produced by Platinum. 41 



same manner as that metal occasions the oxidation of hy- 

 drogen, aether and alcohol. The facts I am going to state 

 will show that the correctness of this conjecture is fully borne 

 out by experiment. 



Newly-prepared spongy platinum being placed upon a piece 

 of filtering paper that had previously been drenched with an 

 alcoholic solution of resin of guaiacum, caused rather rapidly 

 the appearance of blue spots at the place where the metal had 

 been in contact with the resinous solution. My experiments 

 have further shown that that reaction takes place the more ra- 

 pidly and intensely the more divided the platinum happens to 

 be of which we make use in the experiment described. What 

 is called Platinum Black acts therefore more energetically 

 than spongy platinum does. From the facts stated, it appears 

 that platinum in a state of minute mechanical division con- 

 ducts itself towards resin of guaiacum like the simple' halo- 

 genous bodies, ozone and a number of metallic peroxides. 

 These facts demonstrate also that the coloration of the resin- 

 ous matter being caused by platinum, belongs to that series 

 of phaenomena which takes place when that metal is put in 

 contact with a mixture of oxygen and hydrogen, oxygen and 

 vapour of aether, &c. 



In the paper above alluded to, I have pointed out the re- 

 markable coincidence that all the substances having the 

 power of rendering blue the resin of guaiacum possess also the 

 property of decomposing iodide of potassium, transforming 

 the yellow prussiate of potash into the red one, and I add, 

 decomposing sulphuretted and ioduretted hydrogen, trans- 

 forming sulphurous acid into sulphuric acid, and destroying 

 organic colouring matters. We shall presently see that pla- 

 tinum in a state of minute mechanical division has the same 

 power. 



If a crystal of pure iodide of potassium be put upon a piece 

 of filtering paper that has previously been moistened with di- 

 stilled water and spongy platinum be placed upon that paper, 

 the spot touched by the metal assumes rather rapidly a brown- 

 ish red colour. This coloration does not result from free iodine, 

 but is most likely due to a compound consisting of periodide 

 of platinum and iodide of potassium. That conjecture is 

 founded upon the following facts. If a solution of iodide of 

 potassium is put in contact with spongy platinum, or platinum 

 black, the former assumes a perceptibly red colour, which dis- 

 appears on heating the solution to its boiling-point. Now it 

 is well known that the compound before mentioned yields with 

 water a red solution, the colour of which is destroyed by heat. 

 Neither the red solution nor the brownish-red spots before 



