Porosity

“ In general, the rate at which water will pass through a soil depends on the fineness and approximation of its particles. Water will pass through coarse sand almost as rapidly as through a tube, while a fine clay may be almost impervious. The study of the phenomena of filtration through soil, and the methods of quantitatively estimating them, are therefore closely related to porosity. ”

“ From these and other analogous results we learn that all bodies have a greater or less degree of porosity. The distance at which the particles of fluid bodies are maintained is strikingly proved by the fact, that hydrated salts dissolved in water occupy no more space than that which is equal to the water contained in the crystalline body ”

“ Porosity may thus be regarded as the opposite of vitrification; porous goods being relatively light and [40] soft whilst vitrified ones are dense and hard. For some purposes, porosity is an important characteristic: for example, building bricks which are moderately porous are preferable to those which are vitrified. The manufacture of porous blocks for the construction of light, sound-proof partitions, etc. has increased rapidly of late. They are made by adding sawdust or other combustible material to the clay. The added substances burn out on firing the goods in a kiln. ”

“ The yield of a well will depend, of course, not only on all these factors, but also on the diameter of the bore, its depth into the water-stratum, the size and number of fissures passed through, and, last and most important of all, on the absolute height of its outlet. Large pores, high average porosity, and high temperatures make for strong flows, though in the absence of pressure greater than that due to a column of water equal in height to the distance between the water-stratum and the outlet of the well, they are in themselves of no avail in the production of an artesian flow. ”

“ Basic compounds and fluxes cause a lowering of the melting-point and a shortening of the vitrification range.
The porosity of raw clay is usually of small importance, but the porosity of fired clay or ware is often a serious factor in determining the suitability of certain articles for their intended purposes. In its natural state, clay does not readily absorb much water ”

“ Without undertaking to advance or defend any peculiar geological views of the structure of the earth, or of the depositions or formations that compose its surface, it may be said, that very often the first four feet of subsoil is composed of strata, or layers of earth of varying porosity. ”

“ Since the freedom of movement of ground-water is notably influenced by the porosity of the rock, and since the rock is, on the average, most porous and the pores largest near the surface, the movement of ground-water is, on the average, greatest near the surface, and least at its lower limit. In general the decrease of movement is much more rapid than the decrease in the size of the pores. ”

“ A superficial soil of this kind, from twenty inches to three feet in depth, can scarcely suffer from porosity, and that it does not, is evident from the heavy crops of grain and grass it yields, and the luxuriant growth of fruit trees on the improved spots, as well as the immense burthen of forest trees and vegetation it bears in its native condition. I believe that the under stratum of coarse gravel which must cause this porosity, if it exists, has no greater effect upon the superficial soil than would be produced on any earth by a thorough system of under-draining. ”

“ The porosity of materials has been obviated by injecting them with gas-refuse, by immersing or washing them in solutions of soap and alum successively, by plunging them into a solution of silicate of potash, and by painting them with gas-tar. Mortars are made impervious by mixing them with cement. ”

“ When heated moderately, clay forms a porous material and, unless the heating is excessive, it will absorb about one-eighth of its weight of water. Further heating at a higher temperature reduces its porosity—the more easily fused material filling some of the pores—until a stage is reached when the material is completely vitrified and is no longer porous. ”

“ Favorable conditions for trapping the oil may be furnished by impervious clay "gouges" along fault planes, or by dikes of igneous rock. Favorable conditions may also be merely differences in porosity of beds in irregular zones, determined by differences either in original deposition or in later cementation. ”

“ The precipitation and dissolution processes changes the porosity, which in turn changes the transport properties. It is the act of maintaining chemical equilibrium that affects the synergism of the different degradation mechanisms. ”

“ The rate of flow of water through an underground sandstone depends upon a number of conditions, the most important being the size of the pores or spaces between the component grains, the porosity or water-holding capacity of the sandstone, the temperature of the water, and the pressure acting on it. ”

“ Porous ware, in which round and square porous cells, plates, &c., are extensively made, and have been used by some of the first telegraphic engineers, philosophical instrument makers, &c., of the day, and have given much satisfaction, securing, as they do, the greatest amount of porosity, together with a degree of hardness and fineness of texture which render them insusceptible of disintegration. ”

“ Further questions to be considered in the exploration of an area are the content of organic matter in the sediments which may have served as a source of oil, the presence of impervious cap-rocks or of variations in porosity sufficient to retain the oil, the thickness of sediments and the extent to which they have undergone differential stresses, the amount of erosion and the possibilities that oil, if formed, has escaped from the eroded edges of porous strata, and, where carbonaceous beds are present, their degree of carbonization, and many other similar matters. ”

“ Porosity.—All matter has little hollows or spaces between the molecules. You know what this is in the case of a sponge, or pumice stone. Certain metals have the pores so small that it is difficult to see them except with a very powerful glass. Under great pressure water can be forced through the pores of metals, as has been done inp. ”

“ As the is leached, the porosity increases. Let the value of porosity after leaching be , and the diffusivity be . Unfortunately, the ratio is not simply because as calcium hydroxide is leached from the paste the ratio does not retrace eqn. 27. Rather, the ratio is greater than , as demonstrated by the NIST microstructural model.
The NIST cement microstructural model [14] was used to determine the relation for upon leaching. Results for a paste are shown in Figure 2. The formation factor decreases with decreasing porosity due to hydration, denoted by circles. ”

“ Effect of pressure on water capacity; Coefficient of evaporation; Determination of capillary attraction; Inverse capillarity; Determination of coefficient of evaporation; Wolff’s method; Water given off in a water-free atmosphere; Porosity of soil for gases; Determination of permeability in the field.
Movement of Water Through Soils: Lysimetry, pp. 151–170.—Porosity in relation to water movement; Methods of water movement; Capillary movement of water; Causes of water movement; Surface tension of fertilizers; Methods of estimating surface tension; Preparation of soil extracts ”

“ Seeping through the mantle of waste, ground water soaks into the pores and crevices of the underlying rock. All rocks of the upper crust of the earth are more or less porous, and all drink in water. Impervious rocks, such as granite, clay, and shale, have pores so minute that the water which they take in is held fast within them by [40] capillary attraction, and none drains through. Pervious rocks, on the other hand, such as many sandstones, have pore spaces so large that water filters through them more or less freely. ”

“ Such induration may perhaps be accounted for by supposing the water, which penetrates the minutest pores of rocks, to deposit, on evaporation, carbonate of lime, iron, silex, and other minerals previously held in solution, and thereby to fill up the pores partially. These particles, on crystallising, would not only be themselves deprived of freedom of motion, but would also bind together other portions of the rock which before were loosely aggregated. On the same principle wet sand and mud become as hard as stone when frozen ”

“ THE ZONE OF SOLUTION. Near the surface, where the circulation of ground water is most active, it oxidizes, corrodes, and dissolves the rocks through which it passes. It leaches soils and subsoils of their lime and other soluble minerals upon which plants depend for their food. It takes away the soluble cements of rocks; it widens fissures and joints and opens winding passages along the bedding planes; it may even remove whole beds of soluble rocks, such as rock salt, limestone, or gypsum. The work of ground water in producing landslides has already been noticed. ”

“ In what manner silex and carbonate of lime may become widely diffused in small quantities through the waters which permeate the earth’s crust will be spoken of presently, when the petrifaction of fossil bodies is considered; but I may remark here that such waters are always passing in the case of thermal springs from hotter to colder parts of the interior of the earth; and, as often as the temperature of the solvent is lowered, mineral matter has a tendency to separate from it and solidify. Thus a stony cement is often supplied to sand, pebbles, or any fragmentary mixture. ”

“ Such rocks are called strata. They may be of mechanical origin such as clay or mud which hardens to shale; sand, which consolidates into sandstone; and gravel, which when cemented becomes conglomerate. They may be of organic origin such as limestone, most of which is formed by the accumulation of calcareous shells; flint and chert, which are accumulations of siliceous shells; or coal, which is formed by the accumulation of partly decayed organic matter. Or, finally, they may be formed by chemical precipitation, as beds of salt, gypsum, bog iron ore, etc. ”

“ Here it accumulates. Most of it is clay, but there is some sand, and the whole is tinged red by the oxide of iron, which, by exposure to the air and water has been raised, if it were not previously in that condition, to the state of the hydrated peroxide. If we could measure the cubical contents of such a deposit, and also by analysis determine accurately the composition of the rock from which it was derived, we might obtain some interesting results as to the amount of denudation of the district in recent times. ”

“ The main requisites for a productive oil or gas field are a porous reservoir and an impervious cover. Thus, while the mineral ma be formed in a stratum other than that in which it is found, though in many cases it is indigenous to it, for the formation of a natural reservoir of the fluid (whether liquid or gas) it is necessary that there should be a suitable porous rock to contain it. ”

“ This diagram shows plainly that there is no direct relation between the total pore-space in a soil and the facility of water-penetration. The highest pore-space, in the fine-grained alluvial loam, allows more rapid percolation than the heavy clay or adobe soil, but is greatly exceeded by the coarser sandy soil. In all it is very apparent that the downward movement slows down as the water descends, doubtless because the great friction in a longer column gradually diminishes the effect of hydrostatic pressure. ”

“ Sediment is generally deposited as a soft mud, but in nearly all the older formations it has become solidified. When rocks are deposited from a chemical solution, they take at once the solid form. Such is the case with rock-salt and with limestone, when the material has been held in solution. Solidification takes place in nearly the same way when water which holds carbonate of lime or oxide of iron in solution filters through beds of sand or gravel. The substance held in solution is deposited in the interstices till they become filled, and the whole is changed to solid rock. ”

“ The laterite beds are porous, in fact they are traversed by innumerable tubules which are often lined with deposits of iron oxide and aluminous minerals. We may be certain that, as in all soils during dry weather, there is an ascent of water by capillary action towards the surface, where it is gradually dissipated by evaporation. The soil water brings with it mineral matter in solution, which is deposited in the upper part of the beds. If the alumina be at one time in a soluble condition it will be drawn upwards and concentrated near the surface. ”

“ The material forming this deposit is an emulsion of water, gas, bitumen and mineral matter, the latter consisting largely of fine sand and a lesser amount of clay. It is in constant motion, owing to the evolution of gas, and for this reason whenever a hole is dug in the surface, whether deep or shallow, it rapidly fills up, and the surface resumes its original level after a short time. While sufficiently soft to accommodate itself to any change of level and to slow movement, it can be readily flaked out with picks, in large conchoidal masses weighing from 50 to 75 pounds. ”

“ Time, as I have explained in Chapters V, VI, and VII, has multiplied the effects of condensation by pressure and cementation, and the modification produced by heat, fracture, contortion, upheaval, and denudation. The organic remains also have sometimes been obliterated entirely, or the mineral matter of which they were composed has been removed and replaced by other substances.
Why newer Groups should be studied first.—We likewise observe that the older the rocks the more widely do their organic remains depart from the types of the living creation. ”