HEADINGS IN LATIN. 



face of the article by moons of an adhesive varnish ; but in the 

 ease of metallic article* the gold is precipitated by various means 

 ! surfaoei. 



method introduced by Mr. Elkington is simple. Dissolve 



1 part of aiii-ii- tri-chlorido, the common "chloride of gold," in a 



littl.- \\at.-r. A Id to it 20 parts of the bicarbonate of potash 



ulually. An equal portion of tho bicarbonate is disHolvod 



of wat.T. Tho two solutions are mixed together 



iiiul lii'ilnl for two hours. Tho articles to be gilded arc dipped 



fur an instant in a mixture of equal parts of sulphuric and nitric 



to free their surfaces from any trace of oxide. They are 



removed rapidly into water and washed, and then immersed 



in tho hot gilding solution. If the gold is required to appear 



dead, a little salt is added to the acids which remove tho oxide. 



* of silver or German silver may bo gilded in this bath by 



joiniug them to a zinc or copper wiro and immersing both. 



This process has its defect in tho fact that as soon as the 

 surface is coated with gold, which is very thin, tho deposition is 

 arrested. Hence electro-gilding has superseded it. 



In order to render gold sufficiently hard to withstand tho wear 

 and tear of use, it is always alloyed. The standard gold is 

 composed of 1 port of copper to 11 of gold. 



The oxides of gold are tho sub-oxide (Au,0) and auric oxide 

 (Au,0 s ), sometimes called auric acid. The former is precipitated 

 as a green powder when a dilute solution of potash is added to 

 a solution of tho chloride of gold. Tho latter falls as a brown 

 powder when magnesia ia added to a solution of the tcrchlorido 

 of gold. Sunlight will decompose this oxide into oxygen and 

 gold. When treated with ammonia, fulminating gold is formed. 



Tho chlorides of gold correspond with the oxides, being auric 

 chloride (AuCl) and terchloride (AuCl s ). 



Tho chloride is got by exposing tho terchloride to a tempera- 

 ture equal to tho fusing point of tin. Two atoms of chlorine 

 are thua liberated, and the terchlorido is reduced to a mono- 

 chloride. The preparation of the terchlorido has been indicated. 

 It is a deep-coloured, yellow crystalline powder. It is the most 

 important of tho auric salts, and is used in photography to im- 

 part to photographic prints their purple tone. 



PLATINUM. 



SYMBOL, Pt CoMunrnro WEIGHT, 197'4 SPECIFIC GRAVITY, 21-5. 



Like gold, platinum is always found in a native state. It is 

 frequently alloyed with gold and silver, and generally with the 

 five rare metals palladium, rhodium, osmium, ruthenium, and 

 indium. The mines of Mexico and Brazil produce the metal, but 

 it is chiefly obtained from the gravel deposits at the foot of the 

 Ural Mountains. 



On account of its great infusibility it is difficult to procure. 



The chemical method devised by Wollaston consisted in dis- 

 solving the metal by means of aqua regia. Tho platinum, mixed 

 with some little indium, is precipitated from the clear liquid by 

 means of sal-ammoniac, when it falls as a yellow insoluble 

 powder, whose composition is 2NH 4 Cl,PtCl 4 . By heating this the 

 chlorine and ammonia are expelled, and the platinum left behind 

 in a porous mass, which is spongy platinum. To get the metal 

 in a solid form, this porous mass is reduced to powder and washed. 

 Tho powder, which is of a dull grey colour, is now submitted in 

 a mould to hydraulic pressure, and it assumes the appearance of 

 a metallic bar. This bar is heated in a wind furnace, and forged 

 by hammering it npon its ends. Platinum possesses tho same 

 property as iron ; it can be welded ; that is, when hammered 

 at a high temperature, the particles of the metal unite into a 

 solid mass. 



Deville and Debray procured solid platinum by submitting the 

 grains of metal, previously purified by digesting in nitric acid, 

 to fusion in a lime crucible, in the flame of tho oxy-hydrogen 

 blow-pipe. 



Properties. Its specific gravity is very high, being only inferior 

 to that of iridium. It does not tarnish under any circumstances 

 when exposed to the air, and cannot be attacked by any simple 

 acid. Hence it is much used in the laboratory for crucibles. Aqua 

 regia, however, convertsitintoaohloride. Very large and expensive 

 crucibles some cost ^62,000 are used to carry tho condensation 

 of sulphuric acid through its hist stage. It possesses great 

 ductility, and expands less by heat than any other metal. It 

 has the peculiar power of condensing gases on its surface, and 

 when a jet of hydrogen is directed upon a piece of spongy 

 platinum it is ignited ; because the oxygen condensed in the 



pore* of tho platinum, being than in a more active condition, 

 combine* with the hydrogen, and the beat developed i sufficient 

 to ignite the gas. This property b advantageously used in the 

 Davy lamp. Above the wick is a coil of fine platinum wire, and 

 when by any aocident the flame in extinguished, the vapoon of 

 the hydro-carbon* rising from the wick combine with the 

 oxygen on the surface of tho platinum, and thai the wire ia 

 rendered red-hot, and tho lamp re-lighted. 



Platinum combines readily with other m <^ft]f r and phoephorui 

 at hi(?h temperatures. 



When fused with potash or soda, in contact with the air, it will 

 oxidise. There are two oxides, platinous oxide (PtO) and platinic 

 oxide (PtO,). They are procured by the precipitation of corre- 

 sponding salts by a regulated quantity of alkali. Both oxide* 

 are soluble in an excess of the alkali. 



There are sulphides of a like composition to the oxides. 



The chlorides are the most important salts. 



When the metal is dissolved in aqua regia a red solution is 

 obtained, which consists of a tetrachloride (PtCl 4 ), platinic 

 chloride. When evaporated to dryness a salt is procured, which 

 has two molecules of hydrochloric acid in it (PtClaH,) at 230 C. 

 This acid is given off, and also two atoms of chlorine, leaving 

 platinous chloride (PtCl,). At a still higher heat the metal is 

 reduced. 



Platinic chloride is of great service in analysis in determining 

 the quantity of potash or ammonia present in a solution. 



It forms with both these, sparingly, soluble salts. 



In the case of potash, when the salt is submitted to a red 

 heat, metallic platinum and potassium chloride are left; bat 

 with the ammonia salt nothing but the metal remains. The 

 action of ammonia on platinous chloride is remarkable. Many 

 salts are formed by an atom of platinum replacing some of the 

 hydrogen of the ammonia ; but these salts are of more interest 

 in a theoretical than a practical light. 



With platinic chloride any of the potassium salts give a yellow 

 precipitate ; but with sodium salts a brown hydrated oxide falls. 

 With ammonia salts the yellow precipitate above alluded 

 to appears, which on heating may be distinguished from the 

 potassium precipitate. By this means these three alkalies may 

 be recognised. Platinum Is not reduced from its solutions as 

 gold ia by ferrous sulphate or oxalic acid. 



The rarer metals associated with platinum do not require notice. 



READINGS IN LATIN. I. 



SELECTIONS FROM C.ESAB. 



THE student will now be anxious to read more lengthy extracts 

 of the Latin authors, of which he has at present only come 

 across separate sentences. The large number of these authors, 

 and tho great length of their writings, will prevent his gaining, 

 except at tho expenditure of a great deal of time and trouble, 

 anything like a general acquaintance with their style and cha- 

 racter ; and, accordingly, it is with this object that we propose 

 to give a series of extracts from those writers who are gene- 

 rally included in the course of study of this language. We shall 

 take the different authors one by one, giving a slight sketch of 

 the subject of their writings, and their special peculiarities of 

 diction, and adding extracts from them for the student to trans* 

 late. To each of the extracts will be appended short notes, 

 explanatory of such difficulties as the student will not be likely 

 to be able to solve merely by the aid of his Latin Dictionary 

 and the Latin Lessons ; while in each case a translation of one 

 at least of the passages selected will be given along with the 

 succeeding set of extracts, sometimes from original sources, 

 sometimes from published translations of acknowledged merit. 



It is to be observed that these readings may be made useful in 

 more ways than one for acquiring a knowledge of Latin. They 

 sluuld be first translated literally, and then rendered into idio- 

 matic English ; and this second translation should be retrans- 

 lated into Latin, and when it is done, compared with the original 

 We cannot impress too strongly npon the student the advan- 

 tages of this course of proceeding ; he will find that his mind 

 will gradually become stored with Latin phraseology, and his 

 own style of writing Latin composition will have the advan- 

 tage of being formed upon the best models. We should add 

 that this system is most readily applicable to the prose ex- 

 tracts, though it will be found of great service also in verse- 

 making. 



