Page:The American Cyclopædia (1879) Volume I.djvu/804

 768 AES calcium, 0-25; insoluble fibrine, 6; and water, 65-5 Of the starch 23 parts are obtained in the form of powder, and the other 3 are extract- ed in the form of paste from the parenchyma with boiling water. There is a so-called arrow- root brought from Florida, derived from a Florida Arrowroot (Coontie) and Fruit plant allied to the sago palm, and sometimes known as coontie. The plant grows among the everglades in great profusion. It is of an inferior quality, containing only 12 per cent, of starch. ARS. See ARS-SUR-MOSELLE. ARS.IMAS. See ARZAMAS. ARSENIC (Gr. apoevtriv or appevw<Jv, male, from its power in destroying), the common name of the white oxide of arsenic, or arseni- ous acid. In ancient times the name was ap- plied to a reddish-colored mineral compound of arsenic and sulphur, a substance in use then as a medicine, and also in painting. Metallic arsenic occurs native in veins in the crystal- lized rocks and older slates, and it is also pre- pared by subliming its oxide in presence of a reducing flux, and protected from the air. Many modern chemists do not regard it as a metal, though it is commonly treated as such. Con,biaed with oxygen, it unites with metals, forjiing arsenitesand arseniates of these metals, but is never itself the base of any salt. The ores of the metal are not therefore carbonates and sulphates of its oxide, but combinations of the metal itself with sulphur, forming the sul- phuret, and this combined with iron, cobalt, or nickel ; or they are oxides of the metal, or else compounds of its oxides with other metals. It is remarkable as the most volatile and one of the most combustible of the metals, is readily sublimed at a temperature of 360 F., apparently before it melts, and at a greater heat it takes fire and burns with a pale blue flame. In subliming, it gives out dense fumes of a pecu- liar garlicky odor, which distinguish it from other substances even when present in very minute quantity. It is more brittle than anti- mony, and may be reduced to fine powder in a mortar. Freshly prepared, it has a brilliant metallic appearance, a bluish- white color, and crystalline structure ; but in the air the metal becomes black and crumbles to powder. In water it may be kept without change. Its specific gravity is 5'96. It is the softeot of the ARSENIC solid metals, its hardness being rated on the mineralogical scale at 3'5. Arsenic readily combines as an alloy with other metals, render- ing them more fusible and brittle. Its presence is particularly injurious in iron ores, making the cast metal exceedingly brittle ; but it gives great fluidity to the melted iron, so that for line castings that do not require much strength, but sharply defined and delicate outline, it is sometimes desirable. It also increases the brightness of some alloys. It is not employed for any useful purposes in the metallic state. Arsenious acid, or white arsenic, is the most common combination of this metal. It is the sublimate, which escapes when arsenic is heated in the open air. The metal combines in the proportion of 1 equivalent with 3 of oxygen, the compound consisting of arsenic 75'76 per cent, and oxygen 24-24 per cent. The subli- mate, after exposure, is a white pqwder, but may be collected in the form of a glassy, trans- parent cake, or crystallized in octahedrons. It is partially soluble in boiling water, and less so in cold water. The solution is slightly acid, having but a feeble reaction upon litmus paper. The following are some of the most important tests given for detecting the presence of this poison : The blowpipe develops its peculiar odor, with little liability of mistake, in arsen- ical matters, heated on charcoal. It also re- duces the metal, and causes it to condense in the form of a metallic ring in the cold part of a glass tube, in which the substance containing arsenious acid has been placed with carbonate of soda and charcoal, and heated. The pres- ence of arsenic may be shown by this method, when the particle containing it is so small as to be invisible to the naked eye, in the follow- ing manner, communicated by Prof. A. K. Ea- ton of New York : The microscopic particle is placed in a bulb of a small glass tube, and a fine splinter of charcoal is placed by the side of it. The whole should then be thoroughly dried. The neck of the bulb is next to be drawn out to a capillary tube, and cooled. On applying heat to the matter in the bulb, this produces by sublimation a plainly visible arsen- ical ring in the fine bore of the tube. The acid is precipitated from its solutions by sulphuretted hydrogen in the form of tersulphuret of arsenic of a lemon-yellow color. This is a very accu- rate test, and is so delicate that the yellow tint is apparent when only -nr.Wff of the acid is present, and the precipitate when the arseni- ous acid is in the proportion of 1 part to 80,- 000 of water. It is precipitated in a white powder by excess of lime water, when forming f^f part of the liquid. Ammonio-sulphate of copper gives an apple-green precipitate, appa- rent when the acid forms Ty.irs P ar *- A s ^ more delicate test is that of Prof. Reinsch, to place a slip of bright copper leaf in the aque- ous solution acidulated with hydrochloric acid ; a gray film of arsenic is deposited upon the copper, showing the presence of less than Tinsvinnr P ar * f * no ac ^- I* ls affirmed that