222 SMITH'S INTERMEDIATE CHEMISTRY 



For manufacturing purposes it is more convenient to use barium 

 peroxide BaO 2 , suspended in water, and sulphuric acid: 



BaO 2 + H 2 S0 4 - BaS0 4 I + H 2 2 



because the precipitation of insoluble barium sulphate carries 

 the reaction to completion. The precipitate is filtered off and a 

 clear solution of hydrogen peroxide obtained. 



In pharmacy a 3 per cent solution is the one commonly sold, 

 As hydrogen peroxide decomposes rapidly at 100, the pure sub- 

 stance can be obtained only by distilling off the water under re- 

 duced pressure. 



Properties. Hydrogen peroxide . is a colorless, syrupy 



U^Cl,fc(^e^f- -*- o,^te*|P**pr>x -' 



liquid of sp. gr. 1.5, yg^ggjoZe., with water ' in' all proportions. 

 Dilute solutions have a metallic taste. 



Chemical Properties. 1. In water solution, hydrogen peroxide 

 is a weak acid. It enters into double decomposition, particularly 

 with bases, giving salts containing the bivalent radical 2 : 

 Ca(OH) 2 + H 2 2 -> Ca0 2 1 + 2H 2 0. 



2. When the solution is heated, the compound decomposes, with 

 evolution of heat, giving water and oxygen : 



Contact agents hasten the decomposition. Thus, it takes place 

 with frothing when the cold solution is applied, as an antiseptic, 

 to cuts or sores, or when powders, such as manganese dioxide, are 

 thrown into the solution. 



3. Since hydrogen peroxide, like ozone, gives off oxygen with 

 liberation of energy, it is an oxidizing agent also. In this respect 

 its behavior is very similar to that of ozone. It oxidizes colored 

 organic compounds to colorless ones, and is, therefore, used in 

 bleaching hair, feathers, silk, and ivory. It is also fatal to micro- 

 organisms, and is, therefore, employed in medicine to disinfect 

 wounds and as a throat wash. 



In oil paintings the high lights are produced in part with white 

 lead (carbonate of lead). These disappear and the picture darkens 



