240 



THE POPULAR EDUCATOR. 



oxygen causes it to unite with that element and become the 

 next higher oxide ; but in a hydrated form it is precipitated 

 from any ferrous solution by potash. 



Ferric oxide (Fe 2 O 3 ) appears crystallised in nature as specular 

 iron ore, and amorphous as red haematite. It may be prepared 

 artificially by precipitation from a solution of ferric sulphate or 

 chloride by ammonia, and heating the precipitate. Both the 

 above oxides are bases for corresponding salts. 



Ferrous sulphate (FeSO 4 -f 7H 2 O) is copperas or green vitriol; 

 it is the result of the action of sulphuric acid on metallic iron. 

 If it be permitted to absorb oxygen it changes colour, and 

 becomes partially Ferric sulphate (Fe 2 3S0 4 ). Green vitriol is 

 used with astringent matters as a black dye. With gallic acid 

 it forms ink. 



Ferrous chloride (Fe 2 Cl). When iron is acted upon by hydro- 

 chloric acid, and solution evaporated, green crystals of this salt, 

 containing four molecules of water of crystallisation, are formed. 



Ferric chloride (Fe 2 Cl a ) is produced when hydrochloric acid 

 acts upon ferric oxide. 



Ferric acid has never been prepared, it is very unstable ; but 

 if nitre and ferric oxide be fused together, potassium ferrate 

 (K 2 FeO 4 ) is formed. This metal forms many other salts, but 

 they are of no great interest. 



The ferrous or protoxide salts give green solutions ; with 

 alkalies they yield white precipitates, and a light-blue colour 

 with potassium ferro-cyanide, which rapidly becomes dark. If 

 their solution be slightly acid, sulphuretted hydrogen has no 

 effect upon them. 



Ferric or peroxide salts are of a reddish-brown colour, and 

 such is the colour of their 

 precipitate with the various 

 alkalies. 



Potassium sulpho-cyanide 

 in neutral solutions gives a 

 thick precipitate of a dark- 

 red colour, similar to that 

 of blood. Potassium ferro- 

 cyanide affords a copious pre- 

 cipitate of a rich dark-blue 

 oolour. 



It should be said lhat 

 under the action of the blow- 

 pipe both classes of salts 

 act alike, namely, with them 

 a borax bead becomes green 

 in the reducing flame, which 

 all but loses its colour when it is exposed to the oxidising flame. 



TITANIUM. 



SYMBOL, Ti COMBINING WEIGHT, 50. 



This is a rare metal, generally associated with iron. They 

 appear together in Rutile, and it would seem that a minute quan- 

 tity of titanium is disseminated through the clay iron ore ; for 

 in the cindery coating of the crucible of a smelting furnace, 

 after many years' work, there appear beautiful cubic crystals of 

 a red metallic substance, which are found to be a compound of 

 nitrogen and titanium. Though this metal is found with iron, 

 it bears a close analogy to 



TIN. 



SYMBOL, Sn COMBINING WEIGHT, 118 SPECIFIC GRAVITY, 7'3. 



The only ore of tin of importance is tin-stone, which is the 

 tinoxide of the metal (SnO 2 ); it is by no means widely dis- 

 tributed, only being worked in three or four localities. The 

 mines of Cornwall furnished the Romans with their supply, 

 and still yield 6,000 tons annually. The island of Banca, in 

 the East Indies, is almost a block of very pure ore. Mexico 

 also possesses tin mines. When a stream of water wears away 

 the rock through which a vein of tin passes, the ore is found 

 water- worn in the bed of the stream. This is the most valuable 

 ore, and goes by the name of stream-tin. The reduction of the 

 metal is easily accomplished, since the washed and pure ore has 

 only to be submitted to heat in a reverberatory furnace, mixed 

 with coal and a little lime. The ore gives up its oxygen to the 

 coal, and the lime, with some silica, which is unavoidably pre- 

 sent, forms a fusible slag. The metal sinks to the bottom of 

 the furnace, and the slag swims on its surface. 



Tin is a white brilliant metal, capable of being beaten out 

 Into "foil," and sufficiently duotile to allow of its being drawn 



Fig. 51. SECTION OF KEFISIHG FUKNACE. 



out into wire. When bent it emits a " crackling " noise. It 

 melts at 235 Cent., and can be volatilised, though with difficulty. 

 The air has but little effect on it ; but when heated to a high 

 temperature it combines with oxygen, burning brilliantly into a 

 white powder, stannic oxide (SnO 2 ). 



It is chiefly used in commerce as a covering to sheets of iron. 

 The best iron is used, and by a series of processes is rendered 

 chemically clean ; the sheet is then immersed in melted tin, and an 

 alloy is formed at the surface of the iron. The sheet is dipped 

 a second time and the superfluous metal allowed to drain off. 



If the surface of a sheet of tin be sponged with a mixture of 

 two parts nitric acid, two of hydrochloric, and four of water, 

 the crystalline appearance known as moiree metallique is pro- 

 duced. The plate must be gently heated before the application 

 of the acid, and quickly plunged into water and varnished. 

 Different effects may be produced by using coloured varnishes. 

 Alloys of Tin. Britannia metal is equal parts of brass, tin, 

 antimony, and bismuth. Pewter is 4 parts of tin and 1 of 

 lead. Solder is 2 parts of tin and 1 of lead. Bell metal is 78 

 of copper and 22 of tin. Gun metal is 90 of copper and 10 of 

 tin. Bronze contains less tin than gun metal, and usually 3 or 

 4 per cent, of zinc. Speculum metal, which admits of a high 

 polish, and is used for the mirrors of reflecting telescopes, con- 

 sists of 2 parts of copper and 1 of tin. For silvering mirrors, 

 an amalgam of tin and mercury is employed. A sheet of tin- 

 foil is laid on a level marble slab, and covered by clean mercury ; 

 the superfluous quicksilver runs into a groove cut in the stone 

 round its edge. When the mercury remains on tho foil in a 

 layer of the thickness of half-a-crown, a perfectly dry and clean 



sheet of glass is carefully 

 slid over the mercury, be- 

 ginning at one end of the 

 slab by dipping the edge of 

 the glass beneath the sur- 

 face of the quicksilver thus 

 all air-bubbles are excluded ; 

 the glass is coveted with 

 flannel and weighted, the slab 

 being inclined to allow the 

 mercury to drain off. This 

 inclination is increased until, 

 in a month, the glass is ver- 

 tical, and is then in a fit con- 

 dition to frame. 



Tin forms two oxides : 

 Stannous oxide (SnO) is 



prepared as a white hydrate, by precipitation from a solution 

 of stannous chloride by an alkaline carbonate. When moist 

 it absorbs oxygen, and becomes 



Stannic oxide (SnO 2 ), which is found as tin-stone. It may be 

 artificially prepared by the action of nitric acid on tin, or by 

 adding an alkali to a solution of a stannic salt. It is remark- 

 able, that when prepared in the former way it is insoluble in 

 hydrochloric acid, whereas, in the latter case, it is readily 

 soluble. 



When tin is treated with nitric acid, a white crystalline in- 

 soluble mass is formed 



Metastannic add, which, when heated to 100 Cent., parts 

 with some of its water and becomes 



Putty powder, which is much used in making enamels. These 

 oxides of tin are of great use to the dyer as mordants. 



Bisulphide of tin (SnS 2 ) is mosaic gold, a powder which closely 

 resembles the precious metal, and is used in decoration. 



The purple of Oassius appears when stannous chloride (SnCl 3 ) 

 is added to a solution of chloride of gold. 



TUNGSTEN. 



SYMBOL, W COMBINING WEIGHT, 184. 



This metal, combined with iron, occurs in the mineral wolfram. 

 It has been lately discovered that a little of it in steel greatly 

 increases the hardness of that substance. 



Tungstic acid (W0 3 ) is obtained as a yellow powder when 

 native tungstate of lime, scheelite, is treated with nitric acid; 

 with sodium, the tungstate of soda is formed, which is mixed 

 with starch, and used by the laundress to render muslins, etc., 

 uninflammable. 



Molybdenum and Vanadium are closely allied to tungsten, butj 

 as yet, have no commercial value. 



