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10. If a round piece of zinc be laid on a piece of copper, each about two inches in diameter, and then a similar piece of flannel moistened with a solution of salt in water, and on these other layers in the same order, and so repeated several times, the whole will form a Galvanic pile, with which such experiments as the following are made. See fig. 2, p. 312.

EXPERIMENTS.

(1.) If the circle be completed by bringing one hand to the zinc at bottom, and the other to the copper of the upper layer, an electric shock will be felt.

(2.) If the circle be completed by a wire attached to the lowest plate of zinc and carried from thence to the upper copper, sparks will be given out.

(3.) By the same mode, if the pile be sufficiently powerful, very fine wire will be made red-hot, or even fused, so will gold leaf.

(4.) Electric batteries have been charged with the galvanic pile; and mixtures of oxygen and hydrogen gases may be exploded by it.

11. From these, and other experiments of the same nature, it has been inferred that the electric and galvanic fluids are the same.

12. Sometimes silver is used instead of copper: and it is ascertained that the zinc end of the pile is always positive, and the silver and copper always negative.

13. The zinc end of the pile is supposed to give out the electric fluid, which enters at the silver or copper end.

14. It is proved that chemical action is essential in Galvanism from this, that the action of the pile is most powerful in oxygen gas, and it ceases in a vacuum or in azotic gas.

15. It is supposed that all chemical action depends on the different states of bodies, that is, as to their being either in a positive or negative electrical state.

ILLUSTRATION.-All acids are naturally negative, and alkalies are positive, hence their speedy union. The results are neutral salts, which are found to be neither positive or negative

Experiment. If a neutral salt, as sulphate of soda, be

brought within the circuit of a galvanic pile, by means of wires extending to it from the zinc and copper, it will be decomposed; the acid, which is naturally negative, will be found at the positive or zinc end of the wire, and the alkali at the negative or copper end of the wire.

QUESTIONS FOR EXAMINATION.

1. What is Galvanism?

2. What is the difference of excitation in electricity and Galvanism?

3. What were Galvani's first discoveries?

4. What were his next observations?

5. With what is the diversity of metals, used in Galvanic experiments, connected?

Mention the experiments.

6. To what are the electrical phenomena exhibited by Galvanism to be ascribed?

7. How are the conductors in Galvanism distinguished?

8. Which are the perfect and imperfect conductors?

9. Of what must a galvanic combination consist?

Give the illustration.

10. Describe a galvanic pile:

Mention the experiments.

11. What is the inference drawn from these experiments? 12. Which end of the pile is positive, and which is negative? 13. Which is supposed to give out, and which to receive, the electric fluid?

14. What proof is there that chemical action is essential in Galvanism?

15. Upon what does chemical action depend? Give the illustration and experiment.

LESSON THE SECOND.

BATTERIES.

1. The pile, already described, was invented by Volta, who is justly regarded as the founder of the science, from the importance of his earliest discoveries; and on that account it is often, and will, probably hereafter, generally be denominated "Voltaism."

2. Another kind of Voltaic battery consists of a row of glasses or china cups, fig. 3, p.312, containing a solution of

salt and water; into one of the glasses, on the outer side, is put a plate of zinc fastened to a piece of wire made to bend over into the other cup, and to the other end is put a plate of silver: this is to be repeated with respect to all the glasses, so that each one will contain a plate of zinc and a plate of silver united with wire, except the outer glasses, in one of which will be a plate of zinc and in the other a plate of silver.

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Explanation. Fig. 2 represents a galvanic or voltaic pile, and fig. 3 a voltaic battery with glasses. In the former the letters Z CW are supposed to stand against the plates of zinc, copper, and moistened flannel; if a wire be placed at the lower, C, and another at the upper, Z, and brought together, the galvanic circle is complete.

In fig. 3, the letters z and s represent the plates of zinc and silver connected by wires w. By dipping one end in the glass z, and at the same time the other in the glass s, the circle is complete, and a galvanic shock is felt. Any number of glasses may be used, and the greater the number the more intense the shock.

Fig. 3.

Experiment.-By means S of the pile, fig. 2, water is decomposed: when silver is used instead of copper, and brass wires brought from the upper and lower

plates to a drop of water, hydrogen gas was evolved at the silver end, and the other wire was oxydated by uniting with the oxygen.

B

H

Fig. 4.

3. A battery of a more convenient kind consists of a trough, A B, fig. 4, made of baked wood, it is about three or four inches deep and as many wide. In the

sides are grooves opposite each other; into each pair of grooves is fixed by cement a plate of copper and a plate of zinc. The cells are then filled with a solution of salt and water, or what is still better, with a solution of nitrous or muriatic acid and water. The edges of the trough and plates are to be wiped very dry, so that there be no communication between the separate cells by moisture; and the trough is then fitted for experiments.

EXPERIMENTS.

i (1.) If one hand be put in the trough at A, and the other

at B, a severe shock will be felt.

(2.) If several persons join hands, with their hands previously moistened, and the two outer persons put their hand into the troughs as before, they will all feel a shock.

(3.) If new wires be attached to the two outer cells, the one to the zinc end, plate Z, and the other to the copper end, plate C, and by means of two small pieces of glass tube, E and F, the wire be brought into contact, a vivid spark will be given out; and if between them, on the glass pane G H, gunpowder, or charcoal, or gold-leaf, &c. be placed, they will be instantly inflamed.

Copper or brass leaf, commonly called Dutch gold, burns with a beautiful green light; silver leaf with a pale blue light; and gold leaf with a yellow light.

4. Several of these batteries may be united by iron cramps so as to act as one: the troughs are now constructed of the Wedgewood ware, and the plates made to move up and down for the convenience of experi

ments.

5. By means of these batteries the alkalies, some of the earths, sulphur, and other bodies, have been decomposed, which were, till lately, considered as simple bodies.

6. The limbs of people under amputation are sometimes convulsed by the application of the instruments, which is an effect of Galvanism.

7. Pure mercury retains its splendour a considerable time, but the amalgam of mercury with tin, or any other metal, soon becomes tarnished or oxydated, which is imputable to the galvanic action of the two metals.

8. Metallic works, the parts of which are soldered

together with other metals, soon oxydate about the parts where the different metals are joined, which is an effect of Galvanism.

9. In the sheathing of ships with copper where iron nails are used, the copper about the nails is quickly corroded.

10. Zinc may be kept in water a long time without much oxydation; but the oxydation goes on rapidly when there is silver or copper in contact with it.

QUESTIONS FOR EXAMINATION.

1. By whom was the pile invented, and on what account is this science called Voltaism?

2. Describe the battery made with glasses.

Give the explanation of the pile and glasses by means of the figures.

Explain how water may be decomposed.

3. What is the construction of the galvanic trough?

Give an account of the experiment.

4. How are several troughs made to act as one, and with what substance are these troughs made?

5. What effects have been produced by these batteries?

6. To what have the convulsive spasms experienced in surgical operations been ascribed?

7. Explain why amalgams soon become tarnished?

8. What parts of metallic works, in which different metals are used, are the soonest oxydated?

9. Where does the sheathing of ships soonest corrode?

10. In what manner may zinc be kept under water without corroding, and how will it rapidly corrode?

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