Page:The American Cyclopædia (1879) Volume IX.djvu/380

IRON Ferric oxide 93-094 Ferrous oxide 6-810 Ferrous carbonate. ... 605 Calcic carbonate Silica 0-196 Ammonia trace. 100-000 Iron decomposes steam at a red heat and is converted into oxide, hydrogen being libe- rated. But hydrogen passed over oxide of iron nt a red heat reduces it to metallic iron, water being formed. The character of the ac- tion is here determined by the relative amounts of free hydrogen and steam. If the former predominates, reduction takes place; if the latter, oxidation. Dilute mineral acids dissolve iron, converting it into a ferrous salt, hydro- gen being evolved. Under certain circum- stances iron becomes "passive," and is not attacked by strong acids. This condition is brought about in various ways, and seems to be connected with a superficial oxidation of the iron. Iron burns with brilliancy in oxy- gen gas. Reduced by hydrogen from finely pulverized oxide, it burns readily in the air, taking fire spontaneously when the tempera- ture of reduction has not been too high, but otherwise requiring to be first ignited. Fer- rous oxide possesses so strong an affinity for oxygen that it is isolated with difficulty. Its salts are permanent when crystallized, but rapidly absorb oxygen when exposed to the air in solution. Ferrous carbonate occurs abun- dantly in nature. The most important ferrous salt is the sulphate, commonly called green vitriol or copperas, obtained as an incidental product in many metallurgical operations, and applied to manifold uses in the arts. It forms a number of double salts with other sulphates. Ferric oxide occurs abundantly in nature. (See IBON OEES.) It may be prepared artificially by precipitating the hydrate from solution and subsequently igniting it, and also by simple ig- nition of the sulphate or nitrate ; its powder is red. Ferric oxide and its salts are stable in the air, but part with a portion of oxygen when in contact with organic matter ; a famil- iar instance is the rotting of fabrics of cotton or linen by "iron mould." On this property depends the disinfecting power of iron com- pounds. Ferric oxide acts also as a carrier of oxygen. Bischof has shown that spongy me- tallic iron is a powerful disinfectant, probably first becoming oxidized itself, and subsequently parting with its oxygen to the organic mat- ter, then becoming again oxidized, and so on. Ferric oxide is largely used in the polishing of metals and glass. It forms salts which do not crystallize as readily as the ferrous salts. Ferroso-ferric oxide, generally called magnetic oxide, is abundant in nature, and may be re- pardcd as a compound of the two oxides, and its salts as compounds of ferrous and ferric salts ; it is perfectly stable ; its powder is black. Ferric acid is formed by heating together fer- ric oxide with saltpetre ; it forms salts which are very "unstable. Iron combines with sul- phur in two proportions, forming a proto- and a bisulphide. The former is largely used in the preparation of sulphuretted hydrogen for chemical purposes. The latter, known as py- rite or iron pyrites, occurs abundantly in na- ture, and is used largely as a source of sul- phur in the preparation of sulphuric acid. Iron forms a definite compound with nitro- gen, Fe,N 3 ; but it is doubtful whether nitro- gen plays any part in the manufacture of iron or steel. Compounds of carbon, phosphorus, and silicon with iron also exist ; the effect of these substances on the properties of iron is discussed below. The compounds of iron with chlorine and cyanogen are of great importance in chemistry and in the arts. There are two chlorides, FeCla and FeaCle, corresponding to the two oxides, and two double compounds with cyanogen, potassic ferrocyanide or yel- low prussiate of potash, K<FeCoN, and potas- sic ferricyanide, or red prussiate of potash, KFeCN, which are valuable chemical re- agents. The ferrocyanide of iron, or Prussian blue, Fe<, FeCNe, is formed by precipitation of a solution of a ferric salt with yellow prussiate of potash. Iron is used in medicine as a re- constructive tonic. It is an important constit- uent of the animal tissues, and under ordinary circumstances the supply normally present in the food is equal to the. demand; but when the number of red blood corpuscles, which contain much iron and are the special carriers of oxygen, is diminished, then their re-forma- tion may be promoted by the administration of iron preparations. This condition (anaemia) is the real indication for iron, most of the special diseases in which it is used being dependent upon or accompanied by this condition. Hence it is largely used not only in ana?mia, but in neuralgic affections, dropsy, Bright's disease, scrofulous affections, incipient phthisis, haemor- rhages, the various diseases of females, in the convalescence from acute diseases, and in the protean forms of debility and weakness. A few of the salts are astringent, and a portion of their effect is probably due to their local ac- tion upon the stomach. These may be used not only as reconstructive agents, but to check discharges and arrest haemorrhage. Iron is absorbed in small quantity, so that a consider- able proportion of every dose passes through the bowels unappropriated. It may be detected in the urine, and the amount normally pres- ent has been found increased in the milk of animals to which iron has been administered. The bodily temperature is raised, the pulse quickened and strengthened, and the appetite and nutrition improved by its administration. Headache and constipation are the consequences of too large doses or too long continued use. The number of preparations in use is exceed- ingly and unnecessarily large, and constantly increasing. Among them are metallic iron, a grayish powder; the protocarbonate, in pills and mixture; the sulphate; hydrated oxide, usually called subcarbonate ; tincture of the chloride; wine of iron; tartrato of iron and potassa; phosphate, lactate, and iodide ; citrate