Page:Popular Science Monthly Volume 14.djvu/706

688 the "superheater," which imparts to it the necessary temperature. The iron articles to be acted on are placed in a chamber built of fire-clay, and the steam being admitted to it a coating of magnetic, or black, oxide of iron is produced on the surface. And now for the result. The article has a dull black appearance, and is susceptible of a high degree of polish. The surface coating is absolutely adherent, and is so hard that it is not removable by ordinary methods, for instance, an iron rasp has no effect on it; and the same is to be said of all the agents which under ordinary conditions oxidize iron. Salt or fresh water, vegetable acids, and even the London atmosphere, are unable to produce the slightest tarnish. Iron vessels which have contained water for weeks are entirely free from rust. Iron piping and ornamental castings, which have for months lain among the wet leaves in the garden outside Professor Barff’s laboratory, are unchanged. The cost of the process is trifling, less than that of "galvanizing." The sanitary and domestic uses of iron thus prepared are numerous, as for water-pipes and cisterns and for cooking apparatus.

Plants and Atmospheric Humidity.—Two questions of considerable interest, viz., that of the effect of living plants on the atmosphere of houses and that of the relations between forests and atmospheric humidity, appear to have no little light thrown upon them by the ingenious researches of Dr. J. M. Anders, published in the "American Naturalist." We can not state with any degree of fullness the author's experiments to determine the amount of vapor transpired by plants in proportion to the area of their leaf surface. Suffice it to say that according to these experiments the "Washington elm," at Cambridge, Massachusetts, with its 200,000 square feet of leaf surface, would transpire seven and three quarter tons of watery vapor in twelve diurnal hours of clear weather. Carrying the calculation further, a grove consisting of 500 trees, each with a leaf surface equal to that of the elm mentioned, would return to the atmosphere 3,875 tons of aqueous vapor in twelve hours. In-doors, transpiration is during the day only about one half as active as in the open air, but at night it is about equal in the two situations: hence the transpiration of a plant in-doors is more than one half as much in twenty-four hours as it would be outside. It follows that growing plants increase the humidity of the atmosphere in a closed room. This point is very important where rooms are heated by hot air furnaces. In such apartments the air is drier than in apartments heated by a stove or an open fireplace. In a dry atmosphere of the temperature of 65° to 68° Fahr. a great demand is made upon the system to supply the air with moisture, the skin and pulmonary mucous membrane are dried, and a condition is induced which is expressed in irritability of the nervous system, paleness and susceptibility of the skin to cold, liability to pulmonary diseases, and, in short, deterioration of all the functions. Now, if the presence of a certain number of thrifty plants in an occupied apartment, warmed by dry air, would have the effect of raising the proportion of aqueous vapor, it is clear that plants in rooms heated by a hot-air furnace would, in an hygienic point of view, be of very decided value, since they may become the means of obviating very distressing symptoms, or even disease itself. As for the question of the relation of forest growth to atmospheric humidity and consequently to rainfall, such relation would appear to be clearly established by the author's researches.

Source of Organic Matter in Igneous Rocks.—Associated with the sheet of trap-rock which forms the First Newark Mountain, New Jersey, there occurs near Plainfield an amygdaloid trap passing into a metamorphosed shale. Many of the cavities in the amygdaloid rock are filled with a jet black carbonaceous mineral, closely resembling the "albertite" of New Brunswick. Above the amygdaloid is a metamorphosed shale, traversed by seams and fissures, which are frequently filled with the same albertite like mineral. Finally, resting on these metamorphosed beds are slates, shales, and sandstones, which contain fossil fishes and an abundance of obscure vegetal remains. From this state of facts Mr. J. C. Russell ("American Journal of Science" for August) infers that the organic bodies in the