Page:Popular Science Monthly Volume 14.djvu/259

Rh of the dome is from seven to eight inches at the base, and its height is about the same. The inhabitant of this most curious structure is thus described by our author: "The fore-part of the body, cephalothorax, is of a golden-yellow color, bordered and marked with blackish bands. The legs are of a delicate green, having the thighs marked by blackish longitudinal bands, and blackish annuli at the joints. On the back of the abdomen the colors within the blackish marginal lines are as follows: at the base, next the cephalothorax, a snowy white; the middle lobes are a light yellow, the lower lobes and the cruciform figure are a golden yellow. The bands and markings on the side of the abdomen are in the following order from the top, viz., crimson, white, dark green with light-green edges, blackish to dark green, yellow." But in the mind of the araneologist the special interest of the basilica spider is not its architectural skill, not its beautiful markings, but the fact that it seems to form a link between the orb-weaving and the line-weaving spiders.

Manufacture of Sea-Salt in San Francisco.—At Rock Island, in the bay of San Francisco, works have lately been established for reducing salt from sea-water by solar evaporation. The process of evaporating the salt-water is described as follows in the Engineering and Mining Journal: "The water is let into a large reservoir at high tide, and thence passed into a series of other reservoirs, until it has traversed a distance of fifteen to twenty miles, in the mean time steadily increasing in strength and dropping its limy impurities. In the fourth reservoir the specific gravity is 16°, and it leaves the seventh when it is 25°. Pure chloride of sodium begins to form when the brine attains this density, and continues to do so until it has attained 29°. During the strengthening of the sea-water from its natural specific gravity of about 1.03 to 25, the sulphate of lime held in solution crystallizes and settles to the bottom. It is not until a specific gravity of 29 is reached that chloride and sulphate of magnesia, bromide of soda, and chloride of potassium, begin to concrete. These being the principal if not the only impurities, with the exception of a little water, the manner of securing pure salt appears very simple. When at 25°, the pickle is run into crystallizing ponds or vats, some of which are simply the earth hollowed for the purpose; others are boarded on the bottom, while a third is made wholly of boards. In these the brine is allowed to remain until it is 28°, when the salt which has formed in the bottom is shoveled into baskets, loaded on cars, and conveyed to another part of the island nearer the wharf, where it is piled up in great pyramidal-shaped mounds. These remain exposed to the sun and weather for a year, which whitens and purifies the crystals preparatory to grinding."

Atmospheric Electricity and Plant-Growth.—Atmospheric electricity is, according to M. Grandeau, a powerful agent in the process of assimilation in plants. Plants protected from its influence build up fifty to sixty per cent, less of nitrogenous matter than those subject to ordinary conditions; the proportion of ash is higher and of water lower. In the author's experiments different species of growing plants were inclosed within an electric screen consisting of four triangles of iron. The plants experimented upon were maize, tobacco, and wheat—two specimens of each—of which the one was screened from atmospheric electricity, the other not. The results of these experiments agree fully with the discovery made some time ago by Berthelot, that free nitrogen unites with organic matter under the action of electric currents not only from ordinary induction-coils, but even from feeble voltaic batteries. The proportion of nitrogen thus fixed in seven months in paper and dextrine was 1.92 thousandths.

Pure Teas.—The Chinese minister at Washington, Chin-Lan Pin, was lately visited by a delegation representing a firm of tea-importers in Baltimore, who wished to learn his views regarding the importation into this country of pure teas. The minister in his reply said that the various brands of tea sold in America and Europe are unknown to and not used by the tea-consumer in China. They are specially prepared by the Chinese tea-exporters for the foreign market. They are colored by the use of