CH. II] GAS EVOLVED. 33 



readings are obtained, cover the beaker with a double 

 bell-jar containing ammoniacal copper-sulphate solution 

 and note the result. After an interval of ten minutes, 

 when the readings should be approaching constancy, 

 replace the blue jar by another containing potassium 

 bichromate solution, and take a series of readings. It will 

 probably be necessary to alternate the blue and orange 

 light several times before a definite result is obtained. 



(47) Collection of the gas. 



Place a quantity of any of the above-named water- 

 plants in a glass jar of about 12 — 14 cm. diameter. 

 Press the plants down into the water with an inverted 

 funnel, which should be a large one, and should fit easily 

 inside the jar ; its neck should be cut short, so that the 

 opening may be easily submerged. The gas given off by 

 the plants will be guided by the funnel and may be 

 collected in an inverted test-tube filled with water and 

 placed over the opening. If the neck of the funnel is 

 covered with ^ inch of india-rubber tubing, and if a 

 test-tube be selected which fits tightly over the tube, no 

 other support for the test-tube is needed. The funnel 

 may be kept in its place by 3 bent glass rods hooked over 

 the rim of the jar, and ending in glass rings by which they 

 are tied to the neck of the funnel. 



When the test-tube is nearly full, the gas may be 

 shown to be oxygen by the glowing of a splinter of deal 

 which has been lighted, and is blown out just before it is 

 thrust into the gas. The test-tube should be of such a 

 size that it can be easily covered with the thunib. 



D. A. 3 



