142 METALLOIDS. 



dry mixture in a test-tube, connected, air-tight, with two 

 clay pipes, as represented in the figure. The connec- 

 tions are made by winding the pipe-stems with strips 

 of wet paper, folded in such a manner that the stopper 

 thus formed tapers slightly toward the end. The first 

 portions of gas, which contain an admixture of the air of 

 the tube, are allowed to bubble through the water, and 

 escape. The rest is made to rise into a half-pint vial, 

 which it gradually fills, by displacing the water. The 

 vial has previously been filled with water, then 

 covered with a bit of glass, inverted in the wa- 

 ter. If it is desired to hang it on the side of the 

 bowl, a hook is then introduced, made of strong, 

 doubled wire, the two parts being kept about half 

 an inch apart, and the vial is then hung, by its help, on 

 the side of the bowl ; or this may be dispensed with, 

 and the vial held by the hand in its proper place, while 

 the gas is collected. When the process is completed, 

 vial and hook, if the latter has been used, are to be low- 

 ered into the bowl, the mouth being carefully kept 

 below the surface ; the hook is then removed, the mouth 

 covered with a bit of glass, and the vial then inverted 

 upon a plate containing a little water, and so kept until 

 it is wanted for an experiment. All other gases, that 

 are not absorbed by water, may be collected in the 

 same manner. 



Explain the 332. EXPLANATION. Although black 



process. oxide of manganese may be employed as 



a source of oxygen, it does not yield this gas at the 

 temperature employed in the above experiment. But, 



