122 



CHEMISTRY. 



[ lesson X. 



fall ill little globules, cracked the bottle. 

 "NVhen this experiment is performed the 

 jar should not be moved from the trough, 

 and the greased glass placed at the upper 

 part, by this means the metal will fall in 

 the water. 



110. T. Is there anything peculiar 

 about these globules ? 



P. Yes ; they are found to weigh more 

 than the actual metal used, thus proving 

 that they have combined with something 

 which has weight ; this is oxygen, and the 

 globules at the bottom of the trough are 

 masses of black oxide of iron. 



111. T. Can you give me any other 

 experiments to illustrate its properties? 



P. Yes, but some of them are very 

 dangerous ; and we have performed enough 

 to show that it supports combustion, and 

 readily combines with many substances. 



112. T. Is oxygen necessary to our 

 existence ? 



P. Undoubtedly, but not in a pure 

 state. You know that it is found in the 

 air combined with nitrogen, in water com- 

 bined with hydrogen, with metals forming 1 

 oxides, in the tissues of vegetables and 

 animals, and in our blood. 



113. T. "NY hat do you mean by oxygen 

 forming oxides with metals ! 



P. The gas combines and forms a com- 

 pound which is called an oxide. These 

 oxides are divided into three principal 

 groups ; 1. Those which resemble potash, 

 soda, or the oxide of lead in their chemical 

 relations, called alkaline or basic oxides, and 

 sometimes salifiable bases. 2. Those which 

 have properties directly opposed to the 

 first group, called acids, which have a strong 

 tendency to unite with the salifiabK 

 such as sulphuric acid and potash to form 

 the salt sulphate of potash. 3. The 

 neutral oxides, such as black oxide of 

 manganese, which show little inclination 

 to unite with other substances. 



GENERAL QUESTIONS ON LESSO 



1. How are gases collected, and what 

 apparatus is required ? 



3. Describe the processes of obtaining 

 oxygen. 



4. Give the properties of this gas. 



5. Illustrate its properties by experi- 

 ments. 



G. Is oxygen essentially necessary ? 

 7. "Why does oxygen exist in com- 

 bination, and not pure . ; 



LESSON X. 



"WATER consists of the two elements oxygen and hydrogen : we have examined the 

 former, and it will now be our duty to consider the Litter. When we procured oxygen 

 we employed heat, but it is not required in the preparation of hydrogen, the apparatus 

 being very simple, merely consisting of a common flask, or bottle, fitted with a good 

 cork through which a tube-funnel (b) passes, to enable us to pour liquid into the bottle, 

 and a gas-delivering tube (a) is also inserted into it, as in Fig. 32. 



QUESTIONS. 



114. T. "What is hydrogen ? 



P. A gaseous body which we are un- 

 able to liquefy either by cold or pressure. 

 It is inodorous, colourless, and tasteless 

 when quite pure ; and has a very low 

 specific gravity compared with that of any 

 other form of ponderable matter, being 

 0.069, while atmospheric air is estimated 

 at 1,000. 



115. T. What do you mean by pon- 

 derable matter ? 



p. Anything that has weight is said to 

 \>cponderable, such as oxygen and hydrogen 



gases; but certain things that cannot be 

 weighed, like light, heat, and electricity, 

 are called imponderable*. 



[See Q. 111. p. 22.] 



116. T. What is the name hydrogen 

 derived from ? 



P. Two Greek words, udoor, (i>5up), 

 water, and gcnnao, (yevvaw], I give HM.- 

 to ; it signifies a producer of water. 



117. T. How can we obtain hydrogen ? 

 P. By several methods. For example, 



if we wish to do so for experimental pur- 

 poses, we usually place some granulated 



