492 BUILDING MATERIALS. Parliament, is preferred; it is very close and compact, sufficiently soft to be easily sculptured, but retains a sharp outline. Many fine-grained, porous, calcareous and magnesian stones have the inconvenience of splitting into flakes after a few years' exposure; this generally occurs from the absorption of water, and its expansion when the moisture thus absorbed becomes frozen during winter. A simple and ingenious mode of ascertaining whether a building stone is liable to this defect was invented by Brard :-It consists in taking a smoothly cut block of the stone, one or two inches in the side, and placing it in a cold saturated solution of sulphate of sodium. The temperature of the solution is gradually raised to the boiling-point, it is allowed to boil for half an hour, and then the stone is left to cool in the liquid. When cold, it is suspended over a dish, and once a day for a week or a fortnight plunged for a few moments into a cold saturated solution of the sulphate of sodium, and is then again freely suspended in the air. The sulphate of sodium crystallizes in the pores of the stone, and splits off fragments of it. A similar experiment is made upon an equal sized mass of stone which is known to be free from this defect. By the comparative weight of these fragments in the 1000 obtained by simple inspection of the subjoined table. The results are, however, apt to be inaccurate, if large quantities of magnesian salts are present. (D. Campbell, Phil. Mag. 1850, xxxvii. 171.) Sometimes the water exceeds 16° in hardness; in that case it should be diluted with an equal measure, or, if necessary, with twice, or even with thrice its bulk of distilled water. grain-measures of the diluted water are then to be tested as usual, and the number of divisions of the soap-test employed is to be read off, and the degree of hardness corresponding to it is noted from the table. This degree must be finally multiplied by 2, by 3, or by 4, according to the extent to which the water had been previously diluted. Clark's Table of Hardness of Water. PHOSPHATES OF CALCIUM. 493 two cases the tendency of the stone to the defect in question may be estimated. A stone which is placed in a building conformably to its position in the quarry, so that its seams shall lie horizontally, is much less liable to injury from the weather than where this point is neglected. In the selection of a building-stone, regard must be had not merely to its durability, but also to the locality in which it is to be placed. A stone which, like a magnesian limestone, may endure unchanged for ages in the open country air, may yet in the atmosphere of a large city become rapidly disintegrated, owing to the action of the sulphuric acid produced by the immense quantities of coal which are burned. Decay from this cause is strikingly shown in the stone used in some parts of the new Houses of Parliament, and still more so in the new buildings in Lincoln's Inn. A valuable report upon the composition and quality of various kinds of building stones was made to the British Government in 1839, upon the occasion of the rebuilding of the Houses of Parliament. The other varieties of building stones are mostly siliceous. To this class belong all the sandstones, which consist chiefly of grains of silica united by a cement more or less ferruginous. The durability of the stone depends mainly upon the character of this uniting material. Many igneous rocks, such as porphyry, basalt, and more especially granite, are also used for building purposes; but from their hardness, they are seldom wrought, except when, as in quays, bridges, or causeways, the constant wear is unusually great, and where softer though less expensive materials would soon be destroyed. (657) PHOSPHATES OF CALCIUM.-The most remarkable of the phosphates of calcium is that known as the bone phosphate (Єa", 2 PO1, or 3 CaO,PO; Comp. in 100 parts, EaÐ,54'2; PO, 45'8), so named from its forming the principal earthy constituent of the animal skeleton. It is easily procured by adding chloride of calcium, drop by drop, to a solution of phosphate of sodium in excess, when it falls as a gelatinous precipitate with 2 H2O. It may also be obtained from calcined bones by digesting them in nitric acid, and precipitating the filtered solution by caustic ammonia. This phosphate is insoluble in water, but is readily dissolved by acetic, and the stronger acids. It occurs native as a white amorphous mineral, known under the name of phosphorite. In the Norfolk crag considerable deposits of brown rounded pebbles occur, known under the name of coprolites, from the erroneous supposition that they were the fossilized dung (kówρoç) of extinct animals: they contain a large proportion of phosphate of calcium 494 CHARACTERS OF THE SALTS OF CALCIUM. mixed with carbonate and fluoride of calcium. In the green-sand formation near Farnham, and in other localities, nodules chiefly composed of phosphate of calcium are also found abundantly. A tribasic phosphate of calcium occurs naturally crystallized in hexagonal prisms, which, when colourless, are called apatite; when of a green colour it is termed moroxite; in these minerals three atoms of the phosphate are associated with one atom of chloride and fluoride of calcium: 3 (Ea, 2 PO1), Єa (CIF). If bone-ash be fused with about 4 times its weight of chloride of sodium, and allowed to cool very slowly, delicate crystals having the form of apatite are found lining the cavities contained in the mass (Forchhammer). When rhombic phosphate of sodium in solution is added drop by drop to an excess of chloride of calcium, a semi-crystalline precipitate falls, which, according to Berzelius, consists of (2 Ea"HP 3 H2O). 49 Several other phosphates of calcium may be formed, corresponding in composition to the various phosphates of sodium. The soluble acid phosphate, or superphosphate of lime (Ca′′H 2 PO or CaO, 2 HO,PO), is prepared by treating bone-earth with twothirds of its weight of oil of vitriol, as in the preliminary stage of the extraction of phosphorus. It is largely manufactured as a manure for turnips. 2 3 (658) A.double borate of calcium and sodium, or boro-natro-calcite, [2 (NaЄa"3 B→) 3 B2O. 18 H2O], is found at Iquique,in Peru, in the form of rounded nodules, composed of fine silky needles. It is but sparingly soluble in hot water, to which it communicates an alkaline reaction; but it is easily dissolved by diluted acids. This mineral has recently been imported into this country to some extent for the preparation of borax, which is easily obtained from it by dissolving the compound in hot diluted hydrochloric acid, and precipitating the calcium as carbonate by the addition of carbonate of sodium; the clear, supernatant liquid on evaporation yields crystals of borax, whilst chloride of sodium remains in solution. (659) CHARACTERS OF THE SALTS OF CALCIUM.-The salts of calcium are colourless. They give no precipitate with ammonia, but yield a white precipitate of carbonate of calcium, with the carbonates of the alkali-metals. Solution of sulphate of calcium produces no precipitate; the calcium salts are thus distinguished from those of barium and strontium: they yield no precipitate with hydrosulphate of ammonium. Oxalate of ammonium, even in very dilute neutral or alkaline solutions of salts of calcium, throws down a white oxalate of calcium, which is soluble in nitric and METALS OF THE EARTHS. hydrochloric acids, but not in acetic acid. 495 Salts of calcium give a greenish-yellow tinge to flame, and when examined by the spectroscope may be recognized by a bright line in the orange, and a broad rather less luminous band in the green; fainter lines are also visible in the red; and occasionally a bright blue band is seen. Estimation of Calcium.-In the determination of calcium for analytical purposes the oxalate is the precipitate usually employed; but before weighing it is heated to dull redness, so as to convert the oxalate into carbonate of calcium: 100 parts of the carbonate represent 56 of lime. If no other base be present, calcium may also be estimated in the form of sulphate. If the calcium be not already in the state of sulphate, the salt is heated with an excess of sulphuric acid, and ignited; when cold, it is weighed: 100 grains of sulphate of calcium represent 41°18 of lime. Magnesium will be described in the group containing zinc and cadmium (683 et seq.). CHAPTER XIV. GROUP III. METALS OF THE EARTHS. § I. ALUMINUM: Al"" = 27.5, or Al = 13'7. Sp. Gr. from 25 to 267. Sp. Heat, 0'2143. Electric Conductivity at 67°.2, 33.76. Atomic Vol. solid, 10:56. (660) THE pure earths are white, insipid, insoluble compounds, the oxides of metals which possess a high attraction for oxygen. A single oxide only of each metal of this class is known, except in the case of cerium. (See p. 338.) Of these metals the most abundant and important is ALUMINUM, which derives its name from alum, into the composition of which it enters. Indeed, alumina (the oxide of aluminum) constitutes about 10 per cent. of this salt. Preparation.-1. Aluminum was originally procured by Wöhler, by decomposing chloride of aluminum in a porcelain or platinum tube by means of potassium. He obtained it first as a steel-grey powder, and subsequently in malleable globules. In the pulverulent form it is gradually oxidized by boiling water, and more rapidly by alkaline solutions. When heated in this form in oxygen gas, it takes fire and burns with a vivid light, emitting so intense a heat as to fuse the alumina, which forms a yellowish mass, in colour and hardness resembling native crystallized alumina as it exists in corundum. 496 ALUMINUM-PREPARATION. 2.-Bunsen obtains aluminum by the electrolytic decomposition of the double chloride of sodium and aluminum (2 NaCl, Al,Cl). This salt melts at about 356°, and readily furnishes aluminum by a process similar to that adopted in the case of magnesium (683): but as the aluminum is heavier than the fused salt, it is more easily collected than magnesium. 3.-Aluminum may be prepared in the laboratory, by the method of Deville (Ann. de Chimie, III. xliii. 5).—Into a wide tube of hard glass of an inch or an inch and a half in diameter, about half a pound of dry chloride of aluminum is introduced, and kept in its place by plugs of asbestos; a current of dry hydrogen, perfectly free from air, is transmitted, and the chloride of aluminum is very gently heated; in this way traces of hydrochloric acid and chlorides of sulphur and silicon are expelled. Three or four small porcelain trays, each containing 40 or 50 grains of sodium, freed from adhering naphtha by pressure between folds of blotting-paper, are then introduced into the tube ; the current of hydrogen is still maintained, and heat is applied to the part of the tube which contains the sodium. This end of the tube must be slightly elevated, in order to prevent the melted chloride of aluminum from running down upon the sodium; in which case the heat emitted is so intense as to crack the tube. When the sodium is melted, the chloride of aluminum is gradually distilled over by the application of a regulated heat, and is reduced with vivid incandescence. The aluminum is condensed in the porcelain trays, in which also a double chloride of aluminum and sodium collects around the reduced aluminum. These trays and their contents when cold are withdrawn from the glass tube, and placed in a porcelain tube through which a current of hydrogen is transmitted, whilst the tube is raised to a bright red heat; the aluminum fuses into globules in the porcelain trays; and by fusing it once more in a porcelain crucible under a layer of the double chloride of aluminum and sodium, a button of pure aluminum is obtained. Messrs. Bell of Newcastle have carried out the process of Deville as a manufacturing operation. They prepare an aluminate of sodium from Bauxite, an aluminous ore of iron (663), and precipitate the alumina as hydrate, by means of hydrochloric acid. The precipitated hydrate of alumina is then mixed with common salt and charcoal, made into balls the size of an orange, and dried. These balls are placed in vertical earthen retorts heated to redness, and through them dried chlorine is transmitted. A double chloride of aluminum and sodium (2 NaCl, Al,Cl) distils over. This double salt is heated with sodium in a reverberatory furnace, and |