THE FOOD OF THE PLANT 



41 



Experiment 23 



Aim. — To prepare and collect carbon-dioxide and to 

 test its properties. 



Method.— Put about 20 grammes of limestone, or 

 marble broken into small 

 pieces, into a flat-bottomed 

 flask, fitted with a thistle- 

 funnel and delivery-tube. 



A two-necked bottle is con- 

 venient, but an ordinary flask 

 fitted with a two-holed rubber- 

 stopper answers quite well. A 

 rubber-stopper is better than 

 a cork, as it is difficult to get 

 the latter air-tight. 



The delivery-tube should be bent as shown in Fig. 18 

 or Fig. 19. 



Cover the marble with water and add a little concen- 

 trated hydrochloric acid through the funnel. The 

 funnel need not necessarily have a tap, but, if there 

 is no tap, care must be taken that the stem of the 

 funnel reaches the liquid in the flask, otherwise the gas 

 evolved will escape through the funnel. 



The gas is readily given off without the application 

 of heat. It may be collected either over water as 

 oxygen was collected (Fig. 18), or by down- 

 ward displacement of air (Fig. 19). 



Observations. — 1. The gas is colourless 

 and invisible. It has a faint, pungent 

 smell. 



2. The bubbles appear to get rather 

 smaller as they rise through the water, 

 thus suggesting that the gas is some- 

 what soluble. 



The solubility may be further tested in the following 

 way: A jar of the gas is opened under water; the 

 plate is replaced so that a small quantity of water is 

 enclosed; the jar is well shaken and again opened 

 under water. The water then rises very gradually in 



U 



Vsasi 



Fig. 19 



