130 CALORIC. 



The simple substances were said very lately to amount to 

 more than fifty in number, but since the truly interesting 

 and very important discoveries of Sir Humphrey Davy, and 

 other eminent chemists, it is scarcely possible to say what 

 substances are not compound bodies. But it will be most 

 conducive to science to consider all those substances as 

 simple, which no mode of decompounding has yet been dis- 

 covered. Simple substances naturally divide themselves 

 into two classes. Those which belong to the first class 

 are of too subtile a nature to be confined in any of the ves- 

 sels which we possess. They do not sensibly affect the most 

 delicate balance, and they have received therefore the name 

 of itiiponderahle bodies. The second class of bodies may be 

 confined in proper vessels, may be exhibited in a separate 

 state, and their weight and other properties may be deter- 

 mined. They have received the name o^ pondei^ahle bodies. 

 The imponderable bodies at present supposed to exist are 

 four, light, heat or caloric, electricity, and magnetism. The 

 first three are intimately connected with chemistry, but mag- 

 netism has with it no known connexion. 



Questions. — 1. What is the object of chemistry? 2, How does 

 the science divide itself ? 3. What is meant by simple substances? 

 4. What is the difference between decomposition and division ? 5. 

 How are compound bodies formed ? C. What is attraction and its 

 most obvious instances ? 7. Define attraction of cohesion and attrac- 

 tion of composition. 8. Wliat are the results of each of these kinds 

 of attraction ? 9. What example is given to illustrate chemical affini- 

 ty or attraction ? 10. How may you decompose the body thus formed ? 

 11. Define the chemical term precipitate. 12. What is said of the 

 number of simple substances? 13. Into what two classes are they di- 

 vided ? 14. What is stated as the ground of this division ? 15. What 

 are the four imponderable bodies ? 



LESSON 60. 



Caloric. 



Chem'ically, when a mere mixture of two or more substances is 

 made, they are said to be mechanically united ; but when each 

 or either substance forms a component or constituent part of the 

 product, the substances have formed a chemical union. 



Heat is a well known sensation which we perceive on 

 touching any substance whose temperature is superior to 



