158 CHEMISTRY. 



out as we carry them about. 1 85. In what two ways does water act in put- 

 ting out fires ? Explain other means of putting out fires. 186. How can 

 a fire be made under water? 187. What is said about fire extinguishers? 

 Explain the extinguishing of a fire in a Scotch coal-mine. 188. What is the 

 oxyhydrogen blow-pipe? \Vhat is its use? 189. What is the Drummond 

 Light? What the oxycalcium light? When are they used? 190. Ex- 

 plain the cause of explosions. What causes the noise? 191. Describe the 

 hydrogen pistol, and the experiment with soap-bubbles? 192. What is 

 spontaneous combustion? State and explain the experiment with phos- 

 phorus and charcoal. Give various examples of spontaneous combustion. 

 193. Is oxygen indispensable to combustion ? 194. What are the requi- 

 sites for ordinary combustion ? Give examples illustrating the variation of 

 these in different cases. 195. What is said of ordinary oxidation ? 196. 

 What of sun-bleaching ? 197. How is animal heat the result of combus- 

 tion? 198. What facts show that animal heat is not made in the lungs? 

 Where is it made? 199. What is the temperature of the body? What is 

 said about the body's giving out heat ? 200. What is the fuel of the fire in 

 the body ? What is said of the sources of the fuel ? What of the uses 

 sometimes made of the fat of the body? 201. What of the amount of the 

 fuel used ? 202. How is the windpipe the smoke-pipe of the body ? 203. 

 Show how exercise influences animal heat. 204. What is said of cold- 

 blooded animals ? 205. What is said of hibernating cold-blooded animals ? 

 What of hibernating warm-blooded animals ? 206. What is said of the 

 four chief elements ? 207. What is the nature of the changes in air and 

 water? - 



CHAPTER XL 



CHLORINE, BROMINE, IODINE, AND FLUORINE. 



208. A Natural Group. Having now studied somewhat 

 at length the most important and widely distributed ele- 

 mentary bodies oxygen, nitrogen, carbon, and hydrogen 

 together with many of the compounds which they form, we 

 will now take up the remaining elements one by one, and, for 

 convenience' sake, will begin with the non-metals not yet 

 described. Four of these non-metals chlorine, bromine, io- 

 dine, and fluorine resemble each other, chemically speak- 



