J. A. (Joseph Allen) Pickard.

Modern steel analysis; a selection of practical methods for the chemical analysis of steel online

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Online LibraryJ. A. (Joseph Allen) PickardModern steel analysis; a selection of practical methods for the chemical analysis of steel → online text (page 1 of 7)
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J. A. P I C K A R D

B.Sc. (Hons. Lond.), A.R.C.Sc., A.I.C.

Carnegie Research Scholar of the Iron and Steel

Institute, Fellow of the Chemical

Society of London




Printed in Great Britain


IN writing the present book it has been the endeavour
of the author to condense into a small space practical
methods for the exact estimation of all those con-
stituents of steel which are of fairly common occurrence.
It is hoped that the book will be found useful by steel
analysts who do not possess either the time or the
facilities for personally sifting the mass of literature
which is annually published on the subject, and that
it will also meet the requirements of third and fourth
year students who, after a general training in chemistry,
are desirous of obtaining some practical experience in
analysis which is commercially important. No attempt
has been made to give a comprehensive description of
all the processes used in the analysis of steel, but the
methods detailed have been selected for their practical
utility. A section on general procedure has been
included primarily to meet the needs of students'with-
out experience in chemical practice, but it is hoped that
some of the hints contained therein may also be of
service to other chemists.

Methods for the estimation of tantalum, columbium,
tin, boron, and a few other unusual constituents of


steel have not been included in the present volume, but
should this little work prove useful to chemists it is
hoped to include them in a subsequent edition.

The author desires to express his indebtedness to
Messrs. C. H. and N. D. Ridsdale, of Middlesbrough, for
permission to publish details of their well-known
mechanicalized methods.

J. A. P.































THE following remarks are intended primarily to guide
students who have pursued a general course of training
but are without practical experience of procedure in a
routine laboratory. Chemists daily engaged in analysis
may consider many of the statements obvious or un-
necessary, but it is the author's experience that students
who have attained a sound theoretical knowledge are
frequently lacking in the ability to perform operations
in the simplest way necessary to ensure accuracy.
Analytical chemistry as taught in many colleges is,
to a large extent, far too academic in its quality : pre-
cautions are insisted upon, but no account is taken of
their relative value. For example, before weighing an
ignited precipitate of barium sulphate the addition of
a drop of nitric acid followed by a drop of sulphuric
acid to convert any sulphide formed by reduction by
the filter ash back into sulphate and re-ignition is
always insisted on, but the complete insolubility of
barium sulphate, however precipitated and however
washed, is a matter of faith. With proper ignition the
error introduced by neglect of the former precaution
can hardly exceed 5 per cent, of the weight of the
precipitate in the most extreme cases, whereas if the
precipitate be not obtained by adding the barium
chloride solution slowly to the boiling sulphate solution


only 60 to 70 per cent, of the barium sulphate may be
precipitated from dilute solutions in twelve hours, and
if the precipitate is washed with dilute hydrochloric acid
the greater part will be dissolved from off the filter
again. Again, rapidity is hardly considered, nor is
there any attempt to avoid the performance of un-
necessarily laborious operations. For instance, a sample
is weighed out by difference weighings from a weighing
bottle, which establishes the weight taken accurately
to about 1 in 50,000, while duplicate determinations will
not agree to the third significant figure.

Weighing. Analysts are chiefly concerned with the
weighing of the amount of sample taken, the final
ignited precipitate, and absorption tubes.

Weighing out Sample. It is usually found desirable
in practice to adjust the weight of the sample to an
even number of grams, or to a convenient factor weight ;
as this simplifies calculations, reduces the number of
notes to be made, and minimizes the liability to errors
in weighing. This is most readily managed by using
a small scoop, hammered or stamped out of aluminium
or other sheet metal, exactly counterpoised by a suitably
adjusted lump of metal placed in the pan carrying the
weights. After weighing, the sample is tipped out of
the scoop into the beaker or flask, and if necessary the
scoop is brushed out with a fine camel-hair brush, but
usually a smart tap will remove everything. In most
analyses it is unnecessary to weigh the amount taken
more accurately than to a milligram, although the moral
effect of the fourth place is sometimes stimulating.

Precipitates. A good many precipitates, such as
silica, barium sulphate, aluminium oxide, are most con-


veniently weighed by brushing out of the crucible into
the balance scoop, taking precautions against loss by
performing the operation over a sheet of smooth paper.
In the case of powdery, non-hygroscopic precipitates
this procedure is to be recommended not only on the
grounds of speed and convenience, but also for its
accuracy, as the chemist is thereby freed from any
doubt as to the fluctuation in weight of the crucible
and is certain that the weight obtained is that of the
precipitate. Not all precipitates, however, can be
brushed out in this manner, and in these cases the usual
weighing in tared crucibles is necessary. Very hygro-
scopic precipitates, which are rare, may be weighed, if
the greatest accuracy is desired, in crucibles enclosed in
stoppered weighing bottles ; but usually it is sufficient
first to adjust the weights roughly, and then to place
the crucible in the pan and complete the weighing as
quickly as possible.

Absorption Tubes. The weighing of absorption tubes
calls for no special mention. They should expose as
small a surface as possible and should be polished with
a soft leather before weighing. After polishing, for the
greatest accuracy they should be left in the balance
case for ten minutes and then weighed ; neglect of this
precaution may lead to an error of as much as two
milligrams. Geissler potash bulbs and other fragile and
intricate apparatus are quite unsuitable for practical use.

Precipitation. To obtain precipitates in such a con-
dition that they filter readily, that is to say in moderately
large and compact particles, is one of the operations in
which the value of practical extended experience is
inestimable. The conditions governing the formation


of proper precipitates follow no general rule, but vary
from case to case. Lead molybdate and cobalt am-
monium phosphate are practically unalterable unless
the liquid in which they are precipitated is well boiled.
In the basic acetate precipitation of iron the liquid
must be raised to boiling-point, but if boiled the pre-
cipitate becomes slimy. Cuprous thiocyanate is most
satisfactory if precipitated from cold solutions after
vigorous stirring, while magnesium ammonium phos-
phate must be precipitated from thoroughly cold
solutions which are well stirred or shaken. In some
cases large excesses of precipitant are desirable, in others
the smallest possible excess. No general rule can be
formulated and knowledge of conditions necessary is
only to be gained by experience ; for although it may be
possible in each case to define exactly the precautions
to be taken it is undesirable to burden a description with
small details which are commonplaces to the man of

Filtration. This operation, which by faulty mani-
pulation may easily occupy more time than all the
other operations of analysis together, when performed
with skill is one of the most rapid. A volume of 300 c.c.
should pass through in five minutes or less, and the rate
of flow should be but little retarded when the precipitate
has been transferred to the filter. Generally speaking,
warm solutions filter better than cold, and acid solutions
better than alkaline, but the most important point is
the proper arrangement of the filtering medium. When
using filter papers, funnels with deep ribs or flutings on
their inside conical surface are much to be preferred to
plain funnels. Plain funnels, even with a well-fitting


filter paper, in addition to filtering rather slowly some-
times allow fine-grained precipitates which go through
the paper to be retained between the glass and the
surface of the paper, with the result that when the filter
paper is removed for ignition some of the precipitate
sticks to the glass and is then rather difficult to transfer
to the crucible ; or it may even be overlooked and lost.
Pulp Filtration. Filters of almost any degree of
openness or fineness may be obtained by the use of
filter-paper pulp, and for a given efficiency
of separation filtration through pulp is
quicker than through folded papers. A
pulp filter is prepared in the following
manner : A number of filter papers are
torn (not cut) into small pieces about half
an inch square or less and placed in a large
flask about half filled with water, preferably FlG - *
hot. The flask is then stoppered and the
contents thoroughly shaken until the filter paper is
completely broken up into shreds. On the score of
cheapness filter-paper clippings are to be recommended
and serve equally well. The filter pad is now prepared
by placing a perforated porcelain filter disc in the neck
of a plain funnel (see Fig. 1), whose stem has been cut
off square but not unduly shortened. Water is poured
in to cover the disc, and pulp suspension added in
sufficient amount, keeping the stem closed meanwhile
with the finger. The filter plate is adjusted in the neck
of the funnel with a glass rod and the finger removed,
when the pulp sinks down and forms a pad. This is
now consolidated by judicious pressure with a flat-
ended glass rod, more or less pressure being used according


to the fineness of the precipitate to be separated. The
edges of the pad are conveniently tucked in by swirling
a fairly rapid stream of water from a wash bottle cir-
cumferentially over it. With such a pad even a sulphur
suspension may be filtered out ; while the rapidity of
filtration is very satisfactory, and the washing of the
precipitate greatly simplified because all the washing
liquid passes through the precipitate and there are no
filter-paper edges to be carefully washed. A filter
pump may be used in conjunction with these pads
without fear of sucking through, but attempted accelera-
tion with a pump in most cases produces only a
temporary acceleration, as with other filters, the last
state being worse than the first.

Filtration through Asbestos. Many liquids which can-
not be filtered through filter paper, such as permanganate
and caustic solutions, may be filtered through ignited
asbestos. Ordinary asbestos is ignited in a muffle and
made up into a suspension with water in the same way
as pulp, and a filter prepared in the way just mentioned.
Special filtering asbestos can be obtained, but is much
more expensive than the ordinary variety and little
better. It is not advisable to use asbestos in filtration
of acid liquids where contamination with metallic salts,
particularly those of iron, aluminium, and magnesium, is
prejudicial, as although an improvement may be made
by extracting with strong hot hydrochloric acid it is prac-
tically impossible to extract everything soluble in acids.
Cotton-wool Filtration. Cotton-wool may be made
use of very advantageously for certain filtrations, as it
is practically ashless and withstands the action of con-
centrated hydrochloric acid, 1*2 nitric acid, and fairly


strong sulphuric acid very well. A cotton-wool filter
is very conveniently made by pushing a pad of cotton-
wool about | in. long into a long tube of J in. bore
supported in a burette stand. This method of filtration
is particularly useful in the estimation of graphite in
pig-iron, as after filtration and washing are complete
the pad is pushed backwards out of the tube, thereby
efficiently cleaning the walls, and may be burnt off at
the mouth of the muffle ; the residual graphite being
then weighed.

Evaporation and Baking. These operations are
performed on a hot plate, which may be conveniently
constructed of a sheet of steel J in. thick, measuring
about 2 ft. by 18 in. The plate may be supported on
iron legs or on bricks, and should have burners disposed
beneath it so that a range of temperature is obtained
from the highest temperatures directly over the burner,
which should impinge on the lower surface, to the com-
paratively cool corners most distant from the flame. A
large spreading flame particularly suitable for heating
hot plates may be obtained by using an ordinary bunsen
burner whose jet has been replaced by a hole J in. in
diameter. Evaporations can be speedily carried out on
a hot plate as the beaker can be placed on a part only
just cool enough to avoid spitting. When evaporated
to complete dryness, Jena beakers may be placed on the
hottest part of the plate and thoroughly baked without
the least danger of cracking the glass if not too suddenly
cooled when removed. It is sometimes convenient to
cover part of the plate with a sheet of asbestos on
which beakers requiring a long digestion at a moderate
temperature may be placed.


Absolute Value of Results. Where there is any
doubt whether a figure obtained as a result of an analysis
actually represents the true percentage of the con-
stituent in the sample, the most satisfactory confirma-
tion of its accuracy is obtained by going through the
same series of operations using a similar solution of
known composition. This is nearly always possible,
and many procedures giving rise to results which would
be erroneous if taken at their face value especially in
volumetric estimations may be made to yield satis-
factory figures by taking into account the behaviour
of the standard or the blank determination. The
standard solution should always be of as nearly as
possible identical composition, not only as to the con-
stituent under consideration and iron, but also as to
the other components of the solution, dilution, acidity,
&c. Often the most satisfactory way is to add a definite
further amount of the doubtful constituent to the
sample, carry through the analysis as before, and see
whether the increased percentage found corresponds to
the amount added, though this is not satisfactory in all
cases. By this means a greater feeling of certainty as
to the meaning of the result is obtained, Lnd the personal
equation, a very important factor in the past, can be

Arrangement of Work. This is perhaps the most
important thing to be learnt by an analyst when once
he has mastered the elements of the science. The dove-
tailing of operations so that the worker's time can be
fully used to the best advantage needs experience and
forethought. A little time is well spent at the beginning
of each day in taking stock of the things to be done and


arranging in what order to do them. There is then no
fear either of time being wasted or of overcrowding any
part of the day with too many operations, conditions
which almost invariably lead to imperfect work and
want of accuracy. It is perhaps hardly necessary to
indicate that long evaporations should be started as
soon as possible, and that while they are proceeding
the shorter estimations may be carried out. Filtration
should be arranged to fall in batches, so that the
operator's time may be fully occupied ; for it takes
but little longer to filter six solutions than one if done
together, though separately they would occupy six
times as long. Economy of time and gas is ensured by
arranging that the precipitates to be ignited are all
burnt off at the same time ; and it takes less time to
make twenty weighings one after the other than it does
to make twenty weighings separately.

Sampling. In taking samples from specimens of
steel the object usually in view is to obtain a repre-
sentative portion of the material in a shape suitable for
analysis ; but sometimes when want of homogeneity, or
segregation, is suspected, sampling is performed with
the intention of revealing this variation in composition.
Since solidification begins from the outer surface of a
casting and the impurities in the steel are both lighter
and more fluid than the pure metal, it follows that the
higher parts of the thickest portions of the casting will
tend to contain a higher proportion of these impurities,
and this fact should be borne in mind when looking for
local variations.

When a representative sample only is needed material
from near the surface should be avoided, particularly


if much re-heating has been performed on the specimen,
as a considerable amount of carbon may have been lost
under these conditions.

The method of taking the sample calls for a little
notice. The usual practice is to drill the sample, using
as large a drill as the sample will take and the power
available permits, since a drill is the most economical
tool for reducing a portion of the specimen to a handy
size for manipulation in view of its requiring least
power for removing a given weight of metal. Turning
is also a permissible method, but filing and milling
are not satisfactory filing because the file teeth are
worn away and contaminate the sample, and milling
because of the great difficulty in cleaning the cutter and
the trouble and expense which would be necessitated by
the frequent grinding and resetting. Whichever method
is employed the tool used should be sharp and used
without lubricant, as it is essential to avoid studiously
any contamination with carbonaceous material.

The following list contains brief instructions for
suitably drilling commonly occurring shapes.

Bars. Drill transversely from side to side, neglecting
drillings from surface.

Plates. Drill through in several places.

Ingots. Drill well in. Always avoid outside layers
and top of ingot.

Rails. Drill parallel with the length in several places.
Carbon may vary from point to point, and the
samples should be kept separate and examined
for carbon segregation. The other determinations
should be carried out in the sample from the
thickest part.


Carriage Springs. Chop off and drill ends trans-

Sample Ingots. Drill from face to face.

Castings. These are so varied in shape that no
general instructions can be given except to avoid
the outside and top parts.

Useful Apparatus. There are a good many simple
pieces of apparatus easily made by any good carpenter

FIG. 2.

which greatly add to the convenience of working and
minimize loss of time. A good draining board, a
measure rack, a beaker rack, and a filtering stand are
really invaluable, and the forms shown in the illustra-
tions have been found quite satisfactory.

Draining Board. This piece of apparatus is too well
known to need much description. It should consist
of a sloping board with vertical pegs to support the
apparatus while drying, and should be of fair size and
be conveniently disposed to drain into the sink.

Measure Rack. A suitable rack may be made by



cutting a number of bays with straight sides, and of
widths adapted to the measures, in a shelf. The
measures are suspended in the bays by means of the
flanges at the bottom and hang mouth downwards, so
that they drain dry and dust does not settle in them.
If a special small shelf is made for them, it should either
be of stout wood or of two-ply material so as to avoid
warping. A drip board may be placed below.


FIG. 3.

Beaker Rack. This consists of a number of slats of
wood arranged to form V-shaped troughs open at the
bottom, and with one side wider than the other. The
wider side of the trough is arranged at an angle of about
30 with the horizontal, the shorter side being at right
angles with the other. The beakers rest in the troughs


with their sides on the wider side of the trough and the rim
against the other side. In this way they drain dry and
dust does not collect in them. A hundred beakers can
easily be kept on a wall-space measuring 4 ft. by 4 ft.,
and any one is instantly available for use.



> <

> <


FIG. 4.

Rack for Flasks. Flasks are conveniently stored in a
rack consisting of two battens or rods of wood arranged
parallel to one another at such a distance apart that
the neck of the flask passes between them and the
flask hangs supported by its sides.


FIG. 5.

Filtering Stand. A stand to take six funnels side by
side, as shown in the sketch, is very handy. It should


have a movable shelf below the funnel stems so that
filtration into beakers of different depths can be carried

Burette Stand. Burettes are very conveniently sup-
ported in the apparatus shown, which consists of two

FIG. 6.

narrow shelves, the lower about 10 in. and the other
2 ft. above the bench level. The lower shelf has notches
a little wider than the burettes cut in it, the upper, holes
through which the tops of the burettes pass. The
burettes are prevented from dropping down by a stout
piece of rubber sheet slipped over them as shown : a
cork will serve equally well.


ALUMINIUM is occasionally present in steels derived
from the ore from which the pig-iron was smelted, but
its presence is more frequently due to the addition of
aluminium in the ladle. It is chiefly important in view
of its action in producing quiet casts, which effect is
supposed to be due to its rapid reduction of the oxides
present without elimination of gas.

In the estimation of aluminium in steel advantage is
usually taken of the insolubility of aluminium phos-
phate in neutral solutions, ferrous phosphate being
soluble. The estimation of very small amounts of
aluminium with accuracy is attended with some
difficulty, but fortunately the importance of traces of
this element is generally considered to be small.

Estimation. Dissolve 10 or 20 grm. of the sample
in 100 or 200 c.c. of hydrochloric acid (1 : 1). Boil the
solution, dilute to 300 c.c. and pass H 2 S until the pre-
cipitate, if any, flocks together, and filter off any
precipitated copper sulphide, carbon, and silica. Boil
thoroughly for ten minutes and add 25 c.c. of sodium
phosphate solution (10 per cent.), followed by ammonia
until a precipitate just forms and is not re-dissolved.
Clear the solution by adding 2 c.c. of hydrochloric acid,
add a considerable amount of acetic acid, dilute to about
400 c.c., and boil. When the solution has boiled remove
it from the plate and add about a tablespoonful of



sodium thiosulphate. Boil again thoroughly for about
ten minutes, allow the precipitate to settle, and filter.
Wash the precipitate thoroughly with hot water and
ignite. If white it may be weighed at once as A1P0 4 ;
if not white it may be redissolved in a little strong
hydrochloric acid, the iron precipitated by boiling with
a fair excess of caustic soda, and the aluminium re-
precipitated in the filtrate exactly as before after adding
10 c.c. of sodium phosphate. Al in A1P0 4 = 22-10 %.

Chromium. Chromium if present will follow the
aluminium through all the steps of the preceding
estimation. It may be separated by fusing the pre-
cipitate in a platinum dish with sodium carbonate
containing a very little sodium peroxide. On dissolving
the melt in hot water, acidifying with sulphuric acid,
adding a little more sodium phosphate, and then making

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Online LibraryJ. A. (Joseph Allen) PickardModern steel analysis; a selection of practical methods for the chemical analysis of steel → online text (page 1 of 7)