; , ; ; : CHEMICAL
Volumetric Determination of Binoxide of Manganese. {C¥3uican Naws,
the box, and could be warmed with a spirit-lamp. The ' dust-free line would form itself. I have tried this experi.
dark plane was well developed. At a moderate distance ment, but looking along the axis through the glass top of
above the blade it is narrow, sometimes so narrow as :he vessel I could see no sign of a dark line, so long as
almost to render necessary a magnifying glass ; but below, the rotation was uniform. When, however, the vessel
where it attaches itself to the blade, it widens out to the was stopped, a column of comparatively smoke-free air
full width, as shown in the figure. Whether the heated ieveloped itself along the axis. This I attributed to the
body be a thin blade or a cylindrical rod, the fluid passes formation of an inward flow along the top of the vessel,
round the obstacle according to the ele&rical law of flow, combined with a downward flow along the axis after the
the stream-lines in the rear of the obstacle being of the manner describedand explained by Professor James Thomsame
 form as in front of it. This peculiarity of behaviour son, so that the purified air had been in intimate proxis
 due to the origin of the motion being at the obstacle imity with the solid cover. It would almost seem as if
itself, especially at its hinder surface, If a stream be this kind of contac was sufficient to purify the air without
formed by other means, and impinge upon the same the aid of centrifugal force.
obstacles without a difference of temperature, the motion The experiments made hitherto in order to elucidate
is of a different character altogether, and eddies are formed this portion have given no decisive result. If the thin
in the shadow. convex blade already spoken of be held in the smoke-box
The difference of temperature necessary to initiate in a vertical instead of in a horizontal plane, the lines of
these motions with this dark plane accompaniment is in- motion are much less curved, and we might expe to
significant. On July 20, 1881, a glass rod, about }-inch :liminate the influence of centrifugal force. I have not
in diameter, was employed. It was heated in a spirit- succeeded in this way in getting rid of the dark plane;
lamp, and then inserted in the smoke-box. The dark but since under the magnifier the curvature of the motion
plane gradually became thinner as the rod cooled, but was still quite apparent, no absolute conclusion can be
could be followed with a magnifier for a long time. While drawn.
it was still quite distin& the experiment was stopped, and
an opening the box the glass rod was found to be scarcely
warmer than the fingers. It was almost impossible to
believe that the smoking matter had been evaporated.
In order to test the matter more closely, smoke was
slowly forced through a glass tube heated near the end
pretty strongly by a spirit-lamp, and then allowed to
emerge into the concentrated sunshine. No distin@
attenuation of the smoke could be detetted even under
this treatment,
It is not necessary to dwell further upon these considerations,
 as the question may be regarded as settled by
a decisive experiment tried a few days later. The glass
rod before use was cooled in a mixture of salt and ice,
and after wiping was placed in the box. Ina short time a
dark plane, extending downwards from the rod, clearly
developed itself and persisted for a long while. This
result not merely shows that the dark plane is not due to
gvaporation, but also excludes any explanation depending
apon an augmentation in the difference of densities of
uid and foreign matter.
The experiment was varied by using a |J-tube, through
which cooled water could be made to flow. When the
water was not very cold, the appearances were much the
same as with the solid rod ; but when, by means of salt
and ice, the tube was cooled still further, a curious complication
 presented itself. Along the borders of the dark
plane the smoke appeared considerably brighter than elsewhere.
 Sometimes when the flow was not very regular it
looked at first as if the dark plane had been replaced by a
bright one, but on closer examination the dark plane could
be dete@ted inside. There seems no doubt but that the
effect is caused by condensation of moisture upon the
smoke, due to the chilling which the damp air undergoes
in passing close to the cold obstacle. Where the fog
forms more light is scattered, hence the increased bright.
ness, That the fog should not form within the smoke.
free plane itself is what we might expe& from the interest.
ing observations of Aitken.
With respeét to the cause of the formation of the dark
plane, the most natural view would seem to be that the
relatively dense particles are thrown outwards by centrifugal
 force as the mixture flows in curved lines round the
obstacle. Even when the fluid is at rest, a gradual subsidence
 must take place under the a@ion of gravity ; but
this effe@ could at first only manifest itself at the top
where the upper boundary of the gas prevents the entrance
of more dust from above. It is known that air in a closed
space will gradually free itself from dust, but the observation
 of a thin dust-free stratum at the top of the vessel is
lifficu’t. If we conceive a vessel full of dusty air to be
set into rapid rotation, the dust might be expe&ed to pass
outwards in all dire&ions from the axis, along which a

THis communication contains the results of an inquiry
nade to determine the constitution of the heptane which
ne of them found in the resinous exudation from Pinus
Sabiniana. The pure heptane was converted into a
mixture of chlorides, and these were transformed into the
:orrespoding primary and secondary alcohols. The
cohol was then oxidised, and from the analysis of the
silver salts it was proved that Pinus heptane had yielded
primary heptyl alcohol and methyl-pentyl-carbinol,
:xa@ly as in the case of heptane from petroleum.
A second portion of the chlorides was converted into
aeptylene, boiling at 985°, which, unlike the heptylene of
analogous constitution, combines only slowly with hydrochloric
 acid. The heptylene by oxidation was shown to
se butyl-methyl-ethylene, C;HyCH=CH.CHj; it had been
‘ormed from the secondary heptyl chloride—
C4 Hy—CH,—CHCLCHj;.
The results of the investigation afford further evidence
of the fact that when chlorine ads upon a normal paraffin,
not all the chlorides indicated by theory are formed, but
only the primary chloride, and a secondaty chloride, which
contains the group—CHCI.CH,.

THE basis of this process consists in heating the sample
containing the binoxide with an excess of a solution
of stannous chloride and some hydrochloric acid, the follow-‘ng
 reaction taking place :—
t.—MnO; + 8nCl; + 4HCl=SnCl, + MnCl, + 2H,0.
By now adding ferric chloride in excess, all the excess
of stannous is oxidised to stannic chloride, a correspondng
 amount of ferrous chloride being formed thus :—
2.—8nCl,+ Fe,Clg= SnCl + 2FeCl,.
The iron thus deoxidised is then estimated by a stanlard
 solution of potassium bichromate,
P Abstra& of a Paper read before the Royal Society, Dec, 21. 1882.