152 



♦ KNOWLEDGE • 



[Aug. 22, 1884. 



observations of the heavens. Hitherto we have only con- 

 sidered the apparent motion of the sun during a single day, 

 and that of the stars during a single night. We have to 

 inquire whether there are any changes from day to day, and 

 if so, what their character may be. It is clear that until 

 we are certain what the aspect of the heavens by day or by 

 night would be in the place whence we are to start on our 

 excursions, we cannot rightly estimate the significance of 

 the appearances presented in other places. 



ELECTRO-PLATING. 



X. 



By W. Slingo. 



TO the amateur or student, one of the most interesting 

 branches of the electrolytic art is the deposition of a 

 metallic film upon the skeleton of a leaf or upon a mould 

 of one. At this point in this series of papers we ought 

 rather to confine ourselves to the preparation of a mould 

 and the deposition of copper upon it. For several reasons, 

 however, it will be found better to take up and finally deal 

 with the finer work that is involved in plating or typing 

 small and delicate objects, such as leaves, insects, and other 

 animal and vegetable matter. 



To take an electrotype copy of a symmetrical two-sided 

 animal, such as a herring or other fish, is not diflicult. A 

 rather stiff paste of plaster is prepared and poured on to a 

 piece of greasy paper, fastened on a flat board — a rim 

 being provided to prevent the plaster spreading. The fish, 

 having been oiled to prevent adhesion, is laid on the j)laster, 

 and then gently pressed in until the lower half is, as it 

 were, enveloped or hidden. The plaster is then allowed to 

 dry until it is well set, although not quite hard, when the 

 object is removed and the edges of the mould finished off 

 with the aid of a knife. Two or three small holes are made 

 in the level portion surrounding the figure. The mould is 

 then brushed over with soap and water, and the fish re- 

 placed in its former position. A thin plaster paste is 

 then prepared and poured over the fish and lower mould 

 rather quickly. When quite set and thoroughly hardened, 

 the two moulds, each representing one side of the fish, are 

 easily separated, after which they are placed in an oven to 

 dry. When dry they are treated in the ordinary way — 

 that is to say, they are first saturated with molten wax, 

 and the surfaces, so far as they present an image of the fish, 

 are plumbagoed and connected to the negative electrode of 

 the bath ; leading wires are used if the fish, or whatever 

 else the object may be, is thick, or, in other words, if the 

 copy is to be a work in high relief. It would be possible 

 to make arrangements for taking the copy in one piece, but 

 it is preferable to take it in two pieces, and then filing, 

 fitting, and soldering them together. 



When the object to be copied is under-cut, or of such a 

 shape as to render the use of plaster impossible — as in the 

 case of, say, a mouse, the elastic-mould process is, as a 

 practical necessity, resorted to. Of course, it would be 

 possible to use plaster moulds, if we divide the copy into 

 four instead of two pieces. 



Leaves may be very faithfully and beautifully copied. 

 To take the upper side, a plaster-of-paris paste is prepared, 

 on which the back of the leaf is laid and gently pressed. 

 Some little care is necessary here to ensure a good result. 

 Air-holes must be filled up and the plaster, if necessary, 

 helped into its place by means of a thin stick of wood. 

 When thoroughly set and hard, plumbago is brushed 

 over and melted wax is poured on until a layer of 

 sufficient thickness is deposited. When cold, the wax is 



separated, coated with plumbago, and placed in the bath ; a 

 good electrotyped copy of the leaf i-esults, if the work has 

 l)een performed with sufficient care. Other substances 

 than plaster may be used for imbedding purposes, such as 

 clay or fine sand. Where, however, a soft substance is em- 

 ployed, it is advisable to make the leaf rigid by coating the 

 back with a few layers of thin plaster, allowing each 

 layer to dry before the successive one is applied. Sub- 

 stances which require pressure cannot be used for moulds, 

 because the surface or shape of the object is liable to 

 damage. Gutta-percha is therefore inapplicable. 



The process for plating leaves, flowers, insects, &c., is an 

 interesting one. The object to be coated is first dipped 

 into a solution of phosphorus in bisulphide of carbon. A 

 silver solution consisting of 1 dwt. of nitrate of silver 

 dissolved in a pint of distilled water having been prepared, 

 the object is immersed in it and kept in until the phos- 

 phorus has caused an entire coating of silver to be deposited, 

 which will be evidenced by a uniform blackness. After 

 washing in clean water, the silvered object is immersed in 

 a solution of chloride of gold, again washed in clean water, 

 and then allowed to dry. When dry, it is placed in the 

 bath, and a thin copper deposit is taken. If bisulphide of 

 carbon is not available, a silver coating may be obtained by 

 dipping the object in the nitrate of silver solution, and 

 then suspending it under a glass jar or receiver, closed at 

 the top, in which a piece of phosphorus is being burned. 



Another method is to grind in a mortar to a fine powder 

 some nitrate of silver crystals, and shake up the powder 

 with alcohol in a flask placed in warm water. One hundred 

 parts of alcohol should take up about 2^ parts of the 

 nitrate. The object to be copper-plated is dipped in the 

 solution, while warm, for a moment, and on withdrawing 

 the alcohol is allowed to evaporate, the nitrate being left 

 on the object. It is then placed in a vessel containing 

 burning phosphorus, when the salt is reduced and the usual 

 conducting coating is provided. 



Skeletons of leaves may be treated in the same way as 

 insects or flowers, and beautiful results obtained. The 

 appearance may be further considerably improved by 

 depositing a gold or silver film over the one of copper, of 

 which, however, more anon. I must leave the amateur to 

 work out any special design he may have in view, derived 

 from combinations of leaves, skeletons, and insects, and I 

 fancy that with a little application he may produce, with 

 the aid of various metallic solutions, some remarkably 

 pretty and attractive results. 



It is, perhaps, worthy of mention, as an interesting fact 

 rather than as an experiment to be repeated, that E. T. 

 Noualhier and J. B. Prevost, in 1S57, introduced a plan to 

 " metallise soft surfaces," such as a human corpse. All the 

 apertures, mouth nostrils, ic, were stopped -n-ith modellers' 

 wax, and pulverised nitrate of silver was spread over the 

 body with a brush. It was then placed in the bath, and a 

 copper coating deposited, the " result being a metallic 

 mummy." 



The next subject to claim our attention will be the 

 deposition of copper upon the baser metals, glass, ic. 



The number of workmen employed in oar dockyards at home in- 

 creased from 1879 to 1S8-1 from'l6,381 to 18,8i9. The armoured 

 building had been advanced from 7,427 tons in 1879-80 to 12,614 

 tons, as proposed in the Estimates for 1884-85. The expenditure 

 on armoured building for 1883-84 and 1884-85 was actually doubled 

 as compared with 1879-80. For the protection of our vast com- 

 merce in every part of the globe we maintain a fleet in commission 

 with an aggregate displacement of 324,256 tons, as comjiared with 

 171,300 tons for the French. Our fleet in commission was more than 

 double the tonnage of the French, but our mercantile marine was 

 tenfold larger than theirs. 



