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BOTANY 



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time. This will occur before all the wood is consumed. Another splinter 

 of wood, placed in a jar with the cover off, will burn slowly but completely. 

 A third piece of wood burned in the air will be quickly and completely 

 consumed. If now a little limewater^ is poured into the jar which was 

 closed, and the contents shaken up, the limewater will be found to turn a 

 milky color. This milky appearance is due to the formation within the jar 



of a material known as calcium carbonate. This 

 is thrown down in the liquid as a result of the 

 union of carbon with lime. Evidently some of 

 the carbon from the wood has passed in the form 

 of a gas into the limewater and there united with 

 the calcium in the lime. Remembering what we 

 know about oxidation, we see that the carbon of 

 the wood has passed ofif and united with oxygen 

 of the air in the jar. Thus, by the uniting of the 

 two chemical elements, a chemical compound has 

 heenformed. The presence of carbon dioxide is 

 known by the fact that it puts out a flame and 

 that it turns limewater milky. This compound 

 is known to chemists as carbon dioxide.^ 



Nitrogen. — There is another gaseous 

 substance that will not support combus- 

 tion; this is the element nitrogen. Its 

 presence in the atmosphere is shown by 

 the following experiment: — 



Invert a bell jar in a large, deep dish of water, 

 having previously placed within the jar on the 

 surface of the water a piece of phosphorus sup- 

 ported on a flat bit of wood or cork. Leave the 

 experiment for at least two days undisturbed (or, 

 the phosphorus may be lighted and then the jar 

 left for a few hours untouched). After that time the water will be found 

 to have risen considerably in the jar.^ If you make a mark on the cover 



* Limewater can be made by shaking up a piece of quicklime the size of your fist 

 in about two quarts of water. Filter or strain the limewater into bottles and it 

 is ready for use. 



2 Chemists have shown that any given structure is made up of molecules. A 

 molecule is the smallest bit of matter that can exist separately and still retain its 

 composition and properties. A molecule is composed of still smaller particles 

 called atoms. Carbon dioxide is so called because its molecule is made up of one 

 atom of carbon and two atoms of oxygen. It is customary to use certain letters 

 or symbols to designate certain chemical elements, as C for carbon, H for hydrogen, 

 N for nitrogen. P for phosphorus, Fe (Latin ferrum) for iron. The molecule of 

 carbon dioxide is made of one part of carbon and two of oxygen ; it is written CO2. 

 This is called the chemical formula. If an electric current is passed through a jar 

 of water, the contents will be broken down into the elements hydrogen and oxygen. 

 If now the gases are carefully collected, there will be found to be exactly twice as 

 much of the hydrogen gas as there is of the oxygen. The chemical formula for 

 water is H2O. See figure. 



^ It would be well for the teacher at this place to bring up.the subject of atrnos- 

 pheric pressure. Air presses down on the earth's surface at sea level with a weight 

 of fifteen pounds to every square inch of surface. 



Apparatus for separating 

 water into the two ele- 

 ments hydrogen and 

 oxygen. 



