Dry air

“ As our dry air is surrounded on both sides by moist air, it is evident that we must more or less partake of both heat and cold; but it moreover accounts for the happy circumstance that we have much rain ”

“ Such air is very dry and takes moisture in an excessive degree from the moist linings of the human respiratory tracts and thus irritates and fatigues the people exposed to the dry air, becoming a serious menace to comfort and even to health. ”

“ The qualities hitherto sought in a hygrometer, or instrument to discover the degrees of moisture and dryness [136] in the air, seem to have been, an aptitude to receive humidity readily from a moist air, and to part with it is as readily to a dry air. ”

“ The reason for this is that if the air is dry the heat passes through it and warms it but little. Moisture stops the radiated heat that would be lost, absorbs it, and holds it at the place where it is needed. It has precisely the same effect as a soft wool blanket wrapped about the body of each person. The dry air permits such a rapid evaporation from the human body that one may actually feel colder with a dry air heated to 75° than in a moist air at 66° or 68°. Water is cheaper than coal, and in this matter much more healthful. ”

“ The wick carries water to the bulb just as a lamp wick carries oil to the flame. The psychrometer is seen inside the shelter on the right in Fig. 2.
Fig. 8.
The air always has more or less moisture in it. Even the hot, dry air of deserts contains some moisture. This moisture is either invisible or visible. When invisible it is known as water vapor, and is a gas. When visible, it appears as clouds and fog,29 or in the liquid or solid form of rain, snow, and hail. The amount of moisture in the air, or the humidity of the air, varies according to the temperature and other conditions. ”

“ In calm weather vapour accumulates in the stratum of air immediately above the evaporating surface, and retards the formation of more; whereas a strong wind accelerates the process by carrying off the vapour as soon as it rises, and making way for a succeeding portion of dry air. ”

“ The fresh air thus admitted at the bottom of the tube being cold and dry, will be suited to take up the heat and moisture within, because the water within the tube being in a state of dispersion as rain, presents to the air many points, or a very extended surface, and also because it is of a higher temperature than the air; and, besides, cold dry air is continually renewed, and a source of warmth is furnished by the latent caloric to the steam, as fast as it is evolved. ”

“ If the air is saturated with moisture, even though the temperature is not above 70 or 75 degrees, the perspiration is not readily evaporated from the surface of the body. If the air is dry the temperature may be much higher and we be much more comfortable, because evaporation goes on rapidly, which keeps the body not only dry, but cool. ”

“ We ventilate to remove smoke and ordinary dust; these are easily seen; and we use ventilation to procure dryness. Moisture rises constantly from the skin, and, if an inhabited apartment is not ventilated, that moisture accumulates. By opening the windows we cause floors to dry sooner, and we remove moisture from all the apartments, and that moisture has generally organic matter with it. If we ventilate with very moist air, we shall dry nothing; if we have very dry air, we may dry too thoroughly. ”

“ It is an element of much practical interest, because it is one of the main factors in determining the drying power of the air, the other important one being wind. The air feels dry when evaporation proceeds rapidly from our skin, either on account of low relative humidity, brisk air movement, or both. People are hardly conscious of high relative humidity except when, in hot weather, it retards the evaporation of perspiration, and the latter collects in liquid form on the skin. ”

“ The rapid evaporation of the ice filled the air so full of water vapor that evaporation of sweat could not take place and the persons in the room were much worse off than if they had contented themselves with merely keeping the warm and comparatively dry air of the room in rapid motion. ”

“ In moist weather the cloud hangs long and lazily in the air; in dry weather it is rapidly licked up. What has become of it? It has been reconverted into true invisible vapor. The drier the air, and the hotter the air, the greater is the amount of cloud which can be thus dissolved in it. ”

“ Every housewife that but once in her life hung up clothes to dry, knows full well that air absorbs moisture when passing over, or through, wet objects. If she wishes to dry her clothes very quickly, she will hang them up where there is much wind. And she is perfectly right in maintaining that the wind dries clothes better than the quiet sunshine. ”

“ CHANGING ATMOSPHERE.—If the air is full of moisture, as it may be at some places, while comparatively dry at other points, the reflection throughout the moist area is much greater than in the dry places, hence evaporation will take place and whenever a liquid vaporizes it means heat. ”

“ Air in order to be comfortable should contain some moisture. Out-of-doors air is, under usual conditions, from 30 to 70 per cent. saturated and such a degree of saturation is, in accordance with investigations, more sanitary than either extremely dry or extremely damp air. When air is saturated with moisture, water is deposited on all bodies which conduct heat readily and have a lower temperature than the air. ”

“ So concreted humid things attract when a little resolved into air (the effluvia in the intermediate space tending to produce unity) ; for water has on wet bodies, or on bodies wet with abundant moisture on the top of water, the force of an effluvium. Clear air is a convenient medium for an electrical effluvium excited from concreted humour. Wet bodies projecting above the surface of water (if they are near) run together so that they may unite; for the surface of the water is raised around wet substances. But a dry thing is not impelled to a wet one, nor a wet to a dry, but seems to run away. ”

“ They are so hot and dry that green leaves and grass are rendered as dry as powder in a few minutes. These winds are probably caused by the fact that at this season of the year, when the prevailing wind is southwesterly, the air becomes heated to a great height, and are the resulting effect of certain combinations of air currents in the higher regions of the atmosphere that force the already heated air toward the earth. ”

“ Therefore, under sunshine, the dry soil becomes warmer than the wet and, whether or not it has a greater quantity of heat to give off at night, it has a higher temperature and therefore radiates more freely to the air above. ”

“ Now, besides the mutual Affinity that Water has to almost all Kinds of Air, and to Floguiston; added to its Power of Absorption; and as the sea, particularly in Summer, also rivers and damp meadows are generally cooler than the Lands and Countries bordering on them; Currents of damp cool Air press forwards to supply the Defect or Vacancy caused by Heat, Rarefaction and Elevation of dry warm Air, which is necessarily, and almost constantly rising into the Atmosphere, from heated Lands, Plains, and gentle Eminences long shone on by the Sun. ”

“ It is absorbed into the dry atmosphere. But when the day is “damp” we find that the air has nearly as much moisture as it can carry, and the steam is condensed, a portion falling in tiny drops like rain. This is proved every day in cold weather when ice is found in the windows—the cold air has condensed and frozen the water breathed out from our lungs, and snow has been known to fall in a ball-room when a cold current of air was admitted. ”

“ Again, the air should be pure, and free from redundant moisture. In the warm mornings of July and August, the air is loaded with moisture and impurities, and the perspirable matter is not removed from the system as it is when the air is pure and dry. ”

“ When air, at a given temperature, has only forty per cent of the moisture it requires for saturation, it is said to be dry. In a hot summer day, the air will hold far more moisture than in cool days. In summer, out-door air rarely holds less than half its volume of water. In 1838, at Cambridge, Massachusetts, and New-Haven, Connecticut, at seventy degrees, Fahrenheit, the air held eighty per cent of moisture. ”

“ Whenever water is left freely exposed to the air, it evaporates; that is, it passes into the gaseous state and mixes with the gases of the air. Even snow and ice give off water vapor, though in very small quantities. The quantity of water vapor which can enter a given volume of air is definitely limited. ”

“ We thus see that whirlwinds of great violence occur when the air is dry, and there can be no condensation. When, however, they are formed at sea, and occasionally on land, the air next the surface is saturated with moisture; and this moisture is condensed when it is carried to a great height, forming clouds, or falling in showers of rain and hail. This condensation of vapour is an effect, and not a cause, and takes place, not in the centre, but at the top or at the sides of the ascending column. ”

“ I saw four manner of dryings: the first was bloodlessness; the second was pain following after; the third, hanging up in the air, as men hang a cloth to dry; the fourth, that the bodily Kind asked liquid and there was no manner of comfort ministered to Him in all His woe and distress. Ah! hard and grievous was his pain, but much more hard and grievous it was when the moisture failed and began to dry thus, shrivelling.
These were the pains that shewed in the blessed head: the first wrought to the dying, while it had moisture; and that other, slow, with shrinking drying, [and] ”

“ A. A hot room is cooled more quickly by opening the lower sash; because the cold air can enter more freely by an under current, than by one higher up.
Q. Why does wind dry damp linen?
A. Because dry wind (like a dry sponge) imbibes the particles of vapour from the surface of the linen, as fast as they are formed. ”

“ The scattered live-oaks in the foreground, domineered by the will of the prevailing wind, have a half-frightened air; nothing of the repose of our maples, oaks, and white pines. The mountains themselves, rising with an almost monotonous uniformity of grade, are also burned as dry as a cinder, their dead-white rocks pallidly reflecting the remorseless sunlight. ”

“ You know a great many times when you go out into the wind how cold it feels, and yet if the wind would actually stop, you would think it warm. It is the wind that causes the rapid evaporation and makes the surface of the skin feel cold. As it is true that the moisture in the air acts as a blanket to us in our homes, it is likewise as true that the vapor in its natural form outside of the house acts as a blanket for the earth. ”

“ Relative humidity is the tendency of that vapor, be it great or small in quantity, to leak out of the vessel and show itself on the outside in the form of mist or dew. Sir John Herschel says, "As a general meteorological fact, there is not merely a want of accordance, but an actual opposition between both the diurnal and annual progress of the 'degree of humidity' or 'relative humidity' of the air and the 'tension of vapor' as indicated by hygrometric observation, a seeming paradox, but one very easily explained." ”

“ The water in all these rivers, lakes, and oceans is constantly rising into the air in what is called moisture or vapor. We can not see this moisture, neither can we see the air.
If the air is cold, moisture does not rise rapidly; but, as the air becomes heated, it takes up more moisture, so that the more heat there is in the air, the more moisture rises. ”

“ It usually rains more in mountainous countries than in those that are level, for the mountains, rising into the higher and colder regions of the atmosphere, chill and condense the vapors that are floating there, on the same principle by which a tumbler or a pitcher, made cold by iced water placed within it, condenses the moisture from the air, upon the outside of it, on a summer's day. ”

“ The modern science of ventilation concerns itself with these other factors; chief among them is the factor of moisture. As we shall see in the next chapter our bodies are constantly giving off from the lungs and by evaporation from the sweat glands water vapor into the air. This causes the humidity to go up rapidly in rooms where people are congregated, and particularly so where there are many people present. Also everyone gives off a great deal of heat. ”

“ RAIN “THE explanations of this morning account for the formation of clouds. A continual evaporation takes place on the surface of the damp earth as well as on the surface of the different sheets of water, lakes, ponds, marshes, streams, and above all the sea. The vapors formed rise into the air and remain invisible as long as the heat is sufficient. But since heat diminishes as the height increases, there comes a time when the vapors can no longer be kept in complete solution, and they condense into a mass of visible vapor, into a fog or cloud. ”

“ Who has not seen the window-panes of a heated room in cold weather bedewed with trickling moisture? The vapour of the room is in abundance, although invisible; but certain strata of the air thus charged come in contact with the cold panes, and lose a portion of their caloric, and with their caloric a portion of their vapour, (to which, perhaps, the respiration of a large party has contributed,) and this becomes condensed in the form of a visible fluid. ”

“ In inhabited rooms the moisture increases as much as the organic matter, and the condition of the air is similar to that of the evenings of summer: whenever the temperature goes down a little, there is a deposit of dew; but, when the warmth increases, the air is laden with moisture, and the condition resembles that near a warm close vegetation. In both cases ventilation is wanted. Our walls become saturated with moisture if they are porous, if not porous they are covered with streams of water. ”