268 HYDROGEN. 



commended by Thenard to dissolve the peroxide of barium in 

 hydrochloric acid considerably diluted with water, and to re- 

 move the barytes by sulphuric acid, which forms an insoluble 

 sulphate of barytes. The hydrochloric acid, again free in the 

 liquor, is saturated a second time with peroxide of barium and 

 precipitated ; and after several repetitions of these two opera- 

 tions, the hydrochloric acid itself is removed by the cautious 

 addition of sulphate of silver, and the sulphuric acid of the last 

 salt by solid barytes. Such is an outline of the process ; but 

 its success requires attention to a number of minute precautions 

 which are fully detailed in the Traite de Chimie of the author 

 quoted.* The weak solution of peroxide of hydrogen, which 

 this process affords, may be concentrated by placing it with a 

 vessel of strong sulphuric acid under the receiver of an air 

 pump, until the solution attains a density of 1.452, when the 

 peroxide itself begins to rise in vapour without change. It then 

 contains 475 times its volume of oxygen. 



M. Pelouze abridges this process considerably by employing 

 hydrofluoric acid or fluosilicic acid, in place of hydrochloric 

 acid, to decompose the peroxide of barium. By this operation, 

 the barytes separates at once with the acid, in the state of the 

 insoluble fluoride of barium, and nothing remains in solution 

 but the peroxide of hydrogen. After thus decomposing several 

 portions of peroxide of barium successively in the same liquor, 

 the fluoride of barium may be separated by filtration, and the 

 peroxide of hydrogen, which is still dilute, be concentrated by 

 means of the air-pump. 



Properties. Peroxide of hydrogen is a colourless liquid re- 

 sembling water, but less volatile, having a metallic taste, and 

 instantly bleaching litmus and other organic colouring matters. 

 It is decomposed with extreme facility, effervescing from 'escape 

 of oxygen at a temperature of 59, and when suddenly exposed 

 to a greater heat, such as 212, actually exploding from the 

 rapid evolution of the gas. It is rendered more permanent by 

 dilution with water, and still more so, by the addition of the 

 stronger acids, while alkalies have the opposite effect. 



The circumstances attending the decomposition of this body 

 are the most curious facts in its history. Many pure metals 

 and metallic oxides occasion its instantaneous resolution into 



* Vol. I, page 479 of the 6th edition. 



