42 Dr. Schcenbein on some Chemical Effects 



mentioned are able to render blue paste of starch, another 

 proof that there is no free iodine in the case. The reaction 

 described is most likely brought about in the following man- 

 ner: the chemically excited oxygen surrounding the spongy 

 platinum decomposes iodide of potassium, a peculiar peroxide 

 of potassium being formed and iodine eliminated. The latter 

 in its nascent state combines with platinum to produce the 

 periodide of that metal, which itself unites with iodide of po- 

 tassium into that compound, yielding with water a red solu- 

 tion. It is worthy of remark, that a solution of iodide of 

 potassium having been treated with spongy platinum, enjoys 

 the property of colouring blue the paste of starch on being 

 mixed with dilute and pure sulphuric acid. The same re- 

 action is exhibited by the same solution after it has been 

 treated either with ozone or peroxide of lead. If some drops 

 of a weak, i. e. colourless solution of the yellow prussiate of 

 potash, be added to platinum black, that solution assumes a 

 perceptibly yellow colour, and yields with a solution of che- 

 mically pure sulphate of protoxide of iron a blue precipitate. 



From these facts, it seems to follow that platinum has 

 the power to transform the yellow prussiate into the red one. 

 Some years ago I tried to show that spongy platinum being 

 placed in an atmosphere of sulphuretted hydrogen, loses its 

 property of acting upon detonating gas, on account of a film 

 of sulphur being deposited on the surface of the metal. Such 

 being the case, it would follow that spongy platinum has the 

 property to decompose sulphuretted hydrogen. 



Colourless hydriodic acid, on being mixed up with some 

 platinum black, assumes a brownish yellow colour, which re- 

 action indicates an elimination of iodine. 



Several chemists, particularly Dcebereiner, Phillips, and 

 Brunner, have ascertained that spongy platinum produces sul- 

 phuric acid on being placed in contact with moist oxygen and 

 sulphurous acid, and there is no doubt that platinum black 

 put into sulphurous acid gives rise to the formation of sul- 

 phuric acid. Moist filtering-paper being coloured by a solu- 

 tion of indigo and put in contact with spongy platinum for 

 about twenty-four hours, appears entirely bleached at those 

 spots which had touched the metal. I have repeated this ex- 

 periment more than thirty times, and always with the same 

 result. This remarkable fact proves that platinum in a state 

 of minute mechanical division, has the power of destroy- 

 ing organic colouring matters, and acts as a real bleaching 

 agent. Before passing to other subjects, I must not omit 

 to mention a circumstance which seems to me meriting some 

 attention. It is a curious fact, which has not escaped the 



