CHEMISTRY. 



17 



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Elements 4.. The metals are not known to combine with 

 f simple incombustible!. But they combine with each 

 other, and form a set of important compounds, called 

 alloys. Thus brass is an alloy of copper and zinc ; 

 and bell metal an alloy of copper and tin. When 

 mercury is one of the metals combined, the com- 

 pound is not called an alloy, but an amalgam. Thus, 

 the amalgam of gold is gold dissolved in mercury. 



5. The metals at present known (excluding the 

 new ones discovered by Davy, which will be better 

 described afterwards) amount to 27. They may be 

 divided into the four following sets : 



List of 

 metali. 



Gold. 



1. Gold. 



2. Platinum. 



3. Silver. 



4. Mercury. 



5. Palladium. 



6. Rhodium. 



7. Iridium. 



I. Malleable. 



8. Osmium. 



9. Copper. 



10. Iron. 



11. Nickel. 



12. Tin. 



13. Lead. 

 11. Zinc. 



II. Brittle, and eatHy Fused. 



1. Bismuth. 3. Tellurium. . 



2. Antimony. 4. Arsenic. 



III. Brittle, and difficultly Fused. 



1. Cobalt. 4. Molybdenum. 



2. Manganese. 5. Uranium. 



3. Chromium. 6. Tungsten. 



IV. Refractory. 



1. Titanium. 3. Cerium. 



2. Columbium. 



The fourth set consists of metals which have not 

 hitherto been obtained in quantities, except in the 

 state of oxides. Formerly the brittle metals were 

 called KmimetaU, and the malleable, metals. The 

 first four malleable metals were once considered as 

 noble, because their oxides may be reduced by mere 

 heat. 



SECT. I. Of Gold. 



Gold seems to have been the first known of all the 

 metals. As it occurs always in the metallic state, 

 and is very soft and ductile, less skill would be ne- 

 cessary to work it. 



Properties. 1. Gold has a yellow colour, considerable lustre, 

 and is destitute of taste or smell. It is very soft. 

 Its specific gravity is 19.376, that of water being 

 1.000. It is the most ductile and malleable of all 

 known bodies. It may be beaten out into leaves 

 on ' v Tie'eaath P art f an ' ncn '" thickness, and 

 drawn out into wire extremely fine. Its tenacity is 

 considerable ; a gold wire, 0.078 inch in diameter, be- 

 ing capable of supporting 150.07 ibs. avoirdupois 

 without breaking. 



It melts at 32 Wedgewood, and, when melted, 

 has a bluish green colour. It does not sensibly waste 

 nor alter, though kept very long in the state of fu- 

 sion. In very violent heats, however, it hag been 

 rot. vi. PART i. 



perceived to be partially volatilized. When careful- Elements 

 ly cooled after fusion, it sometimes crystallizes in four- 

 sided pyramids. Gold is not altered by exposure to 

 the air ; it does not even lose its lustre. 



2. It combines with oxygen, and forms different Oxides, 

 oxides, the number and properties of which are but 

 imperfectly known. Two have been described. The 



first, or the purple, is formed when violent electri- 

 cal explosions are passed through gold leaf, or when, 

 gold is subjected to combustion. It is probably a 

 compound of 100 gold and 8 oxygen. 



The second, or peroxide, is of a yellow colour. 

 It may be obtained by dissolving gold in nitro-tnu- 

 riatic acid, and then precipitating the metal by means 

 of lime-water. It falls in the state of this yellow 

 oxide. When carefully washed and dried, it is inso- 

 luble in water, and tasteless. From an experiment 

 of Proust, we may infer, that it is composed of 100 

 gold and 32 oxygen. 



It combines with chlorine, and forms the yellow- 

 coloured, deliquescent, strong-tasted salt, at present 

 distinguished by the name of muriate of gold. 



3. Hitherto gold has been united with only one of 

 the simple combustibles, namely phosphorus. Hy- 

 drogen and charcoal are said to precipitate it from 

 its solutions in the metallic state. With sulphur it 

 does not combine. The action of boracium has not 

 been tried. 



The compound of phosphorus and gold is called Phosphu- 

 phosphuret of gold. It may be formed by dropping ret. 

 small pieces of phosphorus into gold in fusion. It is 

 brittle, whiter than gold, and contains -j^th of phos- 

 phorus. The phosphorus may be dissipated by ex- 

 posing the compound to a sufficient heat. 



4. As far as is known, gold does not combine with 

 azote. 



5. It combines readily with most of the metals, 

 and forms a variety of alloys. 



Gold is so soft, that it is seldom employed quite Alloys. 

 pure. It is almost always alloyed with a little cop. 

 per or silver. Goldsmiths usually announce the pu- 

 rity of gold in the following manner. Pure gold is 

 divided into 24 parts, called carats. Gold of 24 ca- 

 rats, means pure gold ; gold of 23 carats, means 23 

 parts of gold alloyed with 1 part of some other me- 

 tal ; gold of 22 carats, 22 parts of gold alloyed with 

 2 parts of some other metal. The number of carats 

 mentioned specifies the pure gold, and what that 

 number wants of 24 indicates the quantity of alloy. 

 The gold coin of this country, or Stirling gold, as 

 it is called, is gold of 22 carats. Jewellers' gold is 

 gold of 18 carats. 



SECT. II. Of Platinum. 



Platinum, which approaches to gold in many of its platinum. 

 properties, was unknown in Europe as a peculiar me- 

 tal till 1749. Hitherto it has been found only in 

 South America, in St Domingo, and in the silver 

 mine of Guadal canal iu Spain. For the first accu- 

 rate investigation of its properties, we are indebted 

 to Dr Lewis ; and since his time it has been investi- 

 gated by a great number of very eminent chemists. 



It is brought from America in small flat grains, 

 having a silvery lustre. These grains, besides plati 

 c 



