228 ELECTRO-PLATING AND GILDING IRON 



is therefore equivalent to the coils alone being rotated over a stationary ring-shaped 

 magnet. The effect of this is to produce currents in the two halves of each ring in op- 

 posite directions between its two neutral points. At these points, however, contacts 

 are placed, which touch in succession a series of studs connected, at regular intervals. 

 with the wire-coil. Thus the opposite currents in the two halves of each ring, instead 

 of neutralising each other, unite and form a single current. The machine requires a 

 very small amount of force to drive it much less than one horse-power being ample 

 and it produces a very intense and steady flow of light. With this apparatus some 

 interesting experiments have lately been made by Mr. Robert Sabine at the works of 

 Messrs. Whieldon and Cooko, in the Westminster -bridge Road, where the machines 

 are being manufactured. It was shown that the current is producible in large 

 quantities, at a much cheaper rate, and of greater constancy than by galvanic batteries. 

 A further superiority over the batteries was also demonstrated in the fact that tho 

 resistance remains the same no matter at what speed the machine is driven, within 

 reasonable limits. Therefore, by driving it at double speed twice as much electro- 

 motive force is obtained, which represents, therefore, more than twice as much current. 

 In the experiments the machine was driven at a speed of about 320 revolutions per 

 minute, and the first object of tho exhibitors was to show the power developed by the 

 system. In the next place a length of 10ft. of platinum- wire was made red-hot in a 

 few seconds. This experiment was afterwards repeated with a chain of about tho 

 same length and composed of alternate links, six inches long, of silver and platinum. 

 While the platinum rapidly became red-hot, and remained so, the silver never became 

 more than inconveniently heated. Tho light-producing power of the apparatus was 

 then exhibited from the rear portion of Messrs. Whieldon's works. The light was 

 produced in tho usual way from carbon points and condensed in a concave reflector, 

 which threw the rays down a by-street on to premises in tho York Road, a long dis- 

 tance off, and which were brilliantly lighted up. The light was very intense and 

 remarkably steady, and would doubtless have fallen brightly on the Thames Embank- 

 ment had not the rays been intercepted by tho York Road premises. After the light 

 had been exhibited for some time, the experimenters illustrated tho power of the cur- 

 rent to fuse metals. This was done in the interior of the building, and platinum, 

 aluminium, silver, magnesium, strontium, metallic sodium, and steel were successively 

 and successfully burnt, the spectrum of each being thrown on a screen. Tho invention 

 will undoubtedly prove of great importance, for use in lighthouses and for metallurgical 

 purposes, as well as on shipboard, owing to the portability of the apparatus, tho small 

 space it occupies, and the slight power required to drive it. It has already been in 

 use for some time past with tho best results at the electro-plating works of Messrs. 

 Christofle and Co., of Paris, and is at present under trial by the Postal Telegraph 

 Department. Messrs. Whieldon and Cooke have constructed a machine which has 

 been employed for exhibiting a light in the clock-tower of the Houses of Parliament 

 during the sittings of the House, so that the public had an opportunity of judging of its 

 merits. This application of the electric light has not at present (1874) been adopted, 

 why, we know not. M. Gramme certainly deserves credit for this most important 

 contribution to applied science, by means of which he has practically solved the problem 

 of the production of cheap dynamic electricity. 



ELECTRO-PLATING AND GII/BXNG- IRON. Professor Wood, of 

 Springfield, Massachusetts, in a paper, which he has communicated to tho ' Scientific ' 

 American,' recommends the following as useful recipes for the electro-metallurgist. 

 He says, ' I believe it is tho first time that a solution for plating direct on iron, steel, 

 or Britannia metal has been published. In most of the experiments I have used 

 Smco's battery; but for depositing brass I prefer a battery fitted up as Grove's, using 

 artificial graphite obtained from tho inside of broken coal-gas retorts in the place 

 of platinum. With one largo cell (the zinc cylinder being 8 by 3 inches, and excited 

 with a mixture of one part sulphuric acid and twelve- parts water, the graphite l>eing 

 excited with commercial nitric acid) I have plated six gross of polished iron buckles 

 pur hour with brass. I have also coated typo and stereotype -plates with brass, and 

 find it more durable than copper-facing. 



' To prepare Cyanide of tiilvcr. 1. Dissolve 1 oz. of puro silver in 2 oz. of nitric 

 acid and 2 oz. of hot water, after which add 1 quart of hot water. 2. Dissolve 

 5 oz. of tho cyanide of potassium in 1 quart of water. To tho first preparation add 

 by degrees a small portion of the second preparation, until tho whole of the silver is 

 precipitated, which maybe known by stirring tho mixture and allowing it to settle. 

 Then drop into the clear liquid a very small quantity of tho second preparation from 

 the end of a glass rod : if the clear liquid is rendered turbid, it is a proof that tho 

 whole of the silver is not separated ; if, on tho other hand, tho liquid is not alien -.1. it 

 is a proof that the silver is separated. The clear liquid is now to be poured off; and 

 tho precipitate, which is the cyanide of silver, washed at least four times in hot 



