298 PEROXIDE or HYDROGEN. 



the spark from an electric machine, is brought into 

 contact with the mixed gases, they ignite, explode vio- 

 lently, and combine to form water. The discovery of 

 the composition of water was thus synthetically made 

 by Cavendish its constitution having been previously 

 theoretically announced by Watt.* 



If, instead of combining oxygen and hydrogen in the 

 proportions in which they form water, we compel the 

 hydrogen to combine with an additional equivalent of 

 oxygen, we have a compound possessing many properties 

 strikingly different from water. This peroxide of hy- 

 drogen, as it is called is a colourless liquid, less 

 volatile than water, having a metallic taste. It is 

 decomposed at a low temperature, and, at the boiling 

 point, the oxygen escapes from it with such violence, 

 that something like an explosion ensues. All metals, 

 except iron, tin, antimony, and tellurium, have a, ten- 

 dency to decompose this compound, and separate it into 

 oxygen and water. Some metals are oxidized during 

 the decomposition, but gold, silver, platinum, and a few 

 others, still retain their metallic state. If either silver, 

 lead, mercury, gold, platinum, manganese, or cobalt, in 



pound atmosphere, is the same 

 at all elevations. 



3. When two atmospheres 

 are mixed, they continue so 

 without the heavier manifesting 

 any disposition to separate and 

 descend from the lighter. 



of each in the compound at- 

 mosphere gradually vary in the 

 ascent. 



8. When two atmospheres 

 are mixed, they take their places 

 according to their specific gra- 

 vity, not in separate strata, but 

 intermixedly. There is, how- 

 ever, a separate stratum of the 

 specifically lighter atmosphere 

 at the summit over the other. 



* The discussion of this question, commenced by Arago in his 

 Eloge, was continued by Lord Brougham in his Lives of Watt and 

 Cavendish, and by Mr. Yernon Harcourt, in his address as Presi- 

 dent of the British Association, and more recently in his Letter to 

 Lord Brougham. Watt's Letters on the subject have been since 

 published under the superintendence of Mr. Muirhead. 





