96 



THE POPULAB, EDUCATOR 



reduced to powder in an agate mortar. An alkaline silicate 

 is formed when this powder is heated with three times its weight 

 of sodium or potassium carbonate. If this be added to an 

 excess of diluted hydrochloric acid, the acid combines with the 

 metal, and although the silica is thus ejected from its combina- 

 tion, it does not precipitate ; but if heat be now applied, when 

 the solution has reached a certain point of concentration, the 

 silex is again rendered insoluble, and becomes a gelatinous mass. 

 By still continuing' the heat until much of the water is driven 

 off, then the chloride of the metal may be washed out, and the 

 pure silex again remains in its insoluble form. When rendered 

 anhydrous, it is a white, light powder. 



All spring or well waters contain silica, either in a free state 

 or in solution as an alkaline silicate, and by this means it enters 

 into many vegetable and animal organisms. 



Silicon Chloride (SiClJ. As the corresponding boron com- 

 pound, this is got by heating silica mixed with carbon in a cur- 

 rent of chlorine. It is a liquid, and has the same remarkable 

 action with water as the boron chloride, being decomposed into 

 hydrochloric acid and silicic acid. 



Silicic Fluoride (SiF 4 ) is the gas by the formation of which, 

 with hydrofluoric acid, the etching of glass is effected. 



There is also a sulphide of silicon, which is a solid. When 

 thrown into water it decomposes, sulphuretted hydrogen 

 escapes, and soluble silicic acid is taken up by the water. 



METALS. 

 GENERAL PROPERTIES, ETC., OP METALS. 



It was stated in an early lesson that the distinction between 

 a metalloid and a metal was not very decided. Perhaps the 

 definition of a " metal," which will be finally adopted, will be 

 that it is " a body which, when in solution, is carried with an 

 electric current which traverses that solution ; " but on referring 

 to the analysis of water by the voltameter, it will be noticed 

 that hydrogen passes ivith the current ; hence it is necessary, if 

 this definition be adopted, to class that gas among the metals. 

 There is no reason for doubting that if hydrogen could be con- 

 densed into a solid it would exhibit metallic lustre and the 

 other properties common to all metals. 



The chief properties which characterise metals are 

 Metallic Lustre. This lustre, however, ia not peculiar to the 

 class, for it is shared by iodine and graphite. 



Moreover, if most metal? bo procured in a state of fine sub- 

 division they are lustreless. This is prominently tho case with 

 gold, which, when painted on china, in a chemical solution, and 

 then burnt, comes out of the furnace dull green, and the well- 

 known lustre of gold does not appear until the painted portions 

 have been burnished. 



Opacity. Metals are usually considered opaque, but this is 

 not absolutely true, for gold, if not more than auiJ ' ulHJ th of an inch 

 thick, permits green light to pass through it, and other metals 

 exhibit a similar imperfect opacity when reduced to very thin 

 leaves. 



Hardness. Steel, which is a compound of carbon and iron, is 

 the hardest of the metals, and the rest pass through every degree 

 down to potassium, which may be moulded by the fingers as if 

 it were putty. The hardness of a metal may be greatly in- 

 creased if its temperature be raised to a certain point and then 

 suddenly cooled by plunging it into water. Many of the hard 

 metals are sufficiently elastic to be sonorous when struck. 



Brittleness and tenacity are closely connected. Many of the 

 metals, such as bismuth, antimony, arsenic, are so brittle as to 

 admit of being pounded in a mortar, and many, such as steel, 

 iron, copper, can be made brittle by suddenly reducing their 

 temperature. Others, again, exhibit this quality only at certain 

 temperatures : for instance, zinc, which cannot be bent without 

 danger of cracking, is readily worked at a temperature of about 

 115 Cent. ; and on the other hand, brass an alloy of zinc and 

 copper becomes brittle as it approaches a red heat. 



Tenacity is the property which gives to metals their power of 

 supporting a strain. Iron possesses it in the most eminent 

 degree, hence the great value of this metal. 



Malleability and Ihtctility. Possessing the one property, the 

 metal may be beaten or rolled into very thin leaves ; with the 

 other, it admits of being drawn into wire. Gold, silver, copper, 

 and platinum are very malleable. Gold may be beaten out into 

 leaves so thin that 280,000 only make an inch. These metals, 

 and iron, are the five which are notably ductile. Wollaston, by 



placing a wire of platinum in the axis of a bar of silver, and then 

 in the usual way that is, by drawing it through holes in a 

 steel plate procured a very fine wire, the centre of which was 

 one much finer of platinum. By dissolving the silver away with 

 nitric acid, this was exposed, and found to be ^o^th of an inch 

 in diameter. The foregoing qualities are greatly dependent on 

 tho texture of the metal, and the dissolving texture is greatly 

 affected by the manipulations which the metal undergoes in its 

 reduction from the ore. Thus cast-iron is brittle, so is hard 

 steel ; yet steel is capable of being made into watch-springs, 

 and iron can be drawn into very fine wire. 



Specific Gravity is the relation which the weight of a body 

 bears to the weight of an equal volume of water. The metals 

 differ greatly in their specific gravities : 



Platinum, 2T5. Silver, 10'53. Arsenic, 5'96. 



Osmium, 2T4. Bismuth, 979. Aluminum, 2'56. 



Indium, 21'1. Copper, 8'95. Magnesium, 174. 



Gold, 19-34. Cobalt, 8"95. Sodium, 0'972. 



Mercury, 13'59. Iron, 7'8t. Potassium, 0'865. 



Lead, 11'36. Tin, 7'29. Lithium, 0'593. 



Zinc, 7-14. 

 The lightest metals are the most easily attacked by oxygen. 



Fusibility. The following table gives the " melting points " 

 of the chief metals : 



Mercury, 394'Cent. Tin, 228. Copper, 1091. 



Potassium, 58f>. Lead, 325". Gold, 1102". 



Sodium, 976'. Zinc, 412. Cast-iron, 1530. 



I Silver. 1023. 



while platinum requires the intense heat of the oxy-hydrogen 

 blow-pipe. 



Volatility is the property which some metals exhibit of going 

 off in vapour at certain temperatures. Mercury, arsenic, tellu- 

 rium, zinc, cadmium, potassium, sodium, can all be distilled from 

 their compounds. 



Alloys. When metals enter into combination, " alloys " are 

 formed. The union is now generally considered to be 

 " chemical." The various alloys will bo treated of under their 

 metals. An " amalgam " is an alloy in which one of the metala 

 is mercury. 



The Appearance of Metals in the Earth's Crust. Gold, pla- 

 tinum, silver, mercury, and copper are found " native " that is, 

 in an uncombined form ; but tho last-named three ara also found 

 as ores. Next to silica, metallic oxides are most widely distri- 

 buted in nature. Lime is the oxide of calcium. The tint of the 

 sandstones is due to the oxide of iron. Tho granite rocks con- 

 tain many oxides, while the waters of the ocean are rendered 

 briny with their salts. But the metals which we require in 

 iargo quantities we seek from masses of their ores, which are 

 found in mineral veins. It often appears that the older rocks 

 have, in the convulsions of Nature, been rent into fissures. 

 When these openings have not been filled up from below 

 with molten basalt, trap, etc., thus forming dykes, they have 

 been filled up with metallic ores, which seem to have been 

 usually deposited from above. These constitute " lodes." The 

 lodes of a neighbourhood generally run in the same direction, 

 and, strange to say, if this direction be altered, the ore gene- 

 rally alters its character, and frequently its chemical constitu- 

 tion. This and other reasons have led to the belief that 

 electricity has been the chief agent in depositing metallic veins. 

 It sometimes happens, as in the case of the iron beds in our 

 own country, that the ore ia found in strata, occupying the 

 position of a layer of rock. 



DIVISIONS OP THE METALS. 



1. Metals of tlie Alkalies: 

 Potassium. | Sodium. | Lithium. 



2. Metals of the Alkaline Earths. 

 Barium. I Calcium. 



Strontium. Magnesium. 



3. Metals of the Earths. 



Aluminum. 

 Glucinum. 

 Zirconium. 

 Thorinum. 

 Yttrium. 



Erbium. 



Terbium. 



Cerium. 



Lanthanum. 



Didymium. 



4. The Metals Proper. 



The last division is subdivided into classes of metala which 

 exhibit certain similar features. 



