56 SELECTIONS FROM HUXLEY 



and lime, and when you make it very hot the carbonic acid 

 flies away and the lime is left. 



By this method of procedure we see the lime, but we do 

 not see the carbonic acid. If, on the other hand, you were to 

 5 powder a little chalk and drop it into a good deal of strong 

 vinegar, there would be a great bubbling and fizzing, and, 

 finally, a clear liquid, in which no sign of chalk would appear. 

 Here you see the carbonic acid in the bubbles; the lime, 

 dissolved in the vinegar, vanishes from sight. There are a 



10 great many other ways of showing that chalk is essentially 

 nothing but carbonic acid and quicklime. Chemists enun- 

 ciate the result of all the experiments which prove this, by 

 stating that chalk is almost wholly composed of "carbonate 

 of lime." 



15 It is desirable for us to start from the knowledge of this 

 fact, though it may not seem to help us very far towards 

 what we seek. For carbonate of lime is a widely spread sub- 

 stance, and is met with under very various conditions. All 

 sorts of limestones are composed of more or less pure carbon- 



20 ate of lime. The crust which is often deposited by waters 

 which have drained through limestone rocks, in the form of 

 what are called stalagmites and stalactites, is carbonate of lime. 

 Or, to take a more familiar example, the fur on the inside of a 

 tea kettle is carbonate of lime ; and for anything chemistry 



25 tells us to the contrary, the chalk might be a kind of gigantic 

 fur upon the bottom of the earth kettle, which is kept pretty 

 hot below. 



Let us try another method of making the chalk tell us its 

 own history. To the unassisted eye chalk looks simply like 



30 a very loose and open kind of stone. But it is possible to 

 grind a slice of chalk down so thin that you can see through 

 it until it is thin enough, in fact, to be examined with any 

 magnifying power that may be thought desirable. A thin 

 slice of the fur of a kettle might be made in the same way. 



