Ca Nene} Estimation of Chromium in Iron and Steel, 285
TS —p——  S—— TE; TT —— ee ee
gently boiled till the fused mass is detached and dissolved
TH E C H E M I C A L N E Ww S out. This may be assisted by occasional stirring with a
* glass rod. When clear from oxide, remove the crucible and
cover, washing them well with hot water. Add 3 or
t drops of alcohol to decompose the manganate, and allow
:he oxides of Fe and Mn to settle thoroughly. When the
supernatant liquid is quite clear it is decanted on a close
double filter, the filtrate being received into a clean beaker.
The precipitates are disturbed as little as possible. When
ill the clear liquid has passed through, the filter is well
washed with hot water. The precipitates are now washed
twice by decantation with 30 c.c. of hot water ; at the
second washing the contents of the beaker are allowed to
drain gently into the filter, which is now allowed
to drain thorcughly, and is removed without further
washing. These precautions in washing must be strily
carried out, as the Fe,0y is in such an exceedingly fine
state of division that any attempt to wash or disturb it on
the filter will inevitably cause some of it to pass through
into the chromium solution. The clear yellow filtrate
contains the Cr and Si; to it is added 20 c.c. of HCI, the
cover being kept on the beaker, to prevent projection of
ihe solution by the evolved CO,. The solution is now
well boiled until all the CO, and nitrous funies are driven
off. Its colour will now be green owing to reduction to
chloride. Dilute AmHO is added to alkaline readion and
the solution heated nearly to boiling. The resulting precipitate
 consists of Cra(HO),Si(HO),, mixed with alkaline
salts, It is colleted on a filter (previously well washed
with hot dilute HCI to free it from iron), and is slightly
washed. When the washings have drained through, the
precipitate is dissolved off the filter with hot dilute HCI,
the filtrate being received into the beaker in which the
precipitation took place. The solution is now evaporated
‘0 dryness to convert the Si(HO), into Si0;. The soluble
Cr;Clg is taken up with 10 c.c. HCI and go c.c, of water,
and is filtered through a washed filter into a clean beaker,
the filter being well washed, The precipitation is now
repeated as above, and the Cr,(HO)s comes down free
from silica and alkaline salts. It is collected, washed,
dried, ignited, and weighed as Cr;0a.
Precautions,—Only 3 or 4 drops of alcohol should be
added, as this quantity is sufficient, not only to precipitate
 the manganese, but also to effe@ the reduction to
chloride. If too much is added organic compounds are
iormed, which tend to prevent the complete precipitation
of the hydrate. The ammonia in the last precipitation
should be added in the least possible excess, and the solu.
tion should be heated gently nearly to boiling. If any
great excess of ammonia be present, and if the solution is
boiled, the glass of the beaker is attacked and the result
is high. ‘The method if carefully carried out is accurate,
as the following analyses will show :—
Three quantities of a steel free. from chromium, each
weighing 198 grms., were taken; to each was added
0'0563 grm. K,Cr;0,. This mixture corresponds to a
steel containing 1 per cent Cr.
A gave 0973 per cent chromium.
B ,, 1022 , »
Cc 0978 » I
Mean, 0'9gx per cent.
Three quantities weighing 1°99 grms, were now taken,
and 002815 grm. pure K,Cr,0, was added to each. This
mixture corresponds to a steel containing o's per cent Cr,
A’ gave o'511 per cent Cr.
B' ,, oy470 » »
C' 4 0508 ” ”
Mean, 0496 per cent.
The results B, A’, C', are high, owing to boiling off
excess of ammoniz. I believe the error to average 0°03
per cent low, as a third series corresponding to 1 per cent
Cr gave, when excess of ammonia and boiling were
avoided +—

Tris subje® has received comparatively little attention
from iron and steel chemists, and, as far as I know, no
satisfactory method has yet been published. The method
in general use is volumetric and indire®. The steel is
dissolved in dilute H,SO,, the Cr;(80,); thus formed is
oxidised to H,CrO4 by means of KMnO,. The solution
is filtered, acidified, and a known weight (in excess) of
FeSO, is added. The excess is determined by a standard
solution of K,Cr,0,. The difference between the original
amount and the excess is the amount of Fe converted
from the dyad to the tetrad condition by the chromic acid.
From this the Cris estimated; every 3 equivs. Fe represent
 1 equiv. Cr,
This method I find to be most unsatisfa&ory, In the first
place, the results depend upon a ferrous solution, liable at
any moment to accidental oxidation, and from this cause
alone, when experimenting with steels into which a known
amount of Cr had been intreduced, I have observed errors
ranging from 0'05 to 0'2 per cent. But in the actual alloy
a constant cause of error arises from the fa& that chrome.
steel is not completely soluble in dilute H.SOy, even after
long-continued boiling. A black residue remains, consisting
 of Fe, Mn, and Cr. If this residue is thoroughly
washed with hot water, dried, and fused with Na,COj, the
mass dissolved out with hot water, a drop of alcohol
added, and the solution filtered, the yellow colour of the
chromate will be seen; it may be reduced with HCl, ammonia
 added, and a distin& precipitate of Crz(HO)g obtained.
 In the case of a soft steel that cannot be crushed
to a fine powder, the error becomes most serious. I would
therefore propose the following dire& and gravimetric
method :—
Weigh out from 1 to 5 grms. of the steel (in drillings)
according to the amount of Cr present (this may be ascertained
 by a rough colorimetric test), Place the metal in
a wide, covered beaker, and add 20 c.c. of strong HCl;
heat till all action is at an end; rinse the cover and sides
of tte beaker from splashings, and evaporate the solution
gently to complete: dryness. If the evaporation has not
been too rapid, the chlorides may be almost entirely detached
 from the bottom of the beaker in a brittle cake.
This is broken up into small pieces by means of a platinum
spatula, and as much as possible is brushed out into a
clean dry porcelain dish. A small quantity of the chlo.
rides will, however, remain adhering to the beaker; this
may be removed with 2 or 3 c.c. of dilute HCl. The solu.
tion is poured into a deep platinum crucible, the beaker
rinsed with 1 or 2 c.c. of water, the washings added to the
crucible, the contents of which are now evaporated to dryness
 on a sand-bath. When dry the main quantity of the
chlorides is carefully brushed ‘out of the porcelain into
the platinum dish, and is reduced to a fine powder by
means of a little pestle made from glass rod. The
spatula and pestle are cleaned into the crucible. The
finely-divided chlorides are now thoroughly mixed with an
excess of fusion mixture (x part dry Na,COj to 1 part
powdered KNOg), a cover is placed over the crucible, and
its contents are fused over a gas blowpipe till quite liquid,
By this treatment the Fe is converted into insoluble oxide,
the Mn, Si, and Cr respecively into alkaline manganate,
silicate, and chrothate, When cool the crucible is placed
in a beaker containing 80 c.c. of boiling water, and is