546 Prof. Schoenbein on the Chemical Inactivity of Bismuth, fyc. 



be effected as often as you like. I have ascertained that bis- 

 muth covered with the said blackish coating is more energe- 

 tically acted upon by nitric acid than it is when its surface ap- 

 pears to be bright. Now as platinum, by means of its contact 

 with bismuth, causes a very considerable diminution of the 

 energy of chemical action of the acid upon the latter metal, 

 and makes the black film always and instantaneously disap- 

 pear from it, the reproduction of this coating under the cir- 

 cumstances before mentioned is a fact very strange indeed, and 

 altogether anomalous. Another fact also worthy of being 

 stated is, that the black film can be produced either by moving 

 the bright bismuth about within the acid or by causing the acid 

 to be moved about the metal. I do not yet know what the 

 black substance consists of, but whatever it may be, its produc- 

 tion in the last-mentioned way is no doubt due to the removal 

 of some stratum surrounding the bright metal and protecting 

 the bismuth against the violent action of nitric acid. This 

 supposed stratum consists perhaps of a solution of nitrate of 

 bismuth mixed with some nitrous acid. 



If bismuth being in its peculiar state or covered with theblack- 

 ish film be tightly [strictly ? J touched with a platinum wire within 

 nitric acid of sp. gr. 1*4, a gaseous substance will be disengaged 

 at the wire all the while contact is maintained between the 

 metals. Having not yet made the experiment on a scale large 

 enough to allow the collection of the gas, I do not know its 

 nature. I have stated however the fact to you, because the 

 development of a gaseous body under the circumstances al- 

 luded to must appear very odd, if we consider, that no gas 

 whatsoever is disengaged at the negative electrode when nitric 

 acid of some strength, for instance of sp. gr. 1*4, is sub- 

 jected to the action of the current of a pile. Now in the case 

 spoken of, the platinum wire does certainly act the part of 

 the negative electrode. As every circumstance connected with 

 the peculiar condition of readily oxidable metals appears to me 

 to be of some importance, I will not omit to mention the fact, 

 that inactive iron cannot be brought into contact with inactive 

 bismuth without being thrown into chemical action. Iron, 

 however voltaically associated with platinum, is proof to the 

 exciting influence of the passive bismuth, and capable of de- 

 stroying the often-mentioned black substance Justin the same 

 manner as platinum. Some few words more on the peculiar 

 state of bismuth and I have done with this subject, with which 

 I am afraid I have already occupied you too long. By im- 

 mersing that metal for a few seconds into nitrous acid it is 

 turned inactive, so that it can be put into nitric acid of sp. gr. 

 1*4 without being sensibly attacked by the latter. 



