Air resistance

“ Head Resistance—The resistance encountered by a surface moving through the air. 463
Heavier-than-air—A term applied to flying machines whose weight is not counterbalanced or buoyed up by the lifting power of some gas lighter than air; and which weigh more than the volume of air displaced. ”

“ But a smoke particle is moving at a speed measured in inches per second, and is far less likely to hit the wall of the respirator, and be held by its absorbent surface. If we try to make the passages through which air is drawn very narrow, as by sucking in our air through cotton-wool (which will stop most smokes) , we find that we have created an appalling resistance to breathing. ”

“ Dead air space increases the minute-volume. Accordingly, if breathing is accomplished against resistance and through a large volume of dead air space, the volume of air breathed is reduced more in proportion to the actual needs of the body than when breathing against resistance without the additional factor of dead space; this, again, causes the level of carbon dioxide in the blood and tissues to be raised to a higher level than normal, and thus again there is some reserve power wasted. ”

“ In what we have said we have taken no account either of the resistance or of the buoyancy of the atmosphere; in fact, we have supposed the experiments to be made in vacuo, or, if not in vacuo, made by means of a heavy mass, like lead, which will be very little influenced either by the resistance or buoyancy of the air. ”

“ And, when we move our open hand through air at rest, we are still conscious of a resistance, our sense of it being augmented by an extension of the surface moved, as in the act of fanning; while, if the air is in motion, we feel its pressure on the sail of a boat by the "pull" of the sheet we hold in our hand, or on the sails of a windmill by the rotation it imparts, the force of which we can estimate by the effort we must put forth to resist it. Attenuate any kind of air or gas as we may, its resistance can still be made apparent by the like communication of its own motion to solid bodies. ”

“ By some it has been argued that it is better that the foul air should pass off below the level of the person, so that the products of respiration may be immediately drawn below the mouth, and be replaced by descending pure air. But the resistance to be overcome in drawing down the hot air of respiration is so great that there is a considerable waste of power, and the obstacle to the discharge is sometimes sufficient, if the extracting power be at all lessened, to reverse the movement. ”

“ The fact here alluded to is the resistance that bodies experience in moving through the air, which, depending on the quantity of surface merely, must exert a proportionally greater effect on rare substances. ”

“ Composition of air.
It consists essentially of two gases, called oxygen and nitrogen, and also contains a variable quantity of aqueous vapour.
Qualities of air.
In common with matter in every state, the air possesses impenetrability. It can be compressed, but cannot be annihilated. It has weight, inertia, momentum, and elasticity.
In consequence of its weight is its pressure, which acts uniformly on all bodies, and is equal to between 14lbs. and 15lbs. on every square inch of surface at the sea-level.
Early idea of air’s resistance. ”

“ This arises from the fact that bodies moving in air experience a minimum of resistance and occasion a maximum of displacement. Another and very obvious difficulty is traceable to the great disparity in the weight of air as compared with any known solid, and the consequent want of buoying or sustaining power which that disparity involves. ”

“ In order to produce conditions in the open air test similar to those in the cylinder we must devise some method of increasing the resistance of the spark gap in the open air above any possible resistance that could be offered by the carbon film. ”

“ You have probably now the desire to hear from me how much air or ventilation a person wants in a stated time. After you have all the while heard from me that everything is full of air, that air penetrates everywhere, and that it is extremely difficult to prevent its passage, many among you will ask: "What need is there of special contrivances, if the air passes through each brick, through mortar, through wood? Would it not be rather desirable to protect ourselves against this universal aggression of the air?" ”

“ Engine-driving columns of air through a building is not ventilating it. . . . It is wholly misleading to take the registered volumes of air forced into or out of a building at certain points as in any way indicating how often in a given time the whole of the air is changed."—Building News.
Note.—When a volume of air is forced in under pressure a certain portion is deflected and descends, as with the downward system, returning the respired air to be reinhaled, also the products of combustion.'
Air Analysis and Defective Ventilation. ”

“ Do not be fooled by big talk and glib printed matter about high vacuum power, and long air and water columns. What is needed for a good cleaner is air displacement at a sufficiently concentrated point or surface to maintain a high air velocity. ”

“ It is the vitalizing principle in all forms of life. By its chemical union with carbon in the tissues of plants and animals it develops the energy manifested in their movements.
In the free air up to about seven miles high there is no variation in the proportion of oxygen. But variations of marked importance to health and life occur in places where ventilation is restricted, and especially where living creatures exist in closed rooms, and where combustion occurs in confined places. ”

“ Let over-crowding and over-heating be avoided. There should be an abundant supply of pure air. The hours of work should be moderate, with fair intervals for meals. If there is much dust or other foreign matter in the air a suitable respirator should be used, or the offensive particles should be carried off by a current of air produced by a chimney or revolving wheel. Again, mechanical appliances may often take the place of hand-labour, and much may often be accomplished by the application of practical science and chemical knowledge. ”

“ The first rule, therefore, to be laid down in reference to perfect ventilation, prescribes the entire removal of the whole stratum of air tainted in a room by each respiration; for by no less a movement do we conceive it possible to take away the polluted air. This removal must be effected no less than twenty times per minute. Part of the expired air being rarefied by the heat of the lungs will rise, and part—the carbonic-acid gas—will fall. ”

“ There are, of course, great natural causes which affect the air of whole countries, such as the decomposition of great masses of vegetable matter similar to that occurring on the low flat lands along rivers, especially where they overflow their banks, like the Ohio and Mississippi. The best system of ventilation, as applicable to this kind of foul air, is to keep as far out of its reach as possible. ”

“ For the reason that this gas persists longer in calm areas, woods are always to be avoided, where practicable, and also, since all gases, being heavier than air, tend to roll into depressions and valleys, they should be avoided. ”

“ Rigging the air-pump securely round the aperture, exhausting its chamber, and permitting the Martial air to fill it, I was glad to find a pressure equal to that which prevails at a height of 16,000 feet on Earth. Chemical tests showed the presence of oxygen in somewhat greater proportion than in the purest air of terrestrial mountains. It would sustain life, therefore, and without serious injury, if the change from a dense to a light atmosphere were not too suddenly made. ”

“ At a time when the science of ventilation, and the natural laws which govern it, were but imperfectly understood, it was held by many, and still is by some, that a very large volume of air was necessary to dilute the vitiated air in a building to a healthy standard, from 2,000 to 6,000 cubic feet per hour per person being recommended. ”

“ To secure the most perfect diffusion, equable ventilation, and freedom from draught, the fresh air supply should be admitted at a low velocity. The highest authorities fix the maximum speed at from 11⁄2 feet to 2 feet per second. The air should be admitted directly through the walls into the room at a low level and in an upward direction. ”

“ The upper strata of air in the room, charged with the heated products of respiration and combustion, is drawn downwards towards the fire and inhaled by the occupants, who are thus compelled to continuously rebreathe exhausted and impure air. ”

“ Parkes, than whom there is no higher authority, says: "As the ascent of respired air is rapid, on account not only of its temperature, but from the force with which it is propelled upwards, the point of discharge should be above. ”

“ He seems also to think it possible to generate a gas, at a moderate expense, which, by mixing with the atmospheric current, will so far neutralise the inflammable air, as to prevent it firing at the candles of the workmen. ”

“ Now, if you will settle the question of warming and ventilating you shall be honorably discharged. Don't try to show off your science by telling me how carbon, the wicked, poison stuff, is heavy, and we must leave a hole near the floor where it can run out and be coaxed up to the ridgepole after it gets cold, and then make pictures covered with arrow-heads to show how well-educated air ought to go! Talk as many gases as you please to other folks. ”

“ Now, you understand the ground of the impropriety of many of the arrangements among the houses of the poorer classes, by which the air is breathed over and over again, for the want of a supply, by means of proper ventilation, sufficient to produce a good result. You see how bad the air becomes by a single breathing; so that you can easily understand how essential fresh air is to us. ”

“ The wearer uses the same air over and over again, and is able to remain independent of the outer atmosphere for more than an hour. The apparatus is also useful for firemen when they have to pass through thick smoke. ”

“ Incessant movement of the air is a law of Nature. We have only to allow the air in our cities and dwellings to take share in this constant change, and ventilation will go on uninterruptedly without our care."—Parkes.
Why a Natural System of Ventilation is Always in Operation. ”

“ We have now seen that air is a gas, that it exercises pressure, that it possesses weight. We know it can be applied to many useful purposes, and that the air machines and inventions—such as the air-pump and the “Pneumatic Despatch”—are in daily use in our laboratories, our steam engines, our condensed milk manufactories, and in many other industries, and for our social benefit. Compressed air is a powerful motor for boring machinery in tunnels where steam cannot be used, even if water could be supplied, for smoke or fire would suffocate the workers. ”

“ With mechanical ventilation the air is propelled or drawn in at a high velocity ranging from 5 feet to 20 feet per second, destructive of diffusion, and fatal to the effective or comfortable ventilation of a building. As one authority says, "Engine-driving columns of air through a building is not ventilating it." ”

“ Those in which earth and water predominate will be fixed, and will only become volatile by the action of heat; and those which contain most air and fire will be the only real combustibles. The great difficulty here is clearly to conceive how air and fire, both so volatile, can fix and become constituent parts of all bodies. ”

“ There are many different contrivances in use for washing, screening, and purifying the air, the majority of which answer their purpose fairly well, though the evidence would seem to indicate that they are found to be most effective when employed in conjunction with a ' natural ' system of ventilation where the air is not mechanically propelled, but is drawn through by extraction, the air being more thoroughly purified moving in at a low velocity than when forced in under pressure. ”

“ Then there was a society which objected to the use of what they called contaminated air in the air-tubes, by which expression they meant its admixture with oxygen for breathing purposes, which had proved such a boon to the subaqueous inhabitants. Those worthy people contended that the air as it existed in the atmosphere was the proper air for man to breathe, and that its admixture with any foreign ingredient whatsoever was prejudicial, if not to the body, at all events to the mind of those who used it in that state. ”

“ With natural ventilation by diffusion and extraction the evils described cannot occur, as the air is admitted at a level, and in a manner in accordance with the laws of Nature, the hot vitiated air being drawn off at the top of the building, to where it ascends, and not permitted to return, as with downward ventilation, to spread disease and death amongst those compelled to breathe it. ”

“ If the men are willing to take the risk! But we can purify the air to some extent, anyway. I've a man down there with a Burrell gas detector, which is several hundred times more sensitive than any canary, so that we can keep a close watch on the air changes, and there are plenty of tanks of compressed oxygen to be got. I've some here in the car, and a telegram to Pittsburgh will bring us more in a few hours. ”

“ The early recognition during the late war, both by the Sanitary Commission and the government officials, of the important fact that many more men are killed by breathing foul air than are killed by the enemies' bullets, led them to use very active exertions to secure good ventilation in hospitals and camps, and to teach the men themselves the value thereof. The result has been highly satisfactory. The fact that we must make some positive provision for a constant supply of fresh air to every occupied room, and not rely on accidental cracks and openings, is now very generally felt. ”

“ When Priestley commenced his studies, the current belief was, that atmospheric air, freed from accidental impurities, is a simple elementary substance, indestructible and unalterable, as water was supposed to be. When a combustible burned, or when an animal breathed in air, it was supposed that a substance, "phlogiston," the matter of heat and light, passed from the burning or breathing body into it, and destroyed its powers of supporting life and combustion. ”