THK A WA KEN ING OF THK SEED 35 



rubber stoppers or cork stoppers which have been 

 soaked in melted paraffin (obtainable at grocers' ; we 

 may also obtain it in the form of paraffin candles). 

 Pierce the stoppers with closely fitting glass tubes 

 long enough to reach nearly to the bottom of the. 

 bottle. Place seeds in one bottle to the depth of an 

 inch; leave the other bottle empty. Support both 

 in an inverted position (by means of clothes-pins and 

 rubber bands or wire, as shown in the figure) , allow- 

 ing the tubes to dip into a strong solution of lye. As 

 the carbon dioxide is formed it will be absorbed by 

 the lye, which will rise in the tube and thus indicate 

 the amount produced. 



When carbon unites with oxygen we say that it 

 burns. Whether we burn wood, coal, oil or alcohol, 

 the principal combustible substance is the carbon, 

 which, by uniting with the oxygen, produces carbon 

 dioxide and sets free heat. The heat of our bodies is 

 due to the same process of burning and the carbon 

 dioxide is given off in the breath, as is easily shown 

 by placing one end of a tube under lime-water and 

 blowing into it. The carbon of the body burns, but 

 it does so very slowly. In the seed the process is still 

 slower. The slight degree of heat set free can be meas- 

 ured by carefully comparing two thermometers (by 

 placing them side by side in water at various tempera- 

 tures and comparing their readings) and then arranging 

 them as shown in Fig. 32. One tumbler is filled with 



