Su
'2) 50 c.c. filtrate from
the gelatine .. .
25 cc. indigo so- consumed II'2C.c. permanganate.
lution ox wef
Ditto repeated ..

Ejfects of Oxygenised Graphite and Platinum. JEnaen Nans,
ON CERTAIN CHEMICAL EFFECTS OF
OXYGENISED GRAPHITE AND PLATINUM."
By WILLIAM SKEY,
Analyst to the Geological Survey of New Zealand.

Co. 22°3 4
50 c.c. indigo alone en ee 13°24,

”

Gallic acid and impurities .. g1 ,, »
Now, deducting g'1 c.c. from 1g°g c.c., we have 108 c.c.
is the permanganate equivalent to the tannin of 20 c.c. of
sumach infusion, or 0'2 grm. of dry sumach. If it be
desired to compare two sumachs, these proportional numbers
 are all that is necessary, and indeed it will be quite
safe to use them for comparing sumach with galls or pure
:annin. In the same way bark may be compared with
nark, and valonia with valonia, but it will not be safe to
attempt by this means to compare bark with sumach or
with valonia, because the different species of tannin conscme
 different proportions of permanganate. Oser states
that 14 grms. of oak-bark tannin consumes only the same
juantity as 1 grm. of gall-nut tannin.
I may remark that where many analyses have to be
performed the constant stirring becomes very tedious, and
a stream of air-bubbles forced through the liquid by an
aspirator may be substituted with great advantage.
Neubauer reckons 1 litre of decinormal permanganate
as equal to 4157 grms. of gallotannic acid, and consequently
 (according to Oser) to 6235 of oak-bark tannin.
Further research, however, is needed before percentages
2an be calculated with certainty, and chemists, in giving
results, would do well to state the equivalent in permanganate,
 or to say that they use Neubauer's or Oser's
equivalent. The first is applicable to sumach, galls, and
myrabolans ; the second probably to oak-bark, valonia,
and chestnut extrac, at least approximately, It is a singular
 fa that gallic acid consumes not only a larger
proportion of permanganate, weight for weight, than
1annin, but even a larger proportion than the tannin from
which it is derived, as I proved by digesting a solution of
:annin with dilute sulphuric acid, when its reducing power
vas notably increased. Hence commercial tannin, which
® largely contaminated with gallic acid, consumes more
permanganate than the above-mentioned quantity.
As to accuracy, single tests should never differ by more
than o°1 c.c., or say 2} per cent of the total quantity ; but
of course, in so rapid a process, no one would rely on
single tests, and by repeating and taking the mean any
required accuracy may be attained. Separate portions of
liquor precipitated by gelatine give identical results, at
least within the limits named.
I should perhaps mention that Mr. Estcourt proposed
some time since to precipitate with gelatine in conjunction
with the permanganate method (CHEM. NEWS, vol. xxix.,
n. 110), but as he heated the solution, and tannate of
gelatine is soluble in hot gelatine solution, the results were
not satisfactory. Still he undoubtedly deserves the credit
of the idea, while Lowenthal's cold gelatine solution, with
the addition of salt and acid. completely overcomes the
difficulty.
Several other oxidising methods have been proposed.
Carpeni precipitates the tannin with ammonio-acetate of
ring, re-dissolves and estimates with permanganate. M.
Jean oxidises with iodine in solution of sodic carbonate,
and M. Pouchet with concentrated permanganate in a
caustic potash solution. None of these methods seem to
have any advantage over L.owenthal's, while the two latter
are in my experience decidedly inferior. The end-rea&ions
are much lesa distin@, and it is quite impossible to work
them by artificial light, which is almost preferable with
the indigo process, and is often a great convenience.
In speaking of the results I have obtained as a test of
the accuracy of methods, I do not mean to convey that they
are the best attainable, but simply such as would be likely to
be obtained by a chemist of average skill and experience.

[N the experimental results I am about shortly to describe
[ do not for the present distinguish between graphite, &c.,
1s combined with a compound of oxygen such as nitric
icid, which easily gives up oxygen, or graphite, &c., as
:ombined with oxygen alone, either as oxygen or ozone.
[n some of them it is most probable that this acid, or a
sroduct of it, as absorbed by the graphite, operates for
heir production, while in others it really appears that it
8 oxygen which is the sole operant.
But as all these experiments were carried on in the
resence of nitrogen, a gas which is, as we know, suscepible
 of being acted upon in certain cases by oxygen in
such a manner that nitric or nitrous acids result,—and,
urther, as nitric acid is, as I have long since shown, absorbed
 by charcoal, and also, as will presently appear, by
jraphite and platinum too,—I cannot therefore as yet un-‘eservedly
 attribute any of these results to the action of
ibsorbed oxygen alone, although, as previously stated, I
ncline 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: —

1. 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.
[hat graphite, which can thus liberate iodine, loses
this property when washed in ammoniacal or other
alkaline solutions ; also by ignition.
Chat 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 tem.
perature or at the boiling-puint of these acids
respectively.
That graphite, which thus liberates iodine, also rapidly
 determines a chemical effe@ upon mercury,
when voltaically paired with it in pure hydrochloric
acid, mercurous chloride forming.
[hat platinum can be substituted for graphite in the
above experiments, with the same general results.

1 further find that charcoal does not, even when freshly
srepared, notably liberate iodine ; but it can be made to
lo so by digesting it with an acid, the effe& of which is
serhaps due to its removing all alkaline matters theretom,
 and thus enabling the charcoal to retain the oxidising
gent necessary for effecting the liberation in view.
Silver, also, liberates iodine from the solution of it I
1ave named here, and gold even appears to do this, but to
1 much less extent.
Nitric acid has the same effe® upon either graphite or
>latinum (in relation to iodine) as exposure to air has, and
srolonged washing of these metals afterwards does not in
\ny way interfere with this effe@, showing, no doubt, that
‘his acid has been absorbed by these metals and is retained
rery obstinately.
The graphite I used was of course purified both from
ron and manganese before being worked with.
In reference to the chemical action of substances upon
vhich oxygen has been in some way condensed, I may
verhaps be allowed to state further that when graphite,
which has been exposed to the air, is voltaically connected
n sea water with graphite just recently ignited, eleé&rc

Read before the Wellington Philosophical Society. lanuarv 29,
yh