148 ELECTRICITY. 



Questions. — 1. What is an oxyd ? 2. What are the principal 

 ways by which metallic oxyds are formed ? 3. What is said of iron as 

 an example ? 4. What is red lead and how ia it made ? 5. What is 

 said 01 me di^erent capacity and attraction of metals for oxygen ? 6. 

 What experiment is given for illustration ? 7. What is said of the 

 properties of nitrous oxyd gas ? 8. What effects does it produce on 

 being inhaled ? 0. How may it be procured ? 10. How may combus- 

 tion be defined ? 11. How is the process of combustion explained.'' 

 12. What remains when the combustion is over ^ 13. What is smoke .' 



14. How may the agency of oxygen in combustion be demonstrated ? 



15. What becomes of the nitrogen gas .■* 16. What is said of the in- 

 destructibility of matter .'' 17. What is a retort ^ (see Appendix.) 

 18. How may chlorine be procured ? 10. What is said of the attrac- 

 tion of chlorine for the metals ? 20. How is combustion defined in the 

 Appendix, and oa what grounds is it so defined ? 



LESSON 67. 



Electricity. 



Elec'tric. The first electrical phenomena are supposed to have 

 been observed in a mineral substance called ai.iber, in Greek 

 elektron, and hence the fluid or power has been denominated 

 electric. 



The surface of the earth, and of all the bodies with which 

 we are acquainted, is supposed to contain or possess a power 

 of exciting or exhibiting a certain quantity of an exceed- 

 ingly subtile a-rent, called the electric fluid or power. The 

 quantity usually belonging to any surface, is called its natu- 

 ral share, and then it produces no sensible effects ; but when 

 any surface becomes possessed of more, or of less, than its 

 natural quantity, it is electrified, and it then exhibits a variety 

 of peculiar and surprising phenomena ascribed to the power 

 called electric. If you take a stick of sealing-wax and rub 

 it on the sleeve of your coat, it will have the power of at- 

 tracting small pieces of paper, or other light substances, 

 when held near them. If- a clean and dry glass tube be 

 briskly rubbed with the hand, or with a piece of flannel, 

 and then presented to any small light substances, it will im- 

 mediately attract and repel them alternately for a consider- 

 able time. The tube is then said to be excited. If an ex- 

 cited glass tube, in a dark room, be brought within about 

 half an inch of the finger, a lucid spark will be seen between 

 the finger and the tube, accompanied with a snapping noise, 

 and a peculiar sensation of the finger. Dry flannel clothes, 



