ON A PIECE OF CHALK 47 



of this wonderful universe, and of man's relation to it, 

 than the most learned student who is deep-read in the 

 records of humanity and ignorant of those of Nature. 



The language of the chalk is not hard to learn, not 

 nearly so hard as Latin, if you only want to get at the 

 broad features of the story it has to tell ; and I pro- 

 pose that we now set to work to spell that story out 

 together. 



We all know that if we "burn" chalk the result is 

 quicklime. Chalk, in fact, is a compound of carbonic 

 acid gas, 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 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 great 

 many other ways of showing that chalk is essentially 

 nothing but carbonic acid and quicklime. Chemists 

 enunciate the result of all the experiments which 

 prove this, by stating that chalk is almost wholly com- 

 posed of "carbonate of lime." 



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 substance, and is met with under very various 

 conditions. All sorts of limestones are composed of 

 more or less pure carbonate of lime. The crust which 

 is often deposited by waters which have drained through 

 limestone rocks, in the form of what are called stalag- 

 mites and stalactites, is carbonate of lime. Or, to take 



