RESPIRATION 117 



the lighted end of a splinter or taper is placed in the empty 

 bottle it is not extinguished soon because the suffocating gas 

 was not present.* In time, however, it may be extinguished 

 owing to the accumulation of the carbon dioxide from the burning 

 splinter. 



This experiment teaches us that the suffocating gas (carbon 

 dioxide) is given off in quantity by the peas during germination. 

 That it is carbon dioxide is shown by the white precipitate when 

 the barium hydrate is poured down the inside of the bottle. 

 Some of the element barium unites with some of the carbon 

 dioxide by chemical change and forms barium carbonate, which 

 is the white precipitate. 



In this experiment care must be taken to test with the barium 

 hydrate before holding the flame in the bottle of peas. It is 

 much better to have a separate bottle of peas for the test with 

 the flame. This is because carbon dioxide is formed during 

 the burning of the splinter. To show this pour some barium 

 hydrate down the inside of the empty bottle after the flame has 

 been held in it. To show that animals also exhale carbon 

 dioxide while they breathe, take a shallow vessel of baryta water 

 and breathe on the water several times. A thin film of the white 

 precipitate (barium carbonate) is formed on the surface of the 

 barium hydrate, f 



187. The germinating seeds take oxygen gas from the air 

 while they breathe. A simple experiment will show this. A 

 handful of wheat is soaked in water, and then placed in a germi- 

 nator (a moist vessel) in the folds of a wet cloth. When it has 



* The extinguishing of the flame does not prove that CO 2 is present. 

 That has been proven by the former experiment, and since we know by this 

 that CO 2 is present it is fair to conclude that this is the gas in this instance 

 which extinguishes the flame. 



f Lime water may be used instead of baryta water for all the above ex- 

 periments, but it is not so satisfactory as baryta water because the result is 

 not so striking. To make lime water place a lump of lime twice as large 

 as a hen's egg in a quart of water. Allow it to settle and in a day or two filter 

 the liquid and keep corked tightly in a bottle. The white substance formed 

 when lime water is used is calcium carbonate, or carbonate of lime. 



