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A source of error in spectroscopy
12
iNiioriu1.
method
is a simple
ordinarily
one, and certainly
far more
than that
convenient
used.
Railway llication
upon
quantity
the
of the
composition
m:cterinl
in 8 railway
window
vJ;ts. Sidcbotham*
Dust,---Mr.
croscopical
by
of railway
dust;
and subsequently
A
having
spreadin g a newspaper
carriage,
examination.
1~s published
large
collected
near
subjected
proportion
colnmu-
a
a.
an open
it to a mi-.
of the fragments
were
They were mostly long, thin and straight, the largest being about *I50 inch, and had much t,hc appearance of old nails. Of the original q,uantity collected (6’7 grains) one-half of it (29 grains) were removable with the magnet, and cow&tell therefore of iron. to be iron.
found
The bright
other
portion
angular
of the
fragtncnts
dust
consisted
of gl:~ss
largely
or yusrt,z,
of cinder*,
a few
hits
son-w
of yellow
metal, opaque white and spherical bodies, a few bits of coal, etc. The character of it,s constituents affords a satisfactory explanation for the irritating
effects
On the
Estimation
thrciat
produced
of Graphite.-
after
inhaling
2’. Stolbat
the material.
communicates
the
fact
to determine, accurately enough for practical purof carbon in commercial graphite by simple pOses, the percentage combustion in the air. II e employs for this purpose a simple Bunsen burner, and announces that the burning of a few grammes of graphite is by no mcitns so dit%icult as is generally supposed. !rhe author places a weighed portion of the finely powdered and dried material in a platinum crucible, having a punctured cover. The crucible is placed over the flame in >Ln inclined position, and the cover is placed so as t0 lcavc one-fourth of thr: same open, By this arr;lngcment, by whh a good dr?ft is secured within and occasional stirring of the that
it is possible
material,
a few
excellent
condition
hours
A Source of Error an interest.ing of the prism been noticed displacement altering with
completes
for further
the operation,
leaving
the ash in an
;bnalysis.
in Spectroscopy,-!vf.
Blascrns:[ has mado observation upon the infiuencc which the tcrnperature It has already exercises upon the position of the lines. by Vcrdet that where liquids arc used for prisms the of the lines is quite noticeable, the indcs of refraction the temperature. ?+P~oc. Lit. and Phil. Sot., Manchester. t Dingier’s *Journal, cscviii, 213. 1 Pogg. Ann., cxliii, 6%.
items For
solid
prisms,
ami Novelties.
13
however,
it was assumed that the influence of temperature changes upon their refractive power was quite insign& cant. The zuthor has found, however, upon observation, that this is not so unimportant as is generally believed ; but that, while much less sensitive than liquid prisms, the displacement of lines could readily be observed with one of flint glass. The prism used in the experiment was one of Duboscq’s; and was exposed for some time to the direct rays of the sun. It was t,hen quickly placed in a spectroscope in the shade, and some prominent line observed, when it wns found that as the glass cooled the rcfrnctivc power increased. (An opposite result is obtained for bisulpiiide of carbon.) He was enabled to observe in this manner n displaccmcnt of the I) line amounting to 3” for a difference in temperature, equal to 1’ Cent. In the instrument used the interval between 1) and D’ is 12”, so that a change of 4’ C. would sufllce to place D in t,he position of D’. The author remnrks, as the result of his intcrcsting observation, that an error might very readily be made in spectroscopic work by comparing together observations made in sunlight and in shade, or those made in the morning with those in the night.
Passivity of Cadmium.--Dr. Sch6nn announces that the metal cadmium
may, u&r certa,in circumstances, be rendered indifferent to It has long been known that iron, if plunged t.hc action of acids. into this acid of a certain degree of concentration, acquires a peculiar surface condition, rendering it indifferent to the action of the strongest Iron which has undergone this surface change has been termed acid. It appears, too, that such iron has acquired some peculiar passive. physical qualities, since it will form a galvanic circuit with ordinary iron ; the cllanged metal behaving electrically negative to the other. That such iron has really been decidedly a.ltercd in character is evinced again by the fact that, it refuses to reduce copper from solutions of its salts. observation, that if cadmium is It appears, from Dr. Schijnn’s wrapped with some platinum wire, it may be placed, without being in the least acted upon, instrong nitric acid; though if the wire SWrounding is removed, or if the acid is diluted, the cadmium is instantly attacked, thus showing that the passivity of the cadmium is due entirely to its contact with the platinum. The same author has shown’ that tin will give the same phenomenon.
iNiioriu1.
method
is a simple
ordinarily
one, and certainly
far more
than that
convenient
used.
Railway llication
upon
quantity
the
of the
composition
m:cterinl
in 8 railway
window
vJ;ts. Sidcbotham*
Dust,---Mr.
croscopical
by
of railway
dust;
and subsequently
A
having
spreadin g a newspaper
carriage,
examination.
1~s published
large
collected
near
subjected
proportion
colnmu-
a
a.
an open
it to a mi-.
of the fragments
were
They were mostly long, thin and straight, the largest being about *I50 inch, and had much t,hc appearance of old nails. Of the original q,uantity collected (6’7 grains) one-half of it (29 grains) were removable with the magnet, and cow&tell therefore of iron. to be iron.
found
The bright
other
portion
angular
of the
fragtncnts
dust
consisted
of gl:~ss
largely
or yusrt,z,
of cinder*,
a few
hits
son-w
of yellow
metal, opaque white and spherical bodies, a few bits of coal, etc. The character of it,s constituents affords a satisfactory explanation for the irritating
effects
On the
Estimation
thrciat
produced
of Graphite.-
after
inhaling
2’. Stolbat
the material.
communicates
the
fact
to determine, accurately enough for practical purof carbon in commercial graphite by simple pOses, the percentage combustion in the air. II e employs for this purpose a simple Bunsen burner, and announces that the burning of a few grammes of graphite is by no mcitns so dit%icult as is generally supposed. !rhe author places a weighed portion of the finely powdered and dried material in a platinum crucible, having a punctured cover. The crucible is placed over the flame in >Ln inclined position, and the cover is placed so as t0 lcavc one-fourth of thr: same open, By this arr;lngcment, by whh a good dr?ft is secured within and occasional stirring of the that
it is possible
material,
a few
excellent
condition
hours
A Source of Error an interest.ing of the prism been noticed displacement altering with
completes
for further
the operation,
leaving
the ash in an
;bnalysis.
in Spectroscopy,-!vf.
Blascrns:[ has mado observation upon the infiuencc which the tcrnperature It has already exercises upon the position of the lines. by Vcrdet that where liquids arc used for prisms the of the lines is quite noticeable, the indcs of refraction the temperature. ?+P~oc. Lit. and Phil. Sot., Manchester. t Dingier’s *Journal, cscviii, 213. 1 Pogg. Ann., cxliii, 6%.
items For
solid
prisms,
ami Novelties.
13
however,
it was assumed that the influence of temperature changes upon their refractive power was quite insign& cant. The zuthor has found, however, upon observation, that this is not so unimportant as is generally believed ; but that, while much less sensitive than liquid prisms, the displacement of lines could readily be observed with one of flint glass. The prism used in the experiment was one of Duboscq’s; and was exposed for some time to the direct rays of the sun. It was t,hen quickly placed in a spectroscope in the shade, and some prominent line observed, when it wns found that as the glass cooled the rcfrnctivc power increased. (An opposite result is obtained for bisulpiiide of carbon.) He was enabled to observe in this manner n displaccmcnt of the I) line amounting to 3” for a difference in temperature, equal to 1’ Cent. In the instrument used the interval between 1) and D’ is 12”, so that a change of 4’ C. would sufllce to place D in t,he position of D’. The author remnrks, as the result of his intcrcsting observation, that an error might very readily be made in spectroscopic work by comparing together observations made in sunlight and in shade, or those made in the morning with those in the night.
Passivity of Cadmium.--Dr. Sch6nn announces that the metal cadmium
may, u&r certa,in circumstances, be rendered indifferent to It has long been known that iron, if plunged t.hc action of acids. into this acid of a certain degree of concentration, acquires a peculiar surface condition, rendering it indifferent to the action of the strongest Iron which has undergone this surface change has been termed acid. It appears, too, that such iron has acquired some peculiar passive. physical qualities, since it will form a galvanic circuit with ordinary iron ; the cllanged metal behaving electrically negative to the other. That such iron has really been decidedly a.ltercd in character is evinced again by the fact that, it refuses to reduce copper from solutions of its salts. observation, that if cadmium is It appears, from Dr. Schijnn’s wrapped with some platinum wire, it may be placed, without being in the least acted upon, instrong nitric acid; though if the wire SWrounding is removed, or if the acid is diluted, the cadmium is instantly attacked, thus showing that the passivity of the cadmium is due entirely to its contact with the platinum. The same author has shown’ that tin will give the same phenomenon.