336 



• KNOWLEDGE ♦ 



[Oct. 24, 1884. 



own. Yet, were the air of no colour, it is very certain 

 that through a great mist the light of a flambeau at some 

 distance appears reddish, tho' it be not its true natural 

 colour. Our air is nothing but a great mist, which changes 

 the true colour of the sky, sun, and stars ; it belongs only 

 to the celestial matter to bring us the light and colours as 

 they really are in all their purity ; so that, since the air of 

 the moon is of another nature than our air, or is diversiiied 

 by another colour, or at least is another kind of mist, which 

 varies the colours of the celestial bodies. In short, as to 

 the people of the moon, their spectacles thro' which they see 

 everything are changed." 



" If it be so," said the Marchioness, " I prefer this abode 

 before that of the moon, for I cannot believe the celestial 

 colours are so well suited as they are here. For instance, 

 if you put green stars on a red sky, they cannot be so 

 agreeable as stars of gold on an azure firmament." 



" To hear you, one would imagine, madam," said I, " you 

 were chusing a petticoat or a suit of knots ; but, believe 

 me, nature does not want fancy. Leave it to her to chuse 

 colours for the moon, and I '11 engage they shall be well 

 sorted. She will not fail to vary the prospect of the uni- 

 verse, at every different point of sight, and always the 

 alteration shall be very agreeable." 



"I know very well," said the 3Iarchioness, " her skill in 

 this point ; she is not at the charge of changing the objects, 

 but only the spectacles, and has the credit of this great 

 variety without being at any expense : with a blue air she 

 gives us a blue firmament ; and perhaps with a red air she 

 gives to the inhabitants of the moon a red firmament, and 

 yet still it is but the same firmament, nay, I am of opinion 

 she has plac'd a sort of spectacles in our imagination, thro' 

 which we see all things, and which to every particular man 

 change the objects. Alexander look'd on the earth as a 

 fit place to establish a great empire ; it seem'd to Celadon 

 a proper residence for Astrrea, and it appear'd to a philo- 

 sopher a great planet in the heavens cover'd with fools. I 

 do not believe the sights vary more between the earth and 

 the moon than they do between one man's fancy and 

 another's." 



" This change in our imaginations," says I, " is very sur- 

 prising; for they are still the same objects, tho' they 

 appear different; when in the moon, we may see other 

 objects we do not see here, or at least not see all there we 

 do see here. Perhaps in that country they know nothing 

 of the dawn and the twilight, before the sun rises and 

 after the sun sets : the air which encompasses, and is 

 elevated above us, receives the rays, so that they cannot 

 strike on the earth, and being gross, stops some of them, 

 and sends 'em to us, tho', indeed, they were never naturally 

 design'd us ; so that the daybreak and the twilight are a 

 favour which nature bestows on us : they are lights which 

 do not properly belong to us, and which she gives us over 

 and above our due. But in the moon, where apparently 

 the air is more pure, and therefore not so proper to send 

 down the beams it receives from the sun before his rising, 

 and after his setting, they have not that sight of grace (as 

 I may call it) which, growing stronger by degrees, does 

 more agreeably prepare them for the arrival of the sun ; 

 and which growing weaker, and diminishing by degrees, 

 does insensibly prepare them for the sun's departure : but 

 they are in a profouud darkness, where a curtain (as it 

 were) is drawn all on a sudden, their eyes are immediately 

 dazzled with the whole light of the sun in all its glory and 

 brightness ; so, likewise, they are on a sudden surprised 

 with utter darkness, the night and the day have no medium 

 between them, but they fall in a moment from one extreme 

 to the other. 



(To be continued.) 



ELECTROPLATING. 



By W. Slingo. 



XII.— SILVERING SOLUTIOXS. 



ONE cannot but be struck with the great beauty and 

 variety of the works of art observable in any good 

 electroplater's show-room. Nor can there be any doubt that 

 the discovery and pursuit of the art of depositing silver 

 electrically, has given a considerable impetus to the trade 

 in silvered goods. As an involved consequence of the 

 profit at first made, competition speedily Het in, the result 

 being a cheaper article with the maximum amount of 

 tasteful embellishment. At the present moment, the in- 

 dustry has developed into truly gigantic dimensions, tons 

 and tons of silver being utilised in th<> process. 



The beauty of the work produced lends naturally a great 

 charm to the process from an amateur's point of view. Nor 

 are the experiments accompanied by an undue amount of 

 trouble, while with the adoption of fitting precautions, 

 failure is an unlikely result. 



The first thing to be done in starting on a small scale is 

 to prepare the solution which is to be placed in the electro- 

 lytic bath. Of course, the expense is greater than that 

 involved in the deposition of copper, but it is not so great 

 as to present a serious obstacle even to one of very re- 

 stricted means. The chief outlay is at the beginning. A 

 solution once made should last a long time in use without 

 seriously deteriorating. The duration is practically governed 

 by the quality of the ^^ingredients. The silver which is 

 deposited on the plated article appears at the expense of 

 the silver plate used as the anode or positive electrode in 

 the bath, because, although the particles of metal cannot 

 be said to traverse the solution, there is, nevertheless, a 

 particle dissolved oft the plate for every particle that finds 

 its way from the solution on to the article forming the 

 cathode or negative electrode. 



The last few lines render it almost superfluous to say 

 that the silver employed should be of the finest. Impure 

 silver or alloys will not do, but if no other is available, a 

 purifying process must be resorted to. The simplest consists 

 in dissolving the impure metal in nitric acid, adding the 

 alloy grain by grain, until the whole is dissolved. Do not 

 use too much acid, but start first with a very small quan- 

 tity, and then, should it prove insufficient to dissolve all the 

 metal, add a little more. When the solution is completed, 

 add a little cold water, at the rate of half a pint to an 

 ounce of metal. Then drop in a few pieces of copper, 

 which the acid will take up, setting free the silver. 

 This silver is then jireeipitated in a pure state on the sur- 

 face of the copper, just as copper is precipitated on iron, 

 when a piece of that metal is immersed in a sulphate of 

 copper solution. The supernatant liquor which now con- 

 sists of nitrate of copper, instead of nitrate of silver, mixed 

 with nitrates of the various impurities, is next poured 

 off carefully, and the deposited silver well washed lu clean 

 water. 



Having procured the pure metal, dissolve, say an ounce 

 of it, little by little, in a mixture consisting of rather more 

 than an equal weight of good nitric acid (specific gravity 

 1-420) and about a quarter of an ounce of water. A "word 

 to the wise " is, however, necessary here. In the first 

 place, nitric acid is exceedingly corrosive. Coat sleeves 

 and trousers vanish beneath it in a sometimes alarming 

 fashion, and its effect upon a mahogany dining-room 

 table is anything but entertaining, except In the eyes 

 of a young " destroy - all." If it comes into con- 

 tact with the skin it destroj-s it, turning it a yellow 

 colour, which only disappears as the skin wears off. 



