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148.] SULPHUR. 561

from the well at the same time, and titrated with iodine, gave
0*007025 II 2 S per 1000. Instead of arsenous acid the precipi*
tation may be effected by means of cupric acetate together with
a little acetic acid, or by means of a silver solution, and the sul-
phur determined in the precipitated copper sulphide as barium
sulphate, according to 148, II, or the silver may be determined
in the silver sulphide in the metallic state. When copper salts are
used in very dilute solutions, the results are also too low ; whether
this is also the case with the silver solution I cannot say, from
lack of personal experience. The silver solution best adapted for
the purposes is recommended by LYTE * to be prepared by dissolv-
ing silver chloride in sodium-thiosulphate solution and adding a few
drops of ammonia. In an analysis of water containing iron sul-
phate, LYTE f threw down the hydrogen sulphide with freshly pre-
cipitated lead sulphate, filtered, washed, and extracted the lead sul-
phate with hot ammonium- acetate solution, converted the residual
lead sulphide into lead sulphate by oxidation with nitric acid, etc.,
and then weighed the sulphate.

In the case of mineral waters the method a is always to be
preferred, unless thiosulphates should be present anxi impair its
accuracy.

d. If the hydrogen sulphide is evolved in the gaseous state, an.d
large quantities are to be determined, the best way is to conduct it
first through several bulbed U-tubes (Fig. 103), containing an
alkaline solution of sodium arsenite, then through a tube connected
with the exit of the last U-tube, which contains pieces of glass
moistened with solution of soda, to mix the fluids afterwards, and
proceed as in ~b. If, on the other hand, we have to determine
small quantities of hydrogen sulphide contained in a large amount
of air, etc., it is well to pass the gaseous mixture in separate small
bubbles through a very dilute solution of iodine in potassium,
iodide of known volume and strength, which is contained in a long
glass tube fixed in an inclined position and protected from sun-
light. The free iodine remaining is finally estimated by means
of a solution of sodium thiosulphate ( 146); the difference gives
us the quantity of iodine which has been converted by hydrogen
sulphide into hydriotiic acid, and consequently corresponds to the

* Compt. rend., XLIII, 765. f Zeitschr. f. analyt. Chem., v, 441.



562 DETERMINATION. [ 148.

amount of the hydrogen sulphide present. The volume of the
gaseous mixture may be known by measuring the water which
has escaped from the aspirator used. The arrangement of the
absorption tube is the same as is figured in connection with the
Determination of Carbonic Acid in Air. The thin glass tube
conducting the gas into the absorption tube, however, must not
be provided with an india-rubber elongation.

From my own experiments* it appears that hydrogen sul-
phide, whether in small or large quantities, may be also estimated
by the increase in weight of absorption tubes. We have only to
take care that the mixture of gases is first thoroughly dried by
passing over calcium chloride. To take up the hydrogen sulphide
we use LT-tubes, five-sixths filled with copper sulphate on pumice,
one-sixth at the exit containing calcium chloride. To prepare the
pumice with copper sulphate, proceed as follows: Treat 60 grm.
pumice in lumps the size of peas in a small porcelain dish with a
iiot concentrated solution of 30 or 35 grm. copper sulphate, dry
the whole with constant stirring, place the dish in an air or oil
biith of the temperature of 150 to 160, and allow to remain
therein four hours. A tube containing 14 grm. of this prepared
pumice will absorb about 0*2 grm. hydrogen sulphide. It is well
always to employ two such tubes. If the prepared pumice is
dried at a lower temperature it takes up much less of the gas, if
dried at a higher temperature the gas is decomposed and sulphur-
ous acid is formed. This method is more completely detailed
under the Analysis of Black Ash.

Finally, small quantities of hydrogen sulphide mixed with other
gases may be estimated by passing through bromine water and con-
verting into sulphuric acid.

II. Separation and Determination of Sulphur in Sulphides.

A. METHODS BASED ON THE CONVERSION OF THE SULPHUR INTO

SULPHURIC ACID.

1. Methods in the Dry Way.

a. Oxidation ly Alkali Nitrates (applicable to all compounds
of sulphur). If the sulphides do not lose any sulphur on hu.tinu'.
mix the pulverized and weighed substance with 6 parts of anhy-

* Zeittchr.f. analyt. Chem., x, 75



148.] SULPIIUK. 563

drous sodium carbonate and 4 of potassium nitrate, with the aid
of a rounded glass rod, wipe the particles of the mixture which
adhere to the rod carefully off against some sodium carbonate, and
add this to the mixture. Heat in a platinum or porcelain crucible
(which, however, is somewhat affected by the process), at a grad-
ually increased temperature to fusion ;* keep the mass in that state
for some time, then allow it to cool, heat the residue with water,
filter the fluid, boil the residue with a solution of pure sodium car-
bonate, filter, wash, remove all nitric acid from the filtrate by
repeated evaporation with pure hydrochloric acid, and determine
the sulphuric acid as directed in 132. The metal, metallic oxide,
or carbonate, which remains undissolved, is determined, according
to circumstances, either by direct weighing or in some other suit-
able way. In the presence of lead, before filtering, pass carbonic
acid through the solution of the fused mass, to precipitate the
small quantity of that metal which has passed into the alkaline
solution.

Should the sulphides, on the contrary, lose sulphur on heat-
ing, the finely powdered compound is mixed with 4 parts sodium
carbonate, 8 parts nitre, and 24 parts pure and perfectly dry
sodium chloride, and the process otherwise conducted as already
given.

5. Oxidation by Potassium Chlorate. The oxidation of
metallic sulphides by a mixture of potassium chlorate and sodium
carbonate has been repeatedly recommended. It is advantageous
in so far that the sulphuric acid in the melt may be more readily
converted into barium sulphate than when nitrates are present;
on the other hand, it is dangerous because, when the mixture is
used in the proportions usually recommended 1 part sulphide,
3 parts potassium chlorate, and 3 parts sodium carbonate (or 4
parts sodium-potassium carbonate)- many sulphides, e.g., falil-
erz, antimony sulphide, etc., afford violent explosions. f Also
with many sulphides, like iron pyrites and copper pyrites (Fu.
MOI-IR), the decomposition is not complete. Great caution must
hence be exercised in using potassium chlorate in this method.

* If gas not free from sulphur is used for heating, some sulphur is likely to
be absorbed (PRICE, Journ. Chem. Soc. (2), u, 51). If a platinum crucible is
used, do not raise the heat more than is necessary or the crucible will be
attacked.

f Annal. d. Chem. u. l*liarm, t evil, 128.



564



DETERMINATION.



[ 148.



II. HOSE recommends taking 6 to 8 parts of sodium carbonate and
1 part of potassium chlorate to 1 part of substance.

b. Oxidation by Chlorine Gas (after BERZELIUS and II. HOSE,
especially suitable for sulpliosalts of complicated composition).

The following apparatus (Fig. 105), or one of similar con-
struction, is used. Corks should be used, not india-rubber stop-




Fig. 105.

pers, and wherever there is an india-rubber connection the glass
tubes should be close to each other.

A is a chlorine-evolution flask, * B contains concentrated sul-
phuric acid, and C calcium chloride. The sulphide to be decom-
posed is placed in the bulb-tube D, the straight tube of which
should be rather narrow and somewhat inclined, to prevent the
heavy fumes of the chlorine compound from returning, .ZTis the
receiver containing water (or, if antimony is present, a solution of
tartaric acid in diluted hydrochloric acid), F is a U-tube contain-
ing water, and G conducts the escaping chlorine into a carboy
containing moist calcium hydroxide.

AVhon the apparatus is arranged weigh off the substance in a
narrow glass tube sealed at one end, and carefully transfer



* 18 partsof salt mixed with 15 parts finely powdered manganese dioxide are
treated with a perfectly cold mixture of 45 parts sulphuric acid and 21 partsof
water. On shaking, chlorine is evolved, and when the evolution slackens, it
may be promoted by a gentle heat.




148.] SULPHUR. 565

from this to the bulb D in the mariner shown in Fig. 106, so that
no part of the substance is allowed to get
into the ends of the bulb-tube. When
the apparatus is filled with chlorine, con-
nect D and (7, and allow the chlorine to
act on the sulphide, and at first without

applying heat. When no further change is observed, and the
receiver E is completely filled with chlorine, heat the bulb D
gently, and take care to keep the tube warm also, in order to
prevent it from being closed up by the sublimate from a volatile
chloride. The sulphide is completely decomposed by the chlo-
rine, the metals being converted into chlorides, part of which
remain in the bulb and part (the volatile ones, like antimony,
arsenic, and mercury chlorides) distil over into the receiver. The
sulphur unites with the chlorine to form sulphur chloride, which
flows into the receiver E, where, coming into contact with water,
it decomposes, hydrochloric and thiosulphuric acids being formed
and sulphur precipitating. The thiosulphuric acid in turn decom-
poses into sulphur and sulphurous acid, and this last is converted
by the action of the chlorine in J? into sulphuric acid. The final
result of the decomposition is hence sulphuric acid, with more or
less precipitated sulphur. As the separation of sulphur renders
troublesome the further treatment of the contents of the receiver,
the separation is usually prevented by slowly heating, so that only
small portions of sulphur chloride reach the fluid (saturated with
chlorine) in E. The operation is concluded when no more products
(excepting perhaps a little ferric chloride, the complete expulsion
of which need not be waited for) distil over from the bulb. Then
heat the bulb- tube from D to in a manner to drive all the
sulphur chloride and volatile metallic chlorides into E, or at least
to the end of the bulb-tube.

Let the apparatus stand undisturbed for a short time longer,
then cut off the tube under the bend 0, and close the separated
end, containing usually a part of the volatile chlorine compounds,
with a smooth cork, or by inverting over it a glass tube sealed at
one end and moistened within. Let the whole now stand for 24-
hours to allow the volatile metallic chlorides to absorb moisture
and thus become soluble in water without generating heat. The
chlorides in the cut-off end are dissolved in diluted hydrochloric



566 DETEKMIN ATION. [ 148.

acid, the tube-end rinsed out, and the solution added to the con-
tents of the tubes E and F\ a very gentle heat is applied until the
free chlorine is expelled, and the fluid is then allowed to stand until
the sulphur, if any is present, has solidified. The sulphur is filtered
off on a weighed filter, washed, dried, and weighed. The filtrate is
precipitated with barium chloride ( 132), by which operation the
amount of that portion of the sulphur is determined which has been
converted into sulphuric acid. The fluid filtered from the barium
sulphate contains, besides the excess of barium chloride added, also
the volatile metallic chlorides, which latter are finally determined
in it by the proper methods, which will be found in Section Y.

The chloride remaining in the bulb-tube is either at once
weighed as such (silver chloride, lead chloride), or where this is
impracticable as in the case of copper, for instance, which remains
partly as cuprous, partly as cupric chloride it is dissolved in water,
hydrochloric acid, nitrohydrochloric acid, or some other suitable
solvent, and the metal or metals in the solution are determined by
the methods already described, or which will be found in Section
V. To be enabled to ascertain the weight of the bulb-tube con-
taining silver chloride, it is advisable to reduce the chloride by
hydrogen gas, and then dissolve the metal in nitric acid.

In cases where you have only to estimate the sulphur, say in
substances containing also sulphuric acid, O. LINDT* recommends
conducting the chloride of sulphur and the volatile metallic
chlorides into pure solution of soda, w r hen decomposition immedi-
ately takes place, producing sodium sulphide, sodium thiosulphate,
sodium chloride, and hypochlorite. When the decomposition is
over, continue passing the chlorine for two hours through the soda,
evaporate then to dryness, ignite the residue cautiously to destroy
the sodium chlorate, dissolve in water, and estimate the sulphuric
acid according to 132.

c. Oxidation by Oxide of Mercury (after BCNSEN).

This method, which will be found in detail, 188, is particu-
larly suited to the estimation of sulphur in volatile compounds, or
in substances which when heated lose sulphur.

* Zit8c7ir.f. analyt. Chem., iv, 870



148.] SULPHUK. 567

2. Methods in the Wet Way.

a. Oxidation of the Sulphur l>y Acids yielding Oxygen, or ly
Halogens.*

a. Weigh the finely pulverized sulphide in a small glass tube
sealed at one end, and drop the tube into a tolerably capacious
strong bottle with glass stopper, which contains red fuming nitric
acid (perfectly free from sulphuric acid f) in more than sufficient
quantity to effect the decomposition of the sulphide. Immediately
after having dropped in the tube, close the bottle. "When the action,
which is very impetuous at first, has somewhat abated, shake the
bottle a little ; as soon as this operation ceases to cause renewed
action, and the fumes in the flask have condensed, take out the
stopper, rinse this with a little nitric acid into the bottle, and then
heat the latter gently.

aa. The whole of the Sulphur has ~been oxidized, the Fluid is
perfectly clear : \ Evaporate with some sodium chloride, towards
the end adding pure hydrochloric acid repeatedly, cooling the dish
each time before adding the acid. Dilute with much water, and
determine the sulphuric acijd as directed 132. Make sure that the
precipitate is pure ; if it is not, purify it according to 132. Separate
the bases in the filtrate from the excess of the barium salt by the
methods given in Section V.

1)1). Undissolved Sidphur floats in the Fluid : Add potassium
chlorate in small portions, or strong hydrochloric acid, and digest
some time on a water-bath. This process will often succeed in dis-
solving the whole of the sulphur. Should this not be the case, and
the undissolved sulphur appear of a pure yellow color, dilute with
water, collect on a weighed filter, wash carefully, dry, and weigh.
After weighing, ignite the whole, or a portion of it, to ascertain
whether it is perfectly pure. If a fixed residue remains (consisting

* In presence of lead, barium, strontium, calcium, tin, and antimony, method
6 is preferable to a.

\ To test for sulphuric acid in nitric or hydrochloric acid, it is necessary to
evaporate on a water-bath nearly to dryness and take up with water before add-
ing barium chloride. When the acid cannot be got pure, determine the sul-
phuric acid and allow for it.

\ This can of course be the case only in absence of metals forming insoluble
salts with sulphuric acid. If such metals are present, proceed as in bb, as it is
in that case less easy to judge whether complete oxidation of the sulphur has
been attained.



068 DETERMINATION". [ 148.

commonly of quartz, gangue, &c., but possibly also of lead sul-
phate, barium sulphate, &c.), deduct its weight from that of the
impure sulphur. In the filtered fluid determine the sulphuric acid
as in aa, calculate the sulphur in it, and add the amount to that of
the undissolved sulphur. If the residue left upon the ignition of
the undissolved sulphur contains an insoluble sulphate, decompose
this as directed in 132, and add the sulphur found in it to the
principal amount.

In the presence of bismuth, the addition of potassium chlorate
or of hydrochloric acid, is not advisable, as chlorine interferes with
the determination of bismuth.

/?. Mix the finely pulverized metallic sulphide in a dry flask,
by shaking, with powdered potassium chlorate (free from sulphuric
acid), and add moderately concentrated hydrochloric acid in small
portions. Cover the flask with a watch-glass, or with an inverted
s.nall flask. After digestion in the cold for some time, heat gently,
finally on the water-bath, until the fluid smells no longer of chlo-
rine. Proceed now as directed in a', aa, or JJ, according as the
sulphur is completely dissolved or not. In the latter case you must
of course immediately dilute and filter. The oxidation of the sul-
phur may be usually effected more quickly and completely by
warming with nitric acid of 1'36 sp. gr. on a water-bath, and add-
ing potassium chlorate in small portions. Compare STOKER,* PEAR-
SON, and BowDiTCH.f

y. Aqua.regia is also frequently used. J. LEFORT^: recommends
a mixture of 1 part strong hydrochloric acid and 3 parts strongest
nitric acid. Complete conversion of sulphur into sulphuric acid,
however, is rarely effected by aqua regin.

6. Bromine may also be used. Pyrites or blende is digested at
a gentle heat with water, and bromine gradually added. If the sul-
phides have been prepared in the wet way, good bromine water is
sufficient to oxidize them. P. WAAGE prefers bromine to all other
wet agents, and advises its purification by distillation in an appa-
ratus from which ;ill caoutchouc connections are excluded.

b. Oxidation of tJw 8u,lj>/mr t>;/ < '/</<>/'/' < in Alkaline Solid'on,
t/f< r KIVUT. 1 i-:ri>ANT, and I)A(;uiN.|| (Suitable also for determining
the sulphur in the crude article.)

*Z:itftcJ<r.f. anali/t. Chem., ix, 71. f ^-. ix, 8'3. { Ib., ix, 81.

Ib , x, 20(5.

I Compt. rand., 1835,865; Jaurn. f. prakt. C?mn., i.xi, 134,



148.] SULPHUR. 569

Heat the very finely pulverized sulphide or crude sulphur for
several hours with solution of potassa free from sulphuric acid
(which dissolves free sulphur, as well as the sulphides of arsenic
and antimony), and then conduct chlorine into the fluid. This
speedily oxidizes the sulphur; the sulphuric acid formed combines
with the potassa to sulphate, which dissolves in the fluid, whilst
the metals converted into oxides remain undissolved. Filter, acid-
ify the alkaline filtrate, and precipitate the sulphuric acid by barium
chloride ( 132). Arsenic and antimony pass into the alkaline
solution in the form of acids, but not so lead, w T hich is converted
into binoxide, and remains completely undissolved. This method
is, therefore, particularly suitable in presence of lead sulphide. In
presence of iron sulphide, potassium sulphate is formed at first,
and ferric hydroxide, which, if the action of the chlorine is allowed
to continue, begins to be converted into potassium ferrate. As
soon, therefore, as the fluid commences to acquire a red tint the
transmission of chlorine must be discontinued, and the fluid gently
heated for a few moments with powdered quartz, to decompose the
ferric acid.

It occasionally happens, more particularly in presence of sand,
iron pyrites, cupric oxide, &c., that the process is attended with
impetuous disengagement of oxygen, which almost completely pre-
vents the oxidizing action of the chlorine. However, this acci-
dent may be guarded against by reducing the substance to the
very finest powder.

c. Regarding the method of CLOEZ and GUIGNET (oxidation
by potassium permanganate), see the Analysis of Gunpowder in
the Special Part.

B. METHODS BASED ON THE CONVERSION OF THE SULPHUR INTO
HYDROGEN SULPHIDE, OR A METALLIC SULPHIDE.

a. The determination of the sulphur in the sulphides of the
metals of the alkalies and alkaline earths soluble in water is best
effected provided they are free from excess of sulphur by I.,
J, or c. In the absence of acids of sulphur you may also convert
the sulphur into sulphuric acid by bromine water. The bases are
conveniently estimated in a separate portion, which is decomposed
by evaporation with hydrochloric or sulphuric acid, or when
none but alkali metals are present by ignition with 5 parts of
ammonium chloride in a porcelain crucible. If the compounds



570 DETERMINATION. [ 148,

contain excess of sulphur, they should be oxidized either by chlo-
rine in alkaline solution, or treated according to B, c, or C. If
they contain thiosulphate or sulphite, proceed according to 168.

b. The sulphur contained in alkaline fluids as monosulphide or
hydrosulphate of the sulphide may also be determined directly by
volumetric analysis, by means of a standard ammoniacal silver or
copper solution. In using the former, mix the solution with
ammonia, heat, and add the standard fluid till, on filtering off a
small portion and adding silver solution, a mere opalescence is
produced (.LESTELLE*). In using the copper solution, mix the
fluid to be tested with ammonia, heat to 50 or 60, and add the
standard solution, frequently shaking and boiling till no further
precipitation of CuO. 5CuS is produced, and the solution begins to
be blue (YERSTRAET f) . To make a standard copper solution 1 c. c.
of which shall equal 0-01, Na,S, dissolve 9-763 pure copper in
40 grm. nitric acid, boil, add 180 to 200 c. c. ammonia and water
to 1 litre. These methods are well adapted for technical pur-
poses, for the estimation of sulphide in soda lyes, for instance. It
need hardly be added that precipitated silver, copper, or lead sul-
phide (if you have used a solution of oxide of lead in potassa) may
be estimated gravimetrically.

c. If all the sulphur can be expelled from the substance in the
form of sulphuretted hydrogen by heating with hydrochloric acid,
the sulphide may be heated in a small flask with the concentrated
acid to complete decomposition and expulsion of the hydrogen
sulphide, the latter being determined according to I. If th^
substance is a liquid, the hydrogen-sulphide apparatus shown on
page 494 may be used for the expulsion of the carbonic-acid gas.
In this case, however, the tube h is replaced by a small upright con-
denser (see Special Part under " Analysis of Black Ash"). In
the case of polysulphides, the sulphur separated in the evolution
flask is collected on a filter dried at 100, washed, dried first at
70, then for a short time at 100, and weighed.

C. METHOD BASED ON THE SEPARATION AND WEIGHING OF THE

SULPHUR.

M. MORTREUX J recommends the following process for esti-
mating sulphur in alkali polysulphides: Extract 10 grm. with

* Zeitechr.f. analyt. Chem., n, 94, \lb. t iv, 216. \ Ib., I, 390.



149.] NITRIC ACID. 571

'boiled water, make up the filtrate to 100 grin, (or c. c.) with the
washings of the residue, and transfer 10 grm. (or c. c.) represent-
ing the soluble constituents of 1 grm. substance to a burette
provided with a glass cock arid of 40 to 50 c. c. capacity ; the
lower point should be narrow and cut off obliquely. Now add,
shaking the stoppered burette occasionally, sufficient of a solution of
1 part of iodine dissolved in 5 parts of potassium iodide and 50 parts
water to just decolorize the solution, and until a portion of the
fluid ceases to brown paper saturated with iron sulphate and dried.
Now add 8 to 10 c. c. carbon disulphide, stopper, and shake,
keeping the finger on the stopper. Keep the burette inverted for
a while, then place upright, and allow almost all of the solution of
sulphur in the carbon disulphide to flow into a weighed dish; in-
troduce a fresh portion of carbon disulphide into the burette,
mix, allow to run out, and repeat the operation once more.
After evaporating the carbon disulphide weigh the residual
sulphur.

Third Group.

NITKIO ACID CHLOKIC ACID.

149.

1. NITRIC ACID.
I. Determination.

Free nitric acid in a solution containing no other acid is deter-
mined most simply in the volumetric way by neutralizing with a
dilute solution of soda or ammonia of known strength (comp. Spe-
cial Part, "Acidimetry "). The following method also effects
the same purpose : Mix the solution with baryta water until the
reaction is just alkaline, evaporate slowly in the air, nearly to dry-
ness, dilute the residue with water, filter the solution which has
ceased to be alkaline, wash the barium carbonate formed by the



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