Of what use are the two remaining substances, Hydrogen and Carbon?

These are appropriated by the vegetative organs to their growth and nourishment, while the oxygen with which the carbon was combined is abundantly given off to purify the air and render it fit for the respiration of animals.

Give me an idea of the mode in which Chemists ascertain the affinity of bodies, by relating an experiment.

Dissolve a tea-spoonful of sugar of lead in water, and pour the clear solution into a decanter or large glass bottle.  Then take a small piece of zinc, and twist round it some brass or copper wire, so as to let the ends of the wire depend from it in any agreeable form.  Suspend the zinc and wire in the solution which has been prepared; in a short time, metallic lead will deposit itself on the zinc and along the wire.  This is a beautiful illustration of chemical affinity; the acid, which constitutes a part of the sugar of lead, has a stronger affinity for the zinc than for the lead, and, consequently, will combine with the zinc, and form a compound which remains in solution, while the lead is precipitated on the zinc and wire in the form of a brilliant tree of metal.

     Affinity, in chemistry, that attraction which takes place
     between the elements of bodies, and forms compounds.

What does the word Nature signify?

In the above sense, the system of the universe; the creation, the works of God.  By the kingdom of nature is meant the world and all things in it:  nature is divided into three kingdoms, the animal, vegetable, and mineral.

What are the different states of natural bodies?

All bodies are either solid, liquid, or aeriform.  By solid bodies are meant those whose parts unite so firmly as to resist the impression or penetration of other bodies; by liquid, those substances whose parts do not unite firmly, but have free motion among themselves; by aeriform, fluid substances, having the form or nature of air.  Liquid substances are nothing more than solids converted into liquids by heat, a certain increase of which would convert the liquids into vapor.

What other name is given to Liquids?

They are likewise called fluids:  we call the air, also, a fluid, because it flows like a fluid, and light substances will float in it.

What is the cause of bodies floating on liquids?

It is an established law of nature, that all substances which weigh less than an equal bulk of any liquid, will float on the surface of this liquid.  Thus a cork will float on water, while a stone sinks to the bottom.  The cork will not float in the air, though lighter than water; and the stone is not heavier than the whole of the water, but more so than a portion of water of its own bulk,—­and thus it sinks in it.  Stones also differ in their weight or gravity:  for instance, some of the asbestus kind are lighter than water.  Iron, brass, indeed, nearly all substances, except gold and platina, will float upon mercury, because they are lighter than this liquid.