Charles. I perceive the same kind of taste which James described. How do you explain the fact?

Tutor. Some philosophers maintain that the principle of Galvanism and electricity is the same: and that the former is the evolution or emission of the electric fluid from conducting bodies, disengaged by a chemical process; while the latter is the same thing made apparent to the senses by nonconducting bodies.

James. All metals, as we have seen, are conducting substances; of course, the zinc,the guinea, and the half-crown, are conductors.

Tutor. Yes, and so are the tongue and the

saliva; and it is probable, that by the decomposition of some small particles of the saliva the sharp taste is excited.

Charles. What do you mean by the decomposition of the saliva?

Tutor. We shall, in our chemistry, show you that water is capable of being decomposed, that is, separated into two gasses, called hydrogen and oxygen.

James. Is saliva capable of being thus separated?

Tutor. Certainly, because a great part of it may be supposed to be water; and the oxygen combines with the metal, while the hydrogen escapes, and excites the taste on the tongue.

Charles. The disagreeable taste on the tongue cannot be disputed, but there is no apparent change on the zinc or the halfcrown, which there ought to be if a new substance, as the oxygen, has entered into the combination.

Tutor. The change is, perhaps, too small to be perceived in this experiment: but in others on a larger scale, it will be very evident to the sight, by the oxidation of the metals. James. Here is another strange word. I do not know what is meant by oxidation.

Tutor. The iron bars fixed before the window were clean and almost bright when placed there last summer.

James. But not being painted, they are become quite rusty.

Tutor. Now, in chemical language, the

iron is said to be oxidated instead of rusty; and the earthy substance that may be scraped from them, used to be called the calx of iron; but it is, by modern chemistry, denominated the oxide of iron.

When mercury loses its fine brightness by being long exposed to the air, the dulness is occasioned by oxidation, that is, the same effect is produced by the air on the mercury, as it was on the iron. I will give you another instance. I will melt some lead in this ladle, you see a scum is speedily formed. I take it away, and another will arise, and so perpetually till the whole lead is thus transformed into an apparently different substance: this is called the oxide of lead.

CONVERSATION XLV.

Galvanic Light and Shocks.

CHARLES. We had a taste of the Gal vanic fluid yesterday, is there no way of seeing it?

Tutor. Put this piece of zinc between the upper lip and the gums, as high as you can, and then lay a half-crown, or guinea, upon the tongue, and when so situated bring the metals into contact.

Charles. I thought I saw a faint flash of light.

Tutor. I dare say you did, it was for

that purpose I bade you make the experiment. It may be done in another way; by putting a piece of silver up one of the nostrils, and the zinc on the upper part of the tongue, and then bringing the metals in contact, the same effect will be produced.

James. By continuing the contact of the two metels, the appearance of light does not remain.

Tutor. No, it is visible only at the moment of making the contact. You may, if you make the experiment with great attention, put a small slip of tin foil over the ball of one eye, and hold a tea-spoon in your mouth, and then upon the communication between the spoon and the tin a faint light will be visible. These experiments are best performed in the dark.

Charles. Is there no means of making experiments on a larger scale?

Tutor. Yes, we have Galvanic, or, as they ought to be denominated, Voltaic,

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