252 Domestic Science 



equal to the decrease in the volume of the air in the 

 earlier part of the experiment. The gas left in the 

 bell -jar was shown to be irrespirable and a non-supporter 

 of combustion, while that obtained by heating the red 

 powder gave evidence of possessing the opposite charac- 

 teristics to a marked degree. 



The repetition of the first part of Lavoisier's experi- 

 ment cannot be readily carried out, but we may test 

 the latter portion with ease by repeating Experiment 44, 

 since the red oxide of mercury used in that experiment 

 is no other than the red powder formed in Lavoisier's 

 experiment. The change of the mercury into the red 

 powder is expressed by the chemical equation : 

 Mercury + oxygen = mercury oxide. 



The reverse change brought about in the later stage of 

 the same experiment is written thus : 



Mercury oxide = mercury -f oxygen. 



A somewhat similar method is made use of to 

 obtain large supplies of oxygen from the air by the 

 manufacturing process known as "Erin's process". 

 In this, barium oxide is heated in air under pressure, 

 when it combines with oxygen to form barium dioxide. 

 This substance is then heated at the same temperature 

 under a very much reduced pressure, and the oxygen 

 with which it combined previously is set free. 



Equations : 



Barium oxide + oxygen = barium dioxide ; 

 Barium dioxide = barium oxide + oxygen. 



170. Oxygen may also be obtained by the action 

 of heat on many other oxides. 



EXPERIMENT 107. Treat some red lead oxide 

 commonly known as red lead in a similar fashion to 



