Although water possesses a specific gravity eight hundred and fifteen times greater than that of air, yet it can rise into the air as into a vacuum, and mingle amongst it by the same law that gases diffuse through each other. It is this property of water which enables us to have clean and dry linen, for if it were other wise, if water was the same as oil, our wet clothes would have to be converted into fuel and burned in the fire be:ore we could expel the moisture from them. Were it not for this property of water, the calico printers and woolen dyers could never dry their pieces in shade, sunshine, or stove room. When wet goods of any kind are submitted to heat in a room, they soon become dry, because the air receives the moisture and retains it in its soft embrace, thus enabling us to obtain dry goods and dry clothing by the property of evapora tion which belongs to water, and the la'x of gaseous absorption which reigns among the gases. A curious property of the evaporation of water, discovered by Dr. Dalton is, that the quantity which will rise in a confined space is the same, whether that space be a vacuum or be already filled with air, hence it is only ne cessary to know what quantity of vapor rises into a vacuum at any particular temperature, to know what quantity will rise into the air. Thus the vapor of water which rises into a vacuum at the temperature of 80 , depresses the mercurial column one inch; its tension is one-thirtieth 0 the usual tension of air. If water at 80 be admitted into dry air it will increase the tension of that air one-thirtieth if the air is confined; or increase its bulk one thirtieth if the air is allowed to expand. A certain fixed quantity 01 the vapor of wa ter, therefore, can only rise into a certain fix ed quantity of air, hence the air of rooms em ployed for drying goods may become so satu- rated with moisture, that the fuel may be ex pended foolishly in trying to expel the mois ture from the goods when it is impossible for the air to take it up, and hence the evapora tion of water is greatly facilitated by a current of air. This is the philosophic principle of evaporation embraced by Bessemer, and that mentioned under the head of Recent Foreign Inventions, in this number of the Scientific American, for evaporating sugar syrups. In evaporating by means of hot air, as in drying goods in the stove rooms of calico print and bleaching works, when the rooms are heated by flues running along the floors, it should not be forgotten by those who have charge of such drying establishments, that a certain time must elapse after the goods are placed in the rooms, before the air is saturated with humidity ; due discretion must therefore be exercised not to let any of the hot air es cape until it is saturated with moisture. It has been proposed to us more than once, to employ hot air in raising steam, under the mistaken idea that more steam could be ge nerated with less fuel by the passing of such a rarified hot body through the water. But in evaporating water by heated air—the way wet goods are dried—the vapor itself carries off exactly the same quantity of heat as if it were produced by boiling the water at 212 , while the air associated with it requires also to have its temperature raised, thus requiring more fuel, hence water can never be evapora ted in a drying room, with so small an ex penditure ot fuel, as steam can be generated in a close boiler, These facts are well wor thy of attention, inasmuch as they relate to different branches of business, in which very many of our people are interested.
This article was originally published with the title "Drying Goods in Warm Rooms"