40 Dr. Schoenbein on some Chemical Effects 



learnt the art of cross-examining nature, and the latter has 

 not. The difference between the man who has a genius for 

 inductive philosophy, and the man who has none, is — that 

 the one has a sagacity, which the other wants, in discovering 

 media of proof, and driving his interrogatories to a point. 

 Little or nothing depends on the multiplication of experi- 

 ments, everything on the selection ; and the only guides to 

 selection are, first, a quick analogical perception — and, se- 

 condly, a just and sound appreciation — of the causes of phe- 

 nomena. 



Errata in Vol. xxvm. 



Page 489, line 24, for 1764 read 1664. 

 ... 492, ... 5, for " consumes it" read "it is consumed." 

 ... 492, ... 36, for 1764 read 1664. 

 ... 495,... 43, for 1764 read 1664. 



... 514, ... 5, for "duodecimo volume, of scarce a hundred pages" 

 read " treatise of scarce seventy pages." 



XI. On some Chemical Effects produced by Platinum. 

 By Dr. C. F. Schosnbein*. 



COME time ago I published an account of a series of expe- 

 *~ riments made with the resin of guaiacum, from which it 

 appeared that the substance named is instantly rendered blue, 

 not only by chlorine and nitrous acid, but also by bromine, 

 iodine, ozone, and a number of metallic peroxides. 



Free oxygen, be it pure or mixed with nitrogen, hydro- 

 gen, and carbonic acid gas, does not act in the dark upon that 

 resinous matter, and comparatively very little when exposed to 

 the action of solar light. From these facts, it becomes mani- 

 fest that oxygen must have assumed a peculiar condition of 

 chemical excitement before it is capable of causing the re- 

 action mentioned. The beautiful experiments both of Davy 

 and Dcebereiner have demonstrated that platinum has the 

 power to occasion the oxidation of a number of substances 

 under circumstances in which that chemical action would 

 not take place without the agency of that metal. The 

 blue coloration which the resin of guaiacum assumes under 

 certain circumstances is most likely dependent upon a partial 

 oxidation of that substance, and the latter being so very sen- 

 sible to oxygen, that happens to be chemically excited, it 

 could easily be conjectured that platinum in a state of minute 

 mechanical division put in contact with the resinous substance 

 mentioned, might cause the oxidation of the latter in the 



• Communicated by the Chemical Society j having been read December 

 1, 1845. 



