286 



ELECTRICITY. 



point between the bell to be signalled at the 

 distant post and the earth connection, so that it 

 is only necessary to place the line wire in con- 

 tact with the earth a simple arrangement 

 that does away with what is ordinarily termed 

 a "switch," and requires personal attention 

 only periodically. The action of this alarm is 

 purely automatic. 



The same firm manufacture Crossley's Elec- 

 tric Engine Recorder or Indicator. In this 

 case the ordinary engine-counter is placed at 

 any distance desired, instead of being worked 

 by the engine direct. A simple contactor, 

 which may be worked by the beam or shaft 

 of the engine, causes a current of electricity 

 to pass along the wire connecting with the 

 distant end. Then it passes through two coils 

 of wire surrounding soft iron cores, and these 

 attract an armature as each current travels, 

 the armature working a lever as in the Morse 

 printing-telegraph. The indications are then 

 made with as much regularity as if the re- 

 corder were in the engine-house, instead of 

 being, as it may be, miles away. 



Nickel-plating by Electrolysis. A process 

 of nickel-plating, which is said to combine 

 cheapness with excellence, has been invented 

 by Prof. F. Stolba. The salt which he uses 

 may be the chloride or sulphate of nickel or 

 double sulphate of nickel and potassium. It 

 need not be chemically pure, but must contain 

 no metals which are precipitated by zinc. In 

 addition a solution of chloride of zinc is re- 

 quired, which may be obtained by dissolving 

 commercial zinc in common chlorhydric acid. 

 The process of plating may be effected in a 

 vessel of porcelain or metal ; the author pre- 

 fers copper, which itself becomes plated with 

 nickel. The articles to be plated may be of 

 cast or wrought iron, steel, copper, brass, zinc, 

 or lead. They must be completely immersed 

 in the liquid used for plating, and their surfaces 

 must be perfectly free from fat and rust. Iron 

 vessels may be cleaned by treating with a solu- 

 tion containing three or four per cent.of chlorhy- 

 dric acid. A sufficient quantity of a concentrated 

 solution of chloride of zinc is now poured into 

 the plating vessel, and from once to twice its 

 volume of water added. The solution is then 

 to be heated to the boiling-point, and chlorhy- 

 dric acid added drop by drop until the precip- 

 itate, formed by diluting the chloride of zinc 

 with water, is redissolved. As much zinc- 

 powder as will cover the point of a knife is 

 then added, by which the metal of the vessel 

 becomes, in a few minutes, plated with zinc 

 wherever it is in contact with this liquid. 

 Enough nickel-salt is then to be introduced to 

 color the liquid distinctly green, after which 

 the articles to be plated, and with them some 

 email cuttings of zinc, are to be put in, care 

 being taken to afford a sufficient number of 

 points of contact. The liquid is then to be 

 boiled, when the nickel is soon precipitated, and 

 the work is finished in about fifteen minutes. 

 If particular parts of the articles are not plated, 



the boiling must be continued, fresh pieces 

 of zinc, and, if necessary, fresh nickel-salt, be- 

 ing added. It is important, if the coating of 

 nickel is to be brilliant, that the liquid on boil- 

 ing shall not be cloudy from basic zinc salt, or 

 acid from free chlorhydric acid. The nickel- 

 plated articles must be well washed with water 

 and then cleaned with polishing-chalk. The 

 author found that articles of copper, plated 

 with nickel, after several mouths' exposure to 

 the atmosphere of the laboratory, appeared 

 scarcely tarnished. It is important to remark 

 that the same liquid may be employed repeat- 

 edly for nickel-plating, especially when chlo- 

 ride of nickel is employed. The same process 

 applies to cobalt, but the coating with this 

 metal, besides its cost, possesses no practical 

 value. 



Cold Galvanization of Iron. The metal is 

 first cleaned by being placed in a bath made 

 up of water 1,000 litres, hydrochloric acid 550 

 litres, sulphuric acid 50 litres, glycerine 20 li- 

 tres. On being removed from that bath, the 

 metal is placed in a bath containing 10 per 

 cent, of carbonate of potash, and is next trans- 

 ferred to a metallizing bath, consisting of wa- 

 ter, 1,000 litres ; chloride of tin, 5 kilogr. ; acid 

 sulphate of alumina, 4 kilogr. ; chloride of alu- 

 minium, 10 kilogr. The metal is left in this 

 mixture for from three to twelve hours, accord- 

 ing to the thickness of the layer of zinc to be 

 desired. 



Electrical Properties of Aluminium and 

 Magnesium. Mr. H. Highton communicates 

 to the London Chemical News the following 

 record of his experiments on this subject: 



As a positive, I find aluminium about equal to 

 iron ; and as a negative, inferior, if the iron be skil- 

 fully used. For, if iron be skilfully used, it is nearly 

 equal to copper ; used as a negative it should always 

 be in sucli a way as to form a black oxide on the sur- 

 face. I have lately been trying experiments with 

 magnesium as a positive ; the great evil of it is the 

 rapid local action which takes place, which, however, 

 by a peculiar arrangement, I have succeeded in en- 

 tirely overcoming. On the galvanometer I used, 

 which presented considerable resistance, an ordinary 

 Daniell's battery stood at 38. With magnesium for 

 the positive, and copper and sulphate of copper for 

 the negative, the current rose to 55. With magne- 

 sium as positive, and zinc for negative, I got a cur- 

 rent of 35 ; with iron for negative, 45 ; the first be- 

 ing nearly equal to Darnell's battery, and the latter 

 superior. With a different electrolyte, 1 got between 

 zinc and copper, 46 ; and magnesium and copper, 

 60. With another specimen of magnesium, pro- 

 cured fresh, the current rose to 67. I then took an- 

 other galvanometer showing smaller numbers, with 

 the following results : 



Zinc and copper, in an arrangement of my own 15* 



Magnesium and copper 26 



One of Grove's cells 22 



Oiie of Bunsen's cells 2(1 



Magnesium, with carbon and nitric acid for negative. .30' 



With platinum and nitric acid 29* 



Magnesium witb bichromate of potass and carbon for 

 negative 30* 



Thus, magnesium with platinum and carbon is to 

 zinc as about the tangents of 29 and 30 2 respectively, 

 to tangents of 22 and 26 ; but, with iron and cop- 

 per for negatives, it is to zinc nearly as 7 to 4. I 

 think 22 for Grove's cell was rather too low, as the 



