion is the chief property by which gases are distinguished from liquids. ”