M1STKY. 



[PLATI.XA AND GOLD. 



oeond das* wo have potassium and sodium ; and i 

 third, or those which M oxide* produce the earths, wo 

 have barium, strontium, A-c. Amongst these wo shall 

 licon, or silicium, which, although nut properly 

 al, will be more conveniently oousidurvd with thu 

 earths than apart by itself. 



With respect to the oxides of metals, we mar mention, 

 that although, pmpwly speaking, all the oxides may be 

 consider*! to be earths, the Utter term is confined to 

 Utose oxides which produce the constituents of rocks, A-c. , 

 in reference to mineralogies! and geologiosi doctrines. 

 Thus, oxide of iron is a component part of nearly every 

 earth, ret it is not reckoned of itself to be an earth. 

 Such distinctions may bo considered to be unnecessary, 

 but yet they are required in the present state of scientific 

 arrangement ; because although we may properly ht>i>u 

 for an extension of our knowledge in reference to the 

 constitution of clcmeuUry bodioft, we are compelled to 

 follow the analogies which existing facts point out The 

 oxide of barium, or of calcium, is perfectly analogous to 

 that of line or silver ; yet we designate the latter as 

 ores, whilst the two former are termed earths. Hence 

 arises what we may term a conventionalism of science, in 

 which it* principles are recognised, but not absolutely 

 insisted on. We admit the general laws, but also make 

 exceptions as to their details. lu this consists the 

 humility of philosophy ; for we must admit our ignorance, 

 whilst we use the facts of which wo are possessed. In 

 the words of Newton, we pick up one pebble, whilst we 

 reject that we previously gained, leaving the ocean of 

 truth (till unexplored before us. In the following pages 

 we shall first treat on what are termed metals proper ; 

 we shall then describe those which by oxidation produce 

 what are termed alkalies ; and, lastly, we shall deal 

 with the metals which, in combination with oxygen, 

 afford us the well-known substances called earths, in- 

 I'.udmg, as we have already stated, the substance colled 

 silicon, and its oxide, silica, or Hint 



PLATINA. 



iiany works on chemical and metallurgical science, 

 the term " noble" is applied to platitia, gold, and silver, 

 fr. m the fact that they are almost unalterable l>y any of 

 the numerous' agents which readily affect the appearances 

 of other metals. Platina eminently sustains tlu's cha- 

 racter, inasmuch as it withstands the agency of h. it. 

 being nearly infusible; and none of the acids affect it, 

 except aqua regia, which is employed as a solvent for it. 

 Platina is, comparatively speaking, a rare metal, and is 

 generally foiuul in thu form of small grains ; and iu this 

 state occasionally con tains iriiliiim, minium, A-c. It is 

 obtained pure by dissolving the native metal iu aqua 

 regia, and afterwards it is precipitated as a yellow powder, 

 by means of chloride of potassium. It La then heated with 

 carbonate of potash ; the mass so obtained being again 

 dissolved by means of aqua regia ; and the platiua is 

 then thrown down by a solution of sal-ammoniac, which 

 affords what is termed spongy pLitina, after Ixjing strongly 

 heated. Tho powder is made into ingots, by being 

 rammed into iron moulds, and heated in a wind- 

 furnace. This process aj^hitinntos the mass, which, 

 rhen cool, is hammered. Plutina has the property of 

 welding at a white beat, like iron; and it may afterwards 

 be rolled out into sheets, foil, ic., or drawn out into 

 wire. 



It resist* the action of the most intense heat of our 

 furnaces, being only melted by the oxy-hydrogon blo.v- 

 r by means of voltaic electricity. It has a colour 

 somewhat resembling, but darker than, silver, and is sus- 

 ceptible of a high polish, which it long i \\ hen 

 obtained in a spongy state, as already mention. .1, it has 

 the power of igniting a mixture of 

 gro gases, causing their combination*. For this purpose 

 platina is used in the Doln reim-r lamp, ami occasionally 

 in the laboratory. Employed in n similar manner w itii 

 alcohol, it maintains a slow cotnhiiHtion, which results in 

 JsW *0*i version of the spirit into acetic acid : even in the 

 of wire it may be made to maintain couibudion 



without the aid of a wick ; and is so used iu lamp 

 strut-tod to dill'iiKo porfumos in an apartment. A piece 

 of platina foil, twisted in , 



the manner shown in the 

 annexed engraving, and 

 surrounding the wick of 

 the spirit-lump, will con- 

 tinue red-hot, if tl' wick 

 l.o first ignited, and then 

 gently extinguished by 

 Mowing on it. 



The chemical symbol 



of platina is Pt ; "its equivalent 987; and its specific 

 gravity varies from 21 to -J2 ; that of water being 1. 



In this country the uses of platina are almost exclusively 

 confined to chemical vessels for laboratory purposes, and 

 for the distillation of sulphuric acid, lu Russia it is 

 used as coin ; and occasionally it is fashioned into snuff- 

 boxes, <kc. Spread in a state of fine powder on silver 

 plate, it forms the negative plate of the Since voltaic 

 battery. Its solution in aqua regia is also employed by 

 workers in silver, <tc., to produce a dark bronze-like 

 appearance. From the difficulty with which it is acted 

 on by chemical agents, its combinations are not so 

 numerous as those of some other metals. It combines 

 with oxygen to form an oxide and binoxide. Tho pro- 

 toxide is produced when a solution of potass is atMcd 

 to one of the bicliloride of platiua, and is a black powder, 

 which is readily decomposed by heat. The biuoxide is 

 similarly produced from the bichloride. 



The chief combinations of platina are the two chlor le.s. 

 The bicliloride is obtained by dissolving the pure metal 

 in nitro-hydrochloricacid, when a deep yellow ororange- 

 coloured liquid is produced ; aud the chloride may Lie 

 obtained from this by heatiug the bichloride to a tem- 

 perature of about 400 Fall. These two chlorides are 

 readily distinguishable ; the bichloride affording a yellow- 

 coloured solution in water, whilst the chloride is in- 

 soluble. With ammonia, the bichloride of platina ull'ords 

 a double salt, which is obtained by the addition of a 

 solution of sal-ammoniac to that of the metallic salt. 

 This double salt is often produced in the course of 

 organic analysis, aud affords a ready means of estimai in.; 

 the amount of nitrogen present in the Bobatanoa under- 

 going examination. For this purpose the ammonia is 

 converted, by means of hydrochloric acid, into the hydro- 

 chlorate, which is subsequently precipitated, by means of 

 the chloride of platiua, as a yellow-coloured powder ; and 

 the constitution of the salt so produced, K.i\ cs the cal- 

 culation of the ammonia an easy matter. 



GOLD. 



Tins metal is so well known, and so extensively em- 

 ployed for numerous purposes, that it requires but little 

 description. It has a specific gravity of about I'. 1 

 its symbol is An; ami its equivalent is 197. Like 

 platina, gold undergoes no change with the most in! 

 heat of our furnaces; it is simply melted, being quite 

 unvolatilisable. 



Although so precious a metal, it is widely diffused 

 throughout nature, and is discovered in those rocks of 

 which the mineral quartz is a component part. It is 

 also found in grains or nuggets, of sixes varying from a 

 grain to some hundred ounces in weight, in the beds of 

 many rivers. 



ierally speaking, it may be expected in any place 

 where the primitive rocks abound, and in the granite, 

 and allied formations ; it has been discovered in many 

 parts of Scotland, amongst which wo may mention the 

 Isle of Amin. In the south-west of Kn^land, as in 

 Cornwall, gold has often been mot with; but KO faros 

 our experience goes, at the present time there is no 

 source in Creat Britain which would repay the expense 

 of obtaining the 



In Russia, Germany, Africa, and Peru, gold mines 

 are worked to a profit ; but we need scarcely state, that 

 ilia and California are the chief place., from which 

 Kuropo obtains a supply of the metal. 



