18 



CHEMISTRY. 



num, contain no less than eight other metals. The 

 platinum may ! obtained purr, by dissolving t'ie 

 BI in nitro muriatic acid, and pouring a solution 

 ' niiiiioniric into the liqu d. An orange yellow 

 precipit.i . This precipitate is to be washed 



and dried, and t-xpoM-d to a red heat. The pu 

 which remain* is pure platinum. It may be amalga- 

 mated with mercury ; and, by cautious heating and 

 hammering, it may be rcduci-d into an ingot. 



I'ropertit*. 1. Pl.ttinum has a white colour like silver, but not 

 to bright. It is ai hard as iron. I 1 9 specific gravi 

 ty. *'''' i hammered, is .it least 23, .->o that it is the 

 hc.ivK- t of nil known bodies. It in very ductile and 

 malleable. A platinum wire of the diameter 0.078 

 inch, H capable of supporting 27 -t.'Jl Ibs. avoirdupois 

 without breaking. It is very difficult ot fusion, and 

 ind- be melted in any quantity by the great- 



est heat can produce. But at a white heat, 



pieces of platinum may be welded together like pie 

 ces t" hct iron. It is not altered by the action of 

 heat wd air. 



Oxides. g. Flat mum cannot be converted into an oxide by 



the act'on iT heat jnd air; we must have recourse to 

 the action of acids. There are two oxides of plati- 

 num known: the protoxide is green, the peroxide 

 brown. 



The peroxide may be obtained by pouring lime 

 water into the solution of platinum in nitro muriatic 

 acid. The brown powder 'which precipitates is to 

 be dissolved in nitric acid, the solution evip.iratrd to 

 dryness, and the acid driven off by a cautious appli- 

 cation of heat. The brown powder which remains is 

 the peroxide. It is tasteless, insoluble in water, and 

 decomposed by a red heat. It is composed, accord- 

 ing to Mr Chenevix's experiments, of 

 87 platinum, 

 13 oxygen. 



100 



If the peroxide is gradually heated, it assumes a 

 green colour, owing to the separation of a quantity 

 of oxygen. This green powder is the protoxide, 

 composed cf 



93 platinum, 

 7 oxygen. 



100 



Chlorine combines with platinum, and forms the 

 dark brown substance distinguished by the name of 

 muriate of platinum. 



Phosphn- 3. The simple combustibles have but little action 

 ret " on platinum. Neither hydrogen nor carbon unites 



with it. Phosphorus combines readily, and forms a 

 phosphurel. It may be obtained by projecting phos- 

 phorus on red hot platinum. Its colour is silver white ; 

 it is very brittle and hard, and easily melts. The 

 phosphorus may be driven off by heat. Platinum 

 cannot be made to unite with sulphur. In this re- 

 spect it resembles gold. 



K .'.zotc does not combine with platinum. 

 Mloyi. ,. j t com t,j nea w i t j, m o;.t of the other metals, and 



forms allay!, first examined by Dr Lewis. 



Gold unites to it, but a strong heat is necessary to 

 combine them uniformly. Platinum alters the colour 

 of gold very much. An alloy of four parts of gold 



and one of platinum has the colour of pure platinum. Element* 



The .olour is much a'lected unless the platinum be 



less than T V'h i'f i'ie : J.I. ll fc uch au Ho) be di- -^^T 



gemed in nitric platinum is disM>lv<o. Thug 



it is ,-a-.y to iktcct a..y attempt to debase gold by the 



addition of platinum. 



SECT. 111. Of Silver. 



Silver seems to have been known almost as early as Silver, 

 gold. 



1. It has a fine white colour, with a shade of yel- Properties 

 low, and is remarkably brilliant when polished. It 



is rather harder th'i, ;;,)UI. Its specihY gravity is 

 about 10.510. In malleability and ductility, it ia in- 

 ferior to none of the metals except gold. It may be 

 hammered out into plates not more than , 00 ' flaa th of 

 an inch thick, and drawn out into wire finer than a 

 human hair. A silver wir;- 0.078 inch thick, is ca- 

 pable of supporting 187. 13 Ibs. avoirdupois, without 

 breaking. It melts when thoroughly red hot, or at 

 the temperature of '22 Wedgewood. By a very vio- 

 lent heat it may be boiled, and partly volatilized. 

 When cooled slowly, it crystallizes in four-sided py- 

 ramids. 



2. By very long exposure to heat and air, silver Oxides, 

 may be oxtdi/ed ; but the process is so tedious and 

 difficult, that we cannot have recourse to it. There 



are two oxides of silver known, both of which have an 

 olive green colour. 



The peroxide may be formed by dissolving silver in 

 nitric acid, and precipitating, by means of lime water. 

 The powder which falls, when washed and dried is 

 the peroxide. It is tasteless and insoluble i:i water. 

 When exposed to light or to heat, it is decomposed, 

 and the silver reduced. It is composed of about 

 92.67 silver, 

 7.33 oxygen. 



100 



The protoxide may be formed by heating the so- 

 lution of silver in nitric acid, in contact with a quan- 

 tity of granular silver. It resembles the peroxide in 

 colour, but its combination with nitric acid is more 

 soluble. 



Chlorine combines with silver, and forms with it 

 the white-coloured, insoluble, and tasteless substance, 

 at present distinguished by the name of muriate of 

 silver. 



3. Neither hydrogen nor carbon hare been combi- 

 ned with silver ; but it combines readily with sulphur 

 and phosphorus. 



When thin plates of silver and sulphur are laid al> Sulphurct. 

 ternately in a crucible, they melt by a moderate heat, 

 and form sulphuret of silver. This compound is found 

 in silver mines, or it exists native, as mineralogists 

 term it. It has a dark grey colour, a metallic lustre, 

 and the softness, flexibility, and malleability of It-ad. 

 Its specific gravity is 7.2. It is composed of 87.27 

 silver, and 12.73 sulphur. When silver plate is long 

 exposed, it contracts a thin covering of this substance. 

 Hence the tarnish of silver is owing to its combining 

 with sulphur. 



Phosphurct of silver may be formed by projecting l'I">sphi>- 

 phoephorus into melted silver. It is white, composed ret ' 



