chalk than Latin and Geeek, provided that we will observe the broad ground lines of the history it has to tell; and now, if you please, let us spell, in company this history. We know that if chalk is burnt, the result is quicklime. Chalk is a compound of carbonic acid gas and lime, and if it is much heated the carbonic acid evaporates, and the lime remains. By this experiment we see the lime, but we do not see the carbonic acid. But if you pulverize a little chalk, and pour the powder into strong vinegar, much bubbling and fizzing takes place, and finally a clear liquid is produced in which no more chalk is visible. There the carbonic acid in the little bubbles is seen; but the chalk which was dissolved in the vinegar disappears from sight. The chemists prove this kind of composition of the chalk still by other experiments which I here pass over, and they teach us that it almost entirely consists of carbonic acid and quicklime. It is useful to us to proceed from the knowledge of this fact though it seems of not much help. For the carbonic acid of the lime is a substance far spread which we encounter under very different conditions. All kinds of lime-stone are composed from more or less pure carbonic acid and lime. HOW IT APPEARS UNDER THE MICROSCOPE. If you grind a slice of chalk down so thin that you can see through it, it appears quite differently, when it is observed under the microscope. Generally, the mass consists of small granules; innumerable corpuscles are imbedded in this matrix, some smaller, some larger, but not longer than one-hundredth of an inch in diameter (having a well defined shape and structure.) A cubic inch of some species of chalk, may contain hundreds of thousands of these bodies compacted together with in |