Electricity.

Date:
[1829]
Catalogue details

Licence: Public Domain Mark

Credit: Electricity. Source: Wellcome Collection.

    40/150 (page 50)
    employed in exploding the wires mentioned, the length of each wire being ten inches : the coated surface was the same in all the experiments, viz. one of his batteries of fifteen jars, exposing seventeen feet of coated surface. The column marked A, shows the diameter of the wires in parts of an inch; B the number of grains with which the electrometer was loaded; and C the color of the oxide deposited on the receiver:— A. B. C. Lead wire . i • 90 . 20 . Light gray. Tin wire 1 m . 30 . Nearly white. Zinc wire .. i ■ 90 . 45 . Nearly white. Iron wire . 1 • TSS . 35 . Reddish brown. Copper wire 1 * l5[) . 35 . Purple brown. Platina wire • 150 . 35 . Black. Silver wire . 1 • 150 . 40 . Black. Gold wire - • 153 . 40 . Brownish purple 238. Mr. Singer was of opinion that the charges here given by Mr. Cuthbertson were rather high, and attended with considerable risk of fracture to the jars: he repeated the experi¬ ments with shorter lengths of wire, and of less diameter; and with more moderate charges obtained the following results :— A. B. c. Gold wire ISO 18 Purple and brown. Silver wire 1 IBS 18 Gray, brown, and green. Platina wire ISO 13 Gray and light brown. Copper wire 1 1B0 12 Green, yellow, and brown. Iron wire . TSS 12 Light brown. Tin wire 1 Iso 11 Yellow and gray. Zinc wire . 1 T80 17 Dark brown. iLead wire . 1 TOT 10 Brown and blue gray. Brass wire . l 130 12 Purple and brown. 239. In the above experiments Mr. Singer did not use the receiver ; the wires, which were five inches in length, were stretched parallel to the surface of a sheet of paper, and distant from it about one-eighth of an inch. Brass wire is sometimes decomposed by the electrical charge, in which case its component parts, copper and zinc, are separated from each other, and appear in their distinct metallic colors when the explo¬ sion is made over a piece of glass. Indeed the figures of all the oxides are most beautiful when impressed on glass, although their colors are certainly less permanent. 240. This most amazing power of the electric matter is not only adequate to the oxidation of metallic substances, but is yet more remarkable in restoring oxides, already formed, to their metallic, or original state, for which purpose a very simple process will be found sufficient. 241. Into a small glass tube introduce a little of the oxide of tin ; let it cover about half an inch of the lower internal surface. Place the tube thus prepared on the table of Henley’s discharger, and introduce the pointed wires at each end, that the oxide may form part of the circuit. Pass now several strong charges in suc¬ cession through the tube, taking care to replace the oxide in its proper situation, should it be dispersed. If the charges are strong, the tube will soon become stained with the tin revived from the oxide. 242. In the same way nther metallic oxides may be revived ; but if vermilion be employed, which consists of sulphur and mercury, the mer¬ cury will be separated with such ease as that the charge of a moderately sized jar will be found quite sufficient. Decomposition of Water by Electricity. 243. The decomposition of water by electri¬ city was first effected by Van Troostwyk and Deiman, assisted by Mr. Cuthbertson ; this they effected by means of a complicated apparatus, and a very tedious process. Their method of procedure was improved on by Dr. Pearson, and after him by Mr. Cuthbertson: but the most simple form of an apparatus for this purpose is that of Dr. Wollaston. This apparatus is thus constructed :—Two finely pointed wires of gold' or platina are inserted into capillary tubes ; each wire is thrust into the tube till it nearly reaches the end of it, and the glass is softened by heat until it adheres to the wire and covers its point. The glass is then carefully ground away, till the point of the wire can be seen by the help of a magnifying glass. One of these wires is made to communicate with the ground, or with the nega¬ tive conductor of the machine, and the other with an insulated ball placed near the positive conductor, the two points are placed near each other in a vessel of water; when a current of sparks is discharged through the wares, a series of minute bubbles of gas will rise from the points of the gold wires, and, when collected in an inverted receiver, will explode on the application of a lighted taper. Dr. Wollaston found by experiment, that a point ^ of an inch in dia¬ meter, decomposed the water when the spark which passed from the conductor to the insulated ball was J of an inch in length ; and that a point -jAqjj of an inch in diameter, produced the same effect when the sparks were only ^ of an inch in length, Hence the rapidity of the decom¬ position was in proportion to the limited size of the point of the wire. 244. Of the results obtained in some experi¬ ments made with this apparatus, Dr. Wollaston gives the following account. By transmitting a current of sparks by means of two gold points over the surface of a card a little moistened, and tinged with litmus, and placed between the points, a redness was perceived about the positive ware after a few turns of the machine. When the negative wire was placed upon the red spot it was quickly restored to its former color. Hence he infers that the effect of an acid is produced at the positive ware; and that this effect is counter¬ acted by reversing its electricity. 245. Dr. Wollaston next coated two wires- with sealing-wax, so that their ends only were exposed : these he inserted into a solution of copper, and found that, on transmitting a current of sparks between them, the negative wire was coated with copper: the electricity of the wire being reversed, the copper quickly disappeared 246. When it is wished to decompose oils, alcohol, ether, &c., a much more simple, and less expensive apparatus will be found to answer every purpose. This apparatus, which is repre¬ sented by fig. 8, consists of a glass tube having a platina wife projecting from the top inwards and reaching nearly to the lower end. The lower