CHEMISTRY. 



of 

 Chemistry. 



Oxide;. 



Phosphu- 

 ret. 



ing. It melts at 612*. When slowly cooled, it 

 crystallizes in 4 sided pyramids. 



2 Lead soon tarnishes in the open air, but the 

 oxidizemcnt never proceeds far. Water does not 

 act upon it, though it greatly facilitates the action 

 of the external air. Lead is believed at present to 

 be capable of forming 3 different oxides. 



The yellow oxide is the most important, as it con- 

 stitutes the basis of almost all the known salts of 

 lead. It may be obtained by dissolving lead in nitric 

 acid, precipitating by carbonate of potash, and heat- 

 ing the white powder which falls almost to redness. 

 It is yellow, tasteless, insoluble in water, but solu- 

 ble in potash and in acids. It readily melts, and 

 forms a brittle semitransparent hard glass. It is 

 composed of 100 lead and 7.7 oxygen, it may be 

 formed by exposing lead for a sufficient time to the 

 action of heat and air, and is then known by the 

 name of massicot. 



If yellow oxide be dissolved in nitric acid, and the 

 solution boiled over a quantity of lead filings in a 

 phial, the liquid assumes a yellow colour, and yields 

 yellow, brilliant crystals, in scales. These crystals, 

 according to Proust, consist of nitric acid united 

 to an oxide of lead, containing less oxygen than yel- 

 low oxide. But his experiments have not been veri- 

 fied by subsequent inquirers. 



If massicot, ground to a fine powder, be exposed 

 in a furnace to the flame of burning coals, playing 

 upon its surface for about 48 hours, it is converted 

 into a beautiful red powder, called minium, or red 

 lead. This is the deutoiide or red oxide of lead. It 

 is of an orange red colour, of the specific gravity of 

 8.94O ; insoluble in water, but soluble in potash. 

 AVhen heated to redness, it gives out oxygen gas, and 

 is partly reduced, and partly melted, to a dark brown 

 glass. It does not combine witli acids. When acids 

 dissolve it, they first reduce it \o the state of yellow 

 oxide. It is composed of 90 lead, and 10 oxygen. 



If weak nitric acid be poured upon red lead, a 

 portion is dissolved, but a portion remains in the state 

 of a dark bntiKii pointer. This brown powder is the 

 peroxide of lead. It is tasteless, light, and \t not 

 acted on by sulphuric or nitric acid. To muriatic 

 acid it gives out oxygen, and converts it into oxy- 

 muriatic acid. It is composed of 8G.5 lead, and 13,5 

 oxygen. 



When lead is firt extracted from its ore, it almost 

 always contains a portion of silver, which is always 

 extracted when its quantity is sufficient to repay the 

 expeuce. The process is known by the name of re- 

 fhii ig the lead. The lead is placed in a large flat 

 diOi, called a test, composed of burnt bones and fern 

 ashes, and exposed to the flame of a furnace. The 

 lead gradually assumes a kind ot vitriform state, and 

 is either blown off or sinks into the test, while the 

 silver remains unaltered. The lead by this process 

 is converted into litharge. It consists of fine scales, 

 partly red and partly yellow. It is yellow oxide, 

 combined with a small portion .( carbonic acid. 



3. Lead has not been combined with hydrogen or 

 carbon, but it unite-- to pbotpborus and sulphur. 



Phosphuret of lead may be formed by dropping 

 phosphorus into melted lead. It has a silver white 

 colour, wth a shade ot blue, and soon tarmthes. 



VOL. VI. PAHT I. 



Sulphuret of lead may be formed by mixing the Elements 



two ingredients and melting them in a crucible. It . . 



I,, - j , ,1 Caemistrv. 



occurs abundantly native, and is known by the name _^/^,_/ 



of galena. It is brittle, brilliant, of the colour of Sulpliuret. 

 lead, less fusible, and usually crystallizes in cubes. 

 Its sp-ocific gravity is about 7. It is composed of 

 Sb'.o lead and 13.5 sulphur. 



There is another sulphuret of lead, which has 

 been occasionally found native also. The colour is 

 lighter, and it burns with a blue flame when placed 

 upon burning coals. It contains at least 25 per cent, 

 of sulphur. 



4. Lead does not combine with the simple incom- 

 bustibles. It forms alloys with the other metals, but 

 few of them are of much importance. 



It renders gold as brittle as glass, when the pro- Alloyj. 

 portion of it does not exceed -r^rrsth f the g'd. 

 It likewise renders platinum brittle. The alloy of 

 silver and lead is very brittle ; its specific gravity ig 

 greater than the mean. Mercury readily dissolves 

 lead, and forms an amalgam capable of crystallizing, 

 Copper dissolves in lead at a strong red heat. The 

 alloy is grey and brittle, and when heated gradually, 

 the lead melts and runs off, leaving the copper nearly 

 pure. Iron unites with lead with difficulty, and the 

 alloy is easily decomposed. Lead and tin may be 

 combined in any proportion. The alloy is harder, 

 and possesses more tenacity than tin. 



SECT. XIV. Of Zinc. 



The ancients do not appear to have been acquaint- Zinc. 

 cd with this metal. It has been long known in Chi- 

 na, and is mentioned by European writers in the 13th 

 century. The method of extracting it from its ores 

 was unknown in Europe till near the middle of the 

 18th century. 



1. Zinc has a brilliant white colour, with a shade Properties, 

 of blue, and is composed of thin plates cohering to- 

 gether. It has a sensible taste, and acquires, when 

 rubbed, a slight smell. It is rather harder than sil- 

 ver. When hammered, its specific gravity is 7.1908. 



In its usual state it can scarcely be said to be mal- 

 leable ; but when heated a little above 2 1 2, it be- 

 comes very malleable, and may be rolled out into 

 thin plates, or drawn into wire. A zinc wire 

 0.078th inch in diameter, is capable of supporting 

 109.8 Ibs. When heated to about 680, it melts, 

 and, if cooled slowly, crystallizes in quadrangular 

 prisms. 



2. When exposed to the air, its surface is soon Oxides, 

 tarnished, but it hardly undergoes any other change. 



It is said to decompose water slowly, and to separate 

 the hydrogen. At a red heat, the decomposition 

 goes on rapidly. When zinc is heated to redness, it 

 takes fir.', and burns with great brilliancy, being 

 converted into a white oxide, which tt i'S ,-ft in fine 

 flakes like cotton. It was c.dled p"ij>holyj:, nihil al- 

 bum, lana. phi/OiOphica, jiumers of zinc. 



Only one oxide of zinc is known. It is the per- 

 oxide, or the white oxide obtained by the combus- 

 ti..n of the metal. It is composed of 80.39 parts 

 Z'nc and 19.61 oxygen. It may be obtained like- 

 wise by dissolving zinc in sulphuric acid, and preci- 

 pitating by means of potash. It is very white, light, 



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