produced by Platinum. 45 



gender out of free oxygen and water a highly oxidizing per- 

 oxide, which surrounding that metal empowers the latter to 

 cause all the oxidations above mentioned. In comparing the 

 chemical properties of platinum, when minutely divided, with 

 those of ozone, we cannot help being struck by their great simi- 

 larity, as will appear from the following statements : — 



1. Both substances possess a negative electro-motive power. 



2. Both of them destroy organic colouring matters. 



3. Both of them render the resin of guaiacum blue. 



4. Both of them decompose iodide of potassium. 



5. Both of them change the yellow prussiate of potash into 

 the red one. 



6. Both of them transform sulphurous acid into sulphuric 

 acid. 



7. Both of them decompose oxalic and formic acids. 



8. Both of them act in a similar way upon aether and alcohol. 



Great as the similarity of properties may be, it does not fol- 

 low that platinum owes its oxidizing powers to a film of per- 

 oxide of hydrogen being formed round the metal by a cata- 

 lytical action of the latter. I have not yet succeeded in pro- 

 ducing, by the means of spongy platinum and moist air, an 

 atmosphere exhibiting the peculinr electrical smell, bleach- 

 ing power and oxidizing properties which belong to ozone. 

 Considering the great volatility of the last-named substance, 

 we should suppose that it ought to disperse into the sur- 

 rounding medium as soon as formed; or should ozone be re- 

 tained by platinum in a way similar to that in which we think 

 oxygen is attached to and condensed around that metal ? Sup- 

 posing oxygen to be an odoriferous substance, it is manifest 

 that the oxygen actually condensed by platinum could not 

 affect the olfactory nerves. 



Another objection might be raised to the conjecture, that it 

 is a film of peroxide of hydrogen, to which platinum owes its 

 oxidizing powers, from the fact that Thenard's oxygenized 

 water is really decomposed by platinum. Considering how- 

 ever that ozone is in some respects strikingly different from 

 Thenard's compound, having for instance a peculiar odour, 

 being insoluble in water, transforming both metallic silver 

 and its basic oxide into a peroxide, it appears possible that 

 ozone is capable of existing in the closest contact with pla- 

 tinum without suffering decomposition. I am not aware of 

 spongy platinum or platinum black having been treated with 

 anhydrous oxygen, and I do not know whether it has been 

 ascertained if the latter is absorbed as easily by that metal 

 as moist oxygen. It is equally unknown to me whether 

 platinum, after being placed in dry oxygen or air, exhibits 



