32 AGRICULTURAL CHEMISTRY 



angles, and in an opposite direction from the first bend (Fig. 13)' 

 Fit to the test-tube a cork, perforated as directed in Section 26, and 

 insert the delivery tube. Fill the pneumatic trough nearly full of 

 water, and place in it the free end of the delivery tube (Fig. 14). 

 Weigh out 5 grams each of potassium chlorate (KC1O 3 ) and man- 



Fig. 14. Preparation of oxygen. Pneumatic trough. 



ganese dioxid (MnO 2 ). Mix on a sheet of paper, and place the 

 mixture in a test-tube. See that the test-tube is perfectly dry, both 

 inside and out. Fill the cylinders with water, cover with glass 

 plates and place them inverted on the shelf of the pneumatic trough. 

 With a medium-sized flame, apply heat cautiously to the test-tube. 

 The flame should be moved from time to time, and not allowed to 

 strike just one part of the test-tube, otherwise the glass will melt, 

 and the test-tube collapse. As soon as bubbles of gas are given off 

 freely from the water, place the end of the delivery tube so that 

 the gas is collected in one of the cylinders. When a cylinder 

 is filled, cover it with one of the glass plates, while the mouth of 

 the cylinder is still under water. It can then be placed upright 

 upon the desk, and another cylinder filled with O. After collect- 

 ing three or four cylinders of gas, remove the end of the delivery 

 tube from the water, and then remove the flame. Do not remove 

 the flame while the end of the delivery tube is under water, or a 

 vacuum will be formed, and the water will rush back into the test- 

 tube. Tests should be made with the O as follows : 



(i) Light a splinter and place it for a moment in one of the cyl- 

 inders of oxygen (see Fig. 15) ; remove it ; extinguish the flame, 



