110 CHEMISTRY. 



of the air in respiration ? How in contrast with oxygen in combustion ? 

 How is the nitrogen of the air lessened ? What is said of the nitric acid 

 formed in the air? 133. How can you show that air is contained in water? 

 134. What is said of the composition of the air that is in the water? 

 135. Describe the experiment with snow. 13G. What is said of the chem- 

 ical exchange between plants and animals in water? 137. What is said 

 of the moisture in the air ? Trace the analogy between this and the solu- 

 tion of solids in a liquid. 138. What is said of the diffusion of impurities 

 in the air? How is it purified from them? 139. For what reasons was 

 the air formerly thought to be a compound ? What are the proofs that it 

 is a mixture ? 



CHAPTER IX. 



THE CHEMISTRY OF WATER. HYDROGEN. 



140. Constituents of Water. "Water, though a fluid, is 

 composed of two gaseous elements. With the properties 

 of one of these, oxygen, you have already become well ac- 

 quainted. The other gas is hydrogen, so called because 

 when chemically united with oxygen it produces water, the 

 name being derived from two Greek words hudor, water, 



and gennao, I form. In form- 

 ing water, two volumes of 

 hydrogen unite with one vol- 

 ume of oxygen, or two parts 

 2 vols. + 1 vol. = 2 vols. ^7 weight of the former with 



Oxygen 88.9 per cent. Sixtee " P artS ** Wci ? ht f 



Hydrogen 11.1 * " ie wtjMT. All this is pre- 



Water Tooo sented to the eye in the di- 



PI& ^ agram, Fig. 34 the spaces 



representing the proportions 



of the two ingredients in bulk, and the figures their propor- 

 tionate weights. You will notice that owing to the con- 

 traction which takes place, two volumes of water result 



H 2 O 18 



