DIFFUSE CHEMICAL ACTIONS 



339 



Oxygen. Various forms of gas-chamber may be used to follow the 

 influence of the withdrawal of oxygen upon streaming, and the partial 



FlG. 58. Apparatus for obtaining pure hydrogen and pure carbon dioxide free from all oxygen, 

 connexions are submerged in water, and all the liquids are covered with a layer of liquid paraffin. (The g 

 one-tenth and the remaining apparatus one-sixth natural size. After Ewart.) 



CAll the 

 generators 



pressure of oxygen may either be reduced by the aid of an air-pump 

 attached to (c) Fig. 57, or by displacement with a neutral gas entering 

 at the other tube. In the former case, the cover-slip (#), to which the 

 hanging drop with the object is attached, must either be small or thick, 

 and must be sealed on by vaseline stiffened with colophonium or wax. 

 A still better attachment is given by melted shellac. To produce a complete 

 absence of oxygen evacuation and the passage of hydrogen must be 

 frequently repeated. A steady supply of pure oxygenless hydrogen can 

 be obtained by the apparatus shown in Fig. 58, in which all the connexions 

 are under water covered with liquid paraffin, and the gas, after passing 

 through purifying tubes, is deoxygenated by pyrogallol and caustic potash 1 . 



1 A better form of gas-chamber is that figured on p. 315 (Fig. 52), by which the influence of 



Z 2 



