Hydrostatics

“ The difficulty of holding fast this Idea of Fluidity so as to trace its consequences with infallible strictness of demonstration, may be judged of from the circumstance that, even at the present day, men of great talents, not unfamiliar with the subject, sometimes admit into their reasonings an oversight or fallacy with regard to this very point. The importance of the Idea when clearly apprehended and securely held, may be judged of from this, that the whole science of Hydrostatics in its most modern form is only the development of the Idea. ”

“ The laws of motion of visible and tangible, or molar, matter had been worked out to a great degree of refinement and embodied in the branches of science known as Mechanics, Hydrostatics, and Pneumatics. These laws had been shown to hold good, so far as they could be checked by observation and experiment, throughout the universe, on the assumption that all such masses of matter possessed inertia and were susceptible of acquiring motion, in two ways, firstly by impact, or impulse from without; ”

“ The theorems of hydrostatics are thus true for all stationary fluids, however viscous they may be; it is only when we come to hydrodynamics, the science of the motion of a fluid, that viscosity will make itself felt and modify the theory; unless we begin by postulating the perfect fluid, devoid of viscosity, so that the principle of the normality of fluid pressure is taken to hold when the fluid is in movement.
5. The Measurement of Fluid Pressure.—The pressure at any point of a plane in the interior of a fluid is the intensity of the normal thrust estimated per unit area of the plane. ”

“ If a fluid be composed of particles mutually flying each other, and the density be as the compression, the centrifugal forces of the particles will be reciprocally proportional to the distances of their centres. And vice versa, particles flying each other with forces that are reciprocally proportional to the distances of their centres, compose an elastic fluid, whose density is as the compression. ”

“ 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. ”

“ These bubbles are the two elements of water, hydrogen on the one hand, and oxygen of the other. The gases emerge through the tubes g and g1. If we wait until the upper part of the vessels and the tubes have been filled with it, we can inflame hydrogen at one side; it burns with a blue flame. If I bring a glimmering spill near the mouth of the other tube, it bursts into flame, just as happens with oxygen gas, in which the processes of combustion are far more intense than in atmospheric air, where the oxygen mixed with nitrogen is only one-fifth of the whole volume. ”

“ The better hydrogen becomes known, therefore, the more interesting and important to us it is found beyond all other elements, oxygen scarce excepted. To all the vital and delightful uses of water, as we have seen, it adds also those of light and heat. For, although scarcely luminous in itself, hydrogen is a principal source of the heat which makes other substances luminous, and is thus a chief condition of illumination. Terrestrial flame is generally hydrogen gas in the act of combustion, colored and made brilliant with white-hot carbon also oxidizing. ”

“ I have repeated this experiment often. The elements of the water dissociate by the heat, and instantaneously recombine in cooling, causing the detonation."
The degree of dissociation, as of evaporation, depends on the pressure: under four atmospheres (60 lbs.) , the heat required for dissociation is 1,870° . But the question arises, If the vapor dissociates at these temperatures, why do not the gases instantaneously combine and detonate? The reason is plain: in the boiler the atoms at once become mixed with a volume of steam sufficient to render them inexplosive. ”

“ If a tolerably large jar containing hydrogen is now placed over the porous cell, bubbles of gas make their escape at the end of the tube, because the hydrogen diffuses itself more rapidly into the porous cell than the air which it already contains passes out. When the jar is removed, the reverse occurs, hydrogen diffuses out of the porous cell, and the blue liquid rises in the tube.
This diffusive force prevents the accumulation of the various noxious gases on the earth, and spreads them rapidly through the great bulk of the atmosphere surrounding the globe. ”

“ There is a force that we may call polar force, which is constantly tending to push the molecules of water into an arrangement such as we see when crystallization takes place—as it always does in the act of freezing. These polar forces cannot act so long as the energy in the form of heat is sufficient to hold the water in the fluid state. But the moment this energy, which tends to hold it in the fluid state, falls below that which tends to rearrange it into the crystalline form, it is overcome by the superior power of the latter force, and we have the phenomenon of solidified water. ”

“ Gravity, as hydrogen is taken as the standard for Atomic Weight. The uses of water and the very important part it plays in the arrangements of nature as a mechanical agent, geology can attest, and meteorology confirm. It composes the greater portions of animals and plants; without water the world would be a desert—a dead planet.
Fig. 341.—Blowing bubbles with hydrogen gas.
We sometimes speak of “pure” spring water, but such a fluid absolutely pure can scarcely be obtained; and though we can filter water there will always remain some foreign substance or substances in solution. ”

“ There will, however, be somewhere an elevation at which the heat evolved by the joint compression of the elementary and combined gases will be just sufficient to dissociate the latter, and here will be the meeting surface of the combined and the uncombined constituents of water. There will be a sphere containing combined oxygen and hydrogen surrounded by an atmospheric envelope containing large quantities of aqueous vapor, and the temperature at this limiting surface will be equal to that of the oxyhydrogen flame under a corresponding pressure. ”

“ He has seen isolated cloudlets form and grow spontaneously without any perceptible connection with the chromosphere or other masses of hydrogen, just as in our own atmosphere clouds form from aqueous vapor, already present in the air, but invisible until some local cooling or change of pressure causes its condensation. Granting the correctness of the observation, these prominences are, therefore, formed by some local heating or other luminous excitement of hydrogen already present, and not by any transportation and aggregation of materials from a distance. ”

“ Let us for a moment consider this fluid we call water, especially sea water. Chemically speaking, pure water is one of the rarest things—that is, water absolutely free from all foreign matter, divested of everything save hydrogen and oxygen in the combining proportions, by weight one part of hydrogen to eight of oxygen; by volume, two of hydrogen to one of oxygen, we have pure water—an oxide of hydrogen. But absolutely pure water must be prepared in a vacuum, and it must never have contact with air of any kind. ”

“ Hydrogen is the lightest of all the gases, and unquestionably took its place on the outer limits of the atmosphere. There it was brought into contact with oxygen by the commotion of the elements, and converted into steam as fast as its lowering temperature allowed of the combination. As we might expect from the respective positions of the gases, all the hydrogen which fell to the portion of the earth in the making up of its constituents was transformed into water-vapor. Hydrogen is found in no other combination that cannot be traced directly or indirectly to the decomposition of water. ”

“ Perfectly pure water is without taste: even the pleasant character of freshly-drawn spring-water is due to the admixture of atmospheric air and carbonic acid. The manner in which water absorbs air is evidently due to a peculiar physical attractive force, the value of which we do not at present clearly perceive or correctly estimate. It is chemically composed of two volumes of hydrogen gas—the lightest body known, and at the same time a highly inflammable one—united with one volume of oxygen, which excites combustion, and continues that action,—producing heat and light,—with great energy. ”

“ The paraffin oil used in these experiments had, at a temperature of 12°·5 centigrade, a specific gravity ·840 and a surface-tension about ·39 of that of water. Since only a small increase of height was required with this liquid to make a smooth sphere give [pg 102] the same splash as a rough one, this liquid was found much more convenient than water in investigating the transition.
When water is made more viscid by the gradual addition of glycerine, [H] the surface-tension and the specific gravity are but little altered though the viscosity is steadily and sensibly increased. ”

“ The ionization of water, slight as it is, yields hydrogen-ion and hydroxide-ion, the ions characteristic of acids and of bases, and water is placed among the weakest of the acids (see table, p. 104) as well as among the weakest of the bases (table, p. 106) . We shall return to these relations, presently, and shall find that the apparent weakness of water, as a base and as an acid, is seemingly very largely due to the fact that water represents only an extremely dilute solution (see p. 66) of the real hydroxide, HOH, or hydrol, and consists very largely of a compound (H2O) 2. ”

“ I hold that the sympathetic neutral flow which exists in this remote region is the latent power that, under the disintegration of water, is liberated; showing immense volume and infinite pressure. The same condition of latent power exists in metallic masses and, paradoxical as it may seem, exerts its force, under the proper exciter, only in a negative attractive way, while in water in a positive one. In minerals under liberation this latent power seeks its medium of tenuous equilibrium, leaving behind an impalpable dust, that represents molecular dissociation. ”

“ Heat promotes Fluidity very much by diminishing the Tenacity of Bodies. It makes many Bodies fluid which are not fluid in cold, and increases the Fluidity of tenacious Liquids, as of Oil, Balsam, and Honey, and thereby decreases their Resistance. But it decreases not the Resistance of Water considerably, as it would do if any considerable part of the Resistance of Water arose from the Attrition or Tenacity of its Parts. And therefore the Resistance of Water arises [Pg 368] principally and almost entirely from the Vis inertiæ of its Matter ”

“ The experiments were renewed in 1899, with the advantage of more knowledge concerning reductions of temperature brought about by reduction of pressure. A slight leak of air in the apparatus was observed, which was frozen into an air snow when it met the cold vapor of hydrogen coming off, and this leak at a particular point of pressure caused a sudden solidification of the liquid hydrogen into a mass like frozen foam. An apparatus was then arranged that could be overturned, so' that if any of the hydrogen was still liquid it would run out. ”

“ If the instrument be filled with helium at atmospheric pressure and a charcoal bulb attached to it be cooled in liquid air, the vanes remain motionless even when exposed to the concentrated beam of an electric arc lamp; but if liquid hydrogen be substituted for the liquid air rapid rotation at once sets in. When a similar radiometer was filled with hydrogen and the attached charcoal bulb was cooled in liquid air rotation took place, because sufficient of the gas was absorbed to permit motion. ”

“ Water recently boiled will absorb, if cold, about twice its bulk of chlorine gas, acquiring its color and characteristic properties. The moist gas, exposed to a cold of 32 deg., yields beautiful yellow crystals, which are a definite compound of one equivalent of chlorine and ten of water. If these crystals are hermetically sealed up in a glass tube, they will, on melting, exert such a pressure as to liquefy a portion of the gas, which is distinctly seen as a yellow fluid, not miscible with the water which is present. ”

“ The solution of mineral matter by ground water, as well as the other chemical changes it effects, is greatly augmented by the impurities, especially carbonic and other organic gases, dissolved by the water from the atmosphere and the soil. The commonest chemical changes effected by the joint action of water and air, oxidation and carbonation, have been referred to in Chapter II. Hydration is more exclusively the work of water, and is one of the commonest processes of rock change, and often of rock disintegration. ”

“ We know that, floating around us, these volatilized bodies exist in some material form, and numerous experiments in chemistry are calculated to convince us, that the most attenuated air is capable, with a slight change of circumstances, of being converted into the condition of solid masses. Hydrogen gas, the lightest, the most ethereal of the chemical elements, dissolves iron and zinc, arsenic, sulphur, and carbon; and from the transparent combinations thus formed, we can with facility separate those ponderous bodies. Such substances must exist in our own atmosphere ”