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Art. XLIX.—On certain Chemical Effects of Oxygenized Graphite and Platinum.
In the experimental results I am about shortly to describe, I do not for the present distinguish between graphite, etc., as combined with a compound of oxygen such as nitric acid, which easily gives up oxygen, or graphite, etc., as combined with oxygen alone, either as oxygen or ozone.
In some of them it is most probable that this acid or a product of it, as absorbed by the graphite, operates for their production, while in others it really appears that it is oxygen which is the sole operant.
But, as all these experiments were carried on in the presence of nitrogen, a gas which is, as we know, susceptible of being acted upon in certain cases by oxygen in such a manner that nitric or nitrous acids result; and, further, nitric acid is, as I have long since shown, absorbed by charcoal, and also, as will presently appear, by graphite and platinum too, I cannot, therefore, as yet unreservedly attribute any of these results to the action of absorbed oxygen alone, although, as previously stated, I incline to this view.
Having thus defined the position I would hold for the present in regard to the bearing of these results, I will at once state them. They are as follows:—
| 1st. |
That any surface of graphite, native or artificial, which has been for some time exposed to the air, liberates iodine from a solution of potassic iodide in weak sulphuric acid. |
| 2nd. |
That graphite, which can thus liberate iodine, loses this property when washed in ammoniacal or other alkaline solutions; also by ignition. |
| 3rd. |
That this property of liberating iodine is restored to such graphite by a short exposure of it to the air; or by evolving nascent hydrogen against it; also by digesting it for a little while with hydrochloric or weak sulphuric acid, either at a common, temperature, or at the boiling point of these acids respectively. |
| 4th. |
That graphite, which thus liberates iodine, also rapidly determines a chemical effect upon mercury, when voltaically paired |
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with it in pure hydrochloric acid, mercurous chloride forming. |
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| 5. |
That platinum can be substituted for graphite in the above experiments, with the same general results. |
I farther find that charcoal does not, even when freshly prepared, notably liberate iodine; but it can be made to do so by digesting it with an acid, the effect of which is perhaps due to its removing all alkaline matters therefrom, and thus enabling the charcoal to retain the oxidizing agent necessary for effecting the liberation in view.
Silver, also, liberates iodine from the solution of it I have named here, and gold even appears to do this, but to a much less extent.
Nitric acid has the same effect upon either graphite or platinum (in relation to iodine) as exposure to air has, and prolonged washing of these metals afterwards does not in any way interfere with this effect, showing, no doubt, that this acid has been absorbed by these metals and is retained very obstinately.
The graphite I used was of course purified both from iron and manganese before being worked with.
In reference to the chemical action of substances upon which oxygen has been in some way condensed, I may perhaps be allowed to state further that when graphite, which has been exposed to the air, is voltaically connected in sea water with graphite just recently ignited, electric currents are generated; graphite, which has been desulphurised, also generates electric currents when connected in this manner with any negative conducting sulphide in a solution of an alkaline sulphuret. By the use of currents generated in this manner I have even electrolyted copper from its sulphate.
I forbear making any specific deductions from the results above related until I can supplement them in such a way as will enable me to discriminate with greater surety than I at present can, the exact nature of the absorptive process by which graphite and platinum become chemically active in the way these results indicate.