Journal of the Institute of Petroleum, Vol. 30, Sulphur by the lamp method

(1)

SULPHUR BY THE LAMP METHOD

(U sing Fast-B urning Lamp;

I . P . — 1 0 7 /4 5 (T e n ta tiv e )

S C O P E — .

1. (a ) T h ese m ethod s are su itable for the determ ination o f the total sulphur con ten t o f petroleum products such as gases, liquefiable gases, light distillates, kerosines, and gas oils. G as oils require d ilu tion w ith a v o la tile com b u stib le solvent o f know n low -sulphur con ten t. T h e m ethod can also be applied to com b ustib le m aterials n ot o f petroleum origin, but com in g w ithin the volatility range covered by th e ab ove p etroleum products.

No t e 1.— The m ethod has the follow ing advantages:

(i) The lamp specified for use with liquid products enables samples to be burned more rapidly than that prescribed in I.P.— 62.

(ii) T he lamp facilitates the com bustion o f highly aromatic materials without sm oking. In exceptional cases a small am ount o f aromatic free diluent o f known low sulphur content may be required.

(iii) Provision is m ade for carrying out the com bustion in purified air.

Civ) Sulphur present as carbon disulphide can be estim ated satisfactorily.

( b) T h e test solu tion s from th e absorber can be exam ined by volum etric, gravim etric or turbidim etric m ethods according to need.

T h ese are designated A , B and C respectively.

(c) T he results obtained by the volum etric m ethod (A ) are slightly high, ow in g to form ation o f nitric acid during com b ustion . For petroleum p roducts, th e error is usually o f th e order o f 0 01 per cent, sulphur, but it varies w ith the nature o f the sam ple and the con d ition s o f burning. T he results obtained by the gravimetric m ethod (B) and the turbidim etric m ethod (C) are n ot affected by nitric acid form ation, and are thus m ore accurate. M ethod B is su itable for sulphur con ten ts dow n to 0 001 per cent., and M ethod C for sulphur con ten ts dow n to 0 0001 per cent. M ethod C has a norm al upper lim it o f 0-005 per cent, sulphur, but this can be con sid erably extended by burning sm all quantities o f sam ple or by w orking w ith aliq u ot p ortion s o f the test solu tions.

A P P A R A T U S

2. T he apparatus (Fig. 1) sh all con sist o f the follow in g:

(a) Burner f o r Gases, o f heat-resistant glass and o f the form and d im ensions sh ow n in F ig. 2.

(b) L am p f o r Liquids, o f heat-resistant glass and o f the form and d im ensions sh ow n in F ig. 3.

(c) Chimney, o f heat-resistant glass and o f the form and dim ensions show n in F ig. 4. T h e neck o f the chim ney is fitted w ith tw o inlets for secondary air, and w ith a water-jacketed ou tlet (see N o te 2).

Note 2.— T h e u p p e r ru b b e r sto p p e r (see Fig. 4), w hich should be a t least 15 m m . fro m the u p p e r b en d o f the chim ney, is fitted before th e w ater-jacket is

(2)

2 SULPHUR BY THE LAMP METHOD (l.P .—107/45)

ASSEMBLY.

(3)

SULPHUR BY THE LAMP METHOD (i.P .— 107/45) 3 added. The lower end o f the outlet tube is bent when the water-jacket is in position and the low er rubber stopper is then fitted.

Alternatively, sealed glass joints may be used instead o f rubber stoppers.

(d) A bsorber, o f chem ically resistant glass and o f the form and d im ensions sh ow n in Fig. 5, packed to a depth o f 120 m m . with ch em ically resistant glass beads o f 4 - 6 m m . diam eter, supported on a perforated p orcelain filter p late o f approxim ately 20 m m . diam eter.

T h e drainage tube at th e b ottom o f the absorber shall be closed by a screw clip on a short length o f rubber tubing.

(e) D rechsel B ottle, o f 125-200 m l. capacity, coupled to the absorber as show n in F ig. 5.

( / ) F lowm eter, to m easure th e air con su m p tion o f the apparatus.

The design is o p tion al, but th e capillary type show n in F ig. 1, using light o il, is suitable. A capillary diam eter o f approxim ately 1 m m.

and length 10 cm . is recom m ended. T h e calibration range should be 1-5 litres o f air per m inute w ith a scale w hich is m arked at intervals o f n ot less than 0-5 litre/m in ute, and w hich can be read accurately by interpolation to the nearest 0T litre/m inute. O nly a sm all error is introduced by m easuring the gases after com bustion instead o f before, and it is con ven ient to instal the flow m eter at the

i 1-4.5 mm.± 0.5 mm.

I l

I I

Approx. 50 mm.

80mm.± 10mm. ||;A

25mm.±5mm

P r i m a r y A i r

Sample In le t

*-2 5 mm.-*

±5mm. ' F ig . 2.

BURNER FOR GASES.

(4)

d ischarge end o f th e absorbing system (see F ig. 1). A b ottle con taining lum p calcium ch loride is inserted betw een th e D rechsel b ottle and flow m eter in order to rem ove excess m oisture from the gases entering the flow m eter.

4 SULPHUR BY THE LAMP METHOD (i.P.— 107/45)

—*1 - F l4—

Fig. 3.

LAMP FOR LIQUIDS.

A . . 69-71 mm. I . 7 mm. ext. diam.

B . . 4 6 -5 0 mm. J . 6 - 1 0 mm.

C . . 29-5-30-5 mm. K . 10-18 mm.

D . 38-42 mm. L . . 4-9-5-1 mm. int. diam.

E . . 28-3 2 mm. 6-7 mm. ext. diam.

F . . approx. 40 mm. . M . . 10-5 mm. ext. diam.

G . . 14—18 mm. N . . 3-9—4-1 mm. int. diam.

H . . 1-2 mm.

The central wick tube is rounded off to form the slight constriction at N after the edges have been “ trued.”

The two parts o f the wick tube must be in line and there must be no con

striction at the joint with the main body o f the lamp.

There must be no bulge at the joint X .

(g) E lectric B lank.— A n electric heater w hich may be corked in to a chim ney, in p lace o f a lam p burning sulphur-free m aterial for the blank test, is sh ow n in F ig. 6. T h e details o f design are op tion al, but shall be such that when th e current is adjusted to give a dissip a

tion o f approxim ately 110 w atts, the elem en ts w ill glow at a m edium red heat.

(5)

SULPHUR BY THE LAMP METHOD ( i.P .— 107/45) 5 T he recom m ended form con sists o f tw o elem ents o f ^ -in c h diam eter p orcelain sleeves w rapped w ith asbestos paper and w ound closely w ith N o . 34 S .W .G . nichrom e wire, suspended from a heat-resistant glass rod, by w ires passing through the porcelain sleeves. C on n ection s to the elem ents, w hich m ay be in series or in parallel, accord in g to th e voltage available, are brought in through heat-resistant glass tubes passing through a cork w hich fits th e chim ney. T hese tubes are plugged w ith asbestos and sealed w ith d e K h otin sk i cem ent.

Fig. 4.

CHIMNEY.

A . . 1 0 5 mm. G . . 140-160 mm.

B . . 3 0 mm. int. diam . H . 19-5-20-5 mm.

C . . 2 5 mm. I 18-22 mm.

D . . 33-37 mm. J 15-25 mm.

E . . 30-40 mm. K . . 5-15 mm.

F 200-220 mm. L . . 9 mm. ext. diam.

(It) Rubber Band, o f approxim ately 1£ inch diam eter and inch length to seal th e cork jo in t betw een the chim ney and the lam p.

(i) C otton W ickin g.— C lean unused cotton w icking, w eighing ab ou t 5 -6 m g. per cm ., o f the type and quality usually sold as

13s/14 ends, scoured, and bleached. ■

(J) A ir S u p p ly.— A supply o f air, free from serious contam ination w ith sulphurous im purities and under a steady pressure o f approxi

m ately 2 in ch es o f mercury.

A higher degree o f freedom from sulphurous im purities is required for M eth od C than for M eth od s A and B . For M eth od C the w'eight

(6)

6 SULPHUR BY THE LAMP METHOD ( i.P .—107/45)

o f sulphur found in the blank test, due to the air, m ust be less than 0-2 m g. and preferably less than 0-1 mg. S om e o f the sulphur found in the blank test originates from th e reagents and d istilled

1M1

Fig. 5.

ABSORBER SYSTEM.

A . . 300 mm. H

13 . 120 mm. I

C . . 20 mm. J

D . . 140 mm. K

E -. . 30 mm. L

F . 140 mm. M

G . . 25 mm.

25 m m . 35 m m . 25 m m . 9 m m . 30 m m.

25 m m .

water, and an allow an ce sh ould be m ade for this w hen assessin g the purity o f the air supply. For M eth od A , th e air su p p ly m ust also be free from acid fum es or m aterials w hich w ill form strong acids in the apparatus, e.g ., carbon tetrachloride fum es.

(7)

I f the air has been purified (N o te 3) by scrubbing with aqueous reagents, steps m ust be taken to rem ove excessive hum idity w hich m ight lead to difficulty in regulating the lam ps, ow in g to the con d en sa

tion o f drops o f w ater in the rubber tubing where it is constricted by

gmp.

I I I I

SULPHUR BY -THE LAMP METHOD (i.P .— 107/45) 7

Fig. 6.

ELECTRIC BLANK.

screw clips. T his m ay be achieved by passing the air through a c o il o f tubing im m ersed in ice, fo llo w ed by a sm all separating vessel.

Note 3.—The procedure to be adopted for air purification depends on the location o f the laboratory. In residential districts, simple scrubbing in a con

tinuous washer with constantly replaced tap-water provides an adequate degree o f purification. In industrial districts, it may be necessary to use 1 per cent, aqueous caustic soda or stronger reagents. Treatment with concentrated sul

phuric acid, follow ed by an alkali wash and passage over activated charcoal, has proved successful in difficult cases. Bottled oxygen blended with bottled nitrogen or carbon dioxide provides an atmosphere o f low, though not negligible, sulphur content. I f bottled gas is used, a low-pressure reservoir, such as tw o 15-litre aspirator bottles coupled to form a water displacement gas-holder, is usually required in addition to constant pressure discharge valves on the cylinders.

(8)

P R E P A R A T I O N A N D A S S E M B L Y O F A P P A R A T U S

3. (a) General. W ash the chim ney, absorber, D rech sel bottle, and con n ectin g tube w ith d istilled w ater. A ssem b le th e apparatus as sh ow n in Fig. 1, m aking the con n ectio n s betw een the chim ney, absorber, etc., w ith rubber tubing. C on n ect th e air m anifold to the lam ps and chim neys by m eans o f -&-inch bore rubber tubing, and con trol the prim ary and secondary air independently by m eans o f screw clip s. D ivid e th e secondary air con n ection by m eans o f a tee-p iece after th e screw clip, so that th e tw o diam etrically op p osite openings at the base o f th e ch im ney are con n ected to the tee-piece.

C on n ect the jack et on th e ou tlet tube from th e ch im ney to a su pp ly o f tap water.

N o t e 4 .— S afety Warning. When burning gas samples, surround the chimney with a safety shield to p rotect the operator in case the chimney bursts through the accidental ignition o f an explosive mixture.

(b) P reparation o f Burner f o r Gas Sam ples. T ie a num ber o f lengths o f new co tto n w ick in g (usually five) in the centre w ith an extra length o f w ick. Pull the bundle (A , Fig. 2) by m eans o f the extra length (B, Fig. 2) in to the burner. C om b th e strands o f w ick parallel before p ulling them in to the burner, and trim th e bundle square. T h e bundle o f w ick sh ould be sufficiently tight to resist the flow o f gas through the burner, in order to prevent the flame from fluctuating or being extinguished by variations o f pressure in the chim ney caused by th e bubbling in the absorber. C onn ect the burner w ith the source o f gas by m eans o f rubber tubing.

(c) Preparation o f L am p f o r L iqu id Sam ples. Prepare a bundle o f w ick by w in din g three turns o f w ick round a form er con sistin g o f a strip o f w ood or cardboard approxim ately 170 m m . long. R em ove the w ick from the form er w ith ou t unw inding it or cu ttin g through the loop s, and insert the resulting six lengths in to the reservoir o f the lam p through the filling tube. Pull the w ick up into the w ick tube by m eans o f a h ook ed w ire so that 30 or 40 m m . project from the top. C ut through th e lo o p s and com b the threads ou t parallel w ith any su itable instrum ent, e.g ., forceps. D raw th e w ick back in to th e w ick tube and trim o ff level w ith the top. Push any w ick extruding from the filling tube in to th e reservoir. In som e cases it m ay be necessary to use m ore or less than six lengths o f w icking.

I f w opentane or other very volatile m aterial is to be burned, pull or tap the w ick d ow n to w ithin 5 -1 0 m m . o f the division in the w ick tube, and plug the w ick tube ab ove this level w ith a b undle o f w ick ab ou t 10 m m. lon g, and con sistin g o f 10 or 12 lengths o f w ick sim ilar to that in the burner for gas sam ples. G enerally, it sh ould not be pushed d ow n so far as to touch the m ain w ick.

L IG H T IN G A N D C O N T R O L O F T H E B U R N E R S A N D L A M P S 4. (a) Insert the burners or lam ps for a batch o f tests together w ith th e lam p or electric heater b ein g used for the blank test in to the

(9)

chim neys an d turn th e secon dary air on to give a volu m e o f ap proxim ately 2 litres/m in ute per lam p. (N o te 5.) D o n o t turn on th e prim ary air. R em o v e each burner or lam p in turn from the chim ney, ligh t and replace it. I f several are rem oved at the sam e tim e there m ay b e an excessive drop in pressure in the air m anifold.

(b) In th e case o f the burner, turn on th e gas and ign ite it. Turn on th e prim ary air and, after m aking any necessary adjustm ents to the gas and prim ary air, re-insert the burner in to the chim ney w hile tem porarily restricting th e secondary air. R eadjust the flame if necessary 'by regulating the gas and air supplies.

(c) In the case o f th e lam p, turn on the prim ary air and light the lam p, low erin g the w ick i f necessary by tapping th e lam p. R eplace th e lam p in th e chim ney w h ile tem porarily restricting the secondary air. R o ll th e rubber band d ow n over the cork join t. M ak e any necessary further adjustm ent to the flam e w h ile the lam p is in the ch im ney by tapping th e lam p to low er the w ick and by regulating the prim ary and secondary air supplies.

(d ) W hen all the burners or lam ps have been lighted, adjust the to ta l quantity o f air su pp lied to each burner or lam p, including the blank, so that each 'receives th e sam e am oun t as that requiring the greatest quantity.

(e) A fter a lam p has burned for a few m inutes and th e initial surplus liquid in the w ick con su m ed, it m ay be necessary to raise th e w ick a little w ith forceps to restore the flame to its original size. T h e w ick in th e gas burner sh ould not need adjustm ent p ro

vided that it has been correctly fitted.

( / ) Liquefied gas sam ples sh ould be drawn from b elow the liquid level in th e sam ple con tainer and allow ed to evaporate in the c o n  n ection s leadin g to th e burner. I f there is no b ottom con n ection , invert th e sam ple container. A rubber bulb, such as a sm all footb all bladder, con tained in a n et bag, slightly com pressed by a w eight, m ay be con n ected in to the sam ple lin e to the burner to ensure a steady pressure from such sam ple containers and also from gas sam ples w hich are being m easured w ith a bellow s-type meter.

(g) T o prevent b low -b ack o f gas sam ple into the air m anifold the prim ary air con n ection s to all gas burners m ust be m ade through a D rech sel b ottle con taining a little d istilled water.

Note 5.—The total air requirement per lamp varies with the type o f fuel and the rate o f burning. It is usually 2 0 -2 -5 litres/minute. T he quantity o f pri

mary air also varies with the type o f fuel and is o f the order OT-O-3 litres/minute, but is not measured separately. I f the correct quantities o f primary and second

ary air are used and the wick properly trimmed, the flame will be steady and will burn without sm oking. Poor trimming or excessive primary air will cause the flame to be irregular and pierced by a jet o f primary air. This latter con

dition must be avoided as it results in incom plete com bustion o f the sample.

Q U A N T I T Y A N D M E A S U R E M E N T O F S A M P L E

5. (a) Q uan tity. T h e am ou n t o f sam ple required depends on th e sulphur con ten t, but n orm ally use not less than the follow ing a m o u n ts:

SULPHUR BY THE LAMP METHOD ( i.P .—107/45) 9

(10)

10 SULPHUR BY THE LAMP METHOD ( i.P .— 107/45)

Product. Quantity.

. 7 g.

10 ml.

. 2 g.

G ases and liquefied gases Volatile liquids and kerosines . G as oils .

In th e case o f m aterials w ith a sulphur con ten t o f 0-005 per cent, or less, w hich are being tested by M ethod C, the ab ove quantities sh ou ld be d oubled.

{b) G ases an d L iquefied Gases. G ases and liquefied gases m ay be m easured by w eigh in g the sam ple container b efore and after burning the gas, or by th e u se o f a dry gas m eter in the case o f gas sam ples.

(c) V olatile L iqu ids an d K erosines. (N o te s 6 and 7.) V olatile liquids and k erosines m ay be m easured by volum e. A lternatively, the sam ple m ay be w eighed into the lam p, burned to dryness, and the last traces rem oved from th e w ick by burning 2 m l. o f a lc o h o l or sulphur-free petrolehm product.

No t e 6 .— Sam ples containing Tetraethyl Lead. For M ethods B and C , first free the sam ple from T.E.L. by vigorous agitation at room temperature with one-fifth o f its volum e o f 38-40 per cent, w t./w t. hydrochloric acid for 1 hour.

Separate the acid and wash the sam ple with distilled water till free from acid.

Ascertain whether removal o f T.E.L. is com plete by testing a small portion o f the acid-washed sam ple with bromine in carbon tetrachloride.

No t e 7 .— Sam ples containing Gummy M aterial. D eposition o f gum on the wick can be prevented or reduced by diluting the sam ple with rec.-butyl alcohol and, after burning to dryness, burning 2 ml. o f ¿ec.-butyl alcohol to clear the wick. Burn the sulphur in any char formed from gummy samples by raising the wick at the end o f the com bustion, using sufficient primary air to burn the top portion o f wick.

(d ) Gas O ils. (N o te 7.) W eigh the gas o il into the lam p, adding diluent first, to prevent flooding the w ick w ith neat gas oil. A lter

natively, pull the w ick clear o f th e b ottom o f th e lam p and tap it dow n after the gas o il and diluent are thorough ly m ixed. Burn to dryness, and then burn 2 m l. o f sulphur-free diluent to clear the w ick . I f th e diluent is not sulphur-free, an allow an ce m ust be m ade for the sulphur. T h e volu m e o f d ilu en t required is usually betw een 1 and 5 tim es the volu m e o f gas oil.

M E T H O D A (V O L U M E T R IC ) A P P A R A T U S

6. A s in S ection 2.

R E A G E N T S

7. f a ) H ydroch loric A c id Solution, con tain in g 2-275 g. o f HC1 per litre. T h e strength o f the solu tion is such that 1 m l. is equivalent to 1 m g. sulphur.

(b) Sodium C arbonate Solution, con tain in g 3-306 g. o f N a 2C 0 3 per litre. 10 m l. o f this solu tion sh ould exactly neutralize 10 m l.

o f th e h ydrochloric acid solu tion.

(11)

SULPHUR BY THE LAMP METHOD (i.P .— 107/45) 11 (c) Indicator, B .D .H . 4-5, or other indicator o f sim ilar p H range.

(d) E th yl Alcohol, absolute, o f sulphur con ten t less than 0-001 per cent.

(e) Diluent.— A lk ylate, petroleum spirit, w ooctane or other v o la  tile petroleum p roduct, o f low and known sulphur con ten t.

( / ) scc.-B u tyl Alcohol, o f negligible sulphur content.

(g) D istille d W ater, neutral to the indicator chosen.

P R O C E D U R E

8. (a) Prepare and assem ble the apparatus as in S ection 3, w ashing the chim ney, absorber, D rechsel b ottle, and con n ectin g tube w ith neutral d istilled w ater.

(6) P ip ette 20 m l. o f the sodium carbonate solu tion into the absorber and p lace approxim ately 30 m l. o f neutral distilled water in the D rech sel bottle.

(c) In th e case o f liquid sam ples charge the lam ps w ith the sam ple as in S ection 5.

(d ) Light th e burners or lam ps as in S ection 4.

(e) W hen burning is com p lete, turn o ff the air supply and rem ove the burner or lam p from the chim ney. R em ove the water con n ection s from the condenser, d iscon n ect the chim ney and condenser, and wash the in sid e w ith neutral d istilled w ater, collectin g the washings in a beaker. D rain th e solu tion from th e absorber into th e beaker by loosen in g the screw clip on the drain tube at the b ottom o f the ab  sorber. R em ove the adhering solu tion from the absorber by w ashing d ow n th e in let tu b e w ith a je t o f neutral distilled w ater and then directing a larger quantity round th e inside o f th e top o f the absorber, w h ile h old in g the rubber drain-tube between the fingers.

W hen th e w ashings cover th e beads, b low gently through the inlet tube, and then' co llec t the w ashings in the beaker by releasing the rubber drain tube. R epeat this operation twice. Then drain the con ten ts o f th e D rech sel b ottle in to the beaker and w ash the b ottle and tube w ith neutral d istilled water, collectin g the w ashings in the beaker.

( / ) A dd 6 drops o f in dicator solu tion to the contents o f th e beaker>

and titrate w ith the h ydrochloric acid. I f th e solution is acidic prior to titration, repeat th e determ ination, burning less sam ple.

(g ) In a sim ilar w ay, w ash ou t th e apparatus used in the blank test and titrate.

C A L C U L A T IO N A N D R E P O R T I N G

9. (a) C alculate th e sulphur con ten t by m eans o f the follow in g fo r m u la :

where A = volu m e in m l. o f HC1 required for the sam ple, B = volu m e in m l. o f HC1 required for the blank, and W = w eigh t in g. o f sam ple burned.

Sulphur, per cent. w t.

/

(12)

(6) R ep ort the result to th e nearest 0 01, as th e sulphur con ten t o f the sam ple, and in dicate that the determ ination w as m ade in accord ance w ith M eth od A , e .g . :—

Sulphur con ten t (I.P .— 107/45 (T) M eth od A ) = . . . per cen t. w t.

P R E C I S I O N

10. T est results sh ou ld n ot differ from the m ean by m ore than the fo llow in g am oun ts:

Product.

Sulphur, per cent, weight.

Repeatability (One operator and

apparatus).

Reproducibility (Different operators

and apparatus).

Gases, liquefied gases, volatile liquids and kerosines.

U p to 0-50 A b ove 0-50

0-01 per cent.

4 per cent, o f mean

0 02 per cent.

Gas oils U p to 1-50 A b ove 1-50

0-03 per cent.

0-06 per cent.

M E T H O D B (G R A V IM E T R IC ) A P P A R A T U S

11. A s in S ection 2.

. R E A G E N T S

12. (a) H ydroch loric A c id Solution, con sistin g o f concentrated h ydroch loric acid (approx. 36 per cent, w t./w t.) in an equal volu m e o f d istilled water.

(b) Sodium C arbonate Solution, con tain in g 100 g. o f anhydrous sodium carbon ate per litre in d istilled water.

(c) Indicator, B .D .H . 4-5 or other in dicator o f sim ilar p H range.

(d) Brom ine W ater, con sistin g o f a saturated so lu tio n o f brom ine in d istilled water. T he su lph ate con ten t o f the b rom ine m ust n ot be greater than 0-005 per cent, by w eight.

(e) E th y l A lcohol, ab solute, o f sulphur con ten t less than 0-0005 per cent, by w eight.

( / ) D iluent.— A lk ylate, petroleum spirit, w ooctane or other v o la  tile petroleum prod uct o f lo w and know n sulphur con ten t.

(g) se c.-B u ty l Alcohol, o f negligible sulphur con ten t.

13. (a) Prepare and a ssem b le th e apparatus as in S ection 3.

( b) P ip ette 20 m l. o f th e sod iu m carbon ate so lu tio n in to the absorber and p lace ap proxim ately 30 m l. o f d istilled w ater and 1 m l.

o f th e sod iu m carbon ate so lu tio n in th e D rech sel b ottle.

(13)

(c) In the case o f liquid sam ples con taining tetraethyl lead, rem ove th e lead as in N o te 6. Charge the lam ps as in S ection 5.

(d ) Light the burners or lam ps as in Section 4.

(e) Proceed as in S ection 8 (e), except that the distilled water need n o t be neutral.

( / ) C over the beaker w ith a w atch-glass and reduce the volu m e o f solu tion to 200 -3 0 0 m l. by b oilin g (N o te 8). F ilter th e solu tion w h ile h ot through a 12-5 cm . W hatm an N o . 40 filter paper in to a second beaker, and w ash any solu tion rem aining on the inside o f the first beaker and on th e stirring rod, i f used, in to the filter w ith hot d istilled water. W ash the filter tw ice by directing a je t o f distilled w ater round the ed ge o f the paper. A dd 10 m l. o f brom ine water to the con ten ts o f the secon d beaker, stir, and add 10 m l. o f h ydroch loric acid. C over th e beaker w ith a w atch-glass and heat to boiling. W hen th e brom ine has been expelled, add a few drops o f indicator. I f necessary, render the solu tion acid by addition o f h ydroch loric acid and exp el th e additional brom ine liberated.

A gain determ ine if th e solu tion is acid, repeating th e process i f it is not.

W hen the solu tion is acid, add slow ly to the b oilin g solu tion so that it d oes n o t cease b oilin g, 10 m l. o f barium chloride solu tion from a p ip ette inserted under th e w atch-glass. I f a high sulphur con ten t is anticipated, add on ly 1 -2 m l. o f barium chloride to “ seed ” the solu tion , and ad d th e balance o f th e barium chloride solution after the first precipitate is observed. T his w ill give a precipitate w hich is easily separable by filtration. B oil the solu tion for at least 30 m inutes after precip itation , and a llow to c o o l undisturbed for at least 6 hours.

H eat or b o il th e solu tion again, and filter w h ile h ot through an ash less filter paper, e.g ., 12-5 cm . W hatm an N o . 44, decanting the supernatant liq u or b efore transferring th e precipitate to th e filter w ith a je t o f hot d istilled w ater. I f p ossib le, w ash the precipitate tw ice by d ecantation before transferring to the filter. L oosen any p recipitate adhering to the beaker by m eans o f a rubber “ p o lice

m an ” and w ash into the filter w ith distilled water. W ash the filter eight tim es by directing a je t o f hot distilled water round the edge o f th e paper, a llow in g th e filter to drain com pletely after each w ash.

A fter th e final w ash, a llo w th e filter paper con taining the pre

cip itate to drain and then transfer it to a porcelain or platinum crucible for ign ition . A llo w the ignited precipitate to c o o l and w eigh to th e nearest 0-0001 g.

(g ) In a sim ilar w ay, wash out the apparatus used in the blank test and determ ine the sulphur.

Note 8.— I t is a n a d v an tag e to have a n a n ti-b u m p stirring ro d in th e beaker w hen th e so lu tio n is being boiled. A suitable ro d consists o f a plain glass ro d w ith a b o u t 1 cm . o f glass tu b in g sealed to th e low er end a n d annealed. W hen th e so lu tio n cools th e tu b in g fills w ith solu tio n w hich m ust be sh a k e n ,o u t before reh eatin g th e solution.

SULPHUR BY THE LAMP METHOD ( i.P .— 107/45) 13

(14)

14. (a) C alculate the sulphur con ten t by m eans o f the fo llow in g

fo r m u la : i

C 1 U f * (A - B ) x 13-73 Sulphur, per cent. w t. = pp--- where

A = w eigh t in g. o f barium sulphate ob tain ed from sam ple, B = w eigh t in g. o f barium su lph ate ob tain ed from blank, and W — w eigh t in g. o f sam ple burned.

( b) R ep ort th e resu lt to the nearest 0-001 as th e sulphur con ten t o f th e sam ple and in dicate that th e d eterm ination was m ade in accord an ce w ith M ethod B, e . g .:—

Sulphur con ten t (I.P .— 107/45 (T) M ethod B) = . . . p e r c e n t, wt.

15. T est results sh ou ld n ot differ from the m ean by m ore than the fo llo w in g a m o u n ts:

Product. Sulphur,

per cent.

apparatus).

R eproducibility (Different operators

and apparatus).

Gases, liquefied gases, volatile liquids and kerosines

0 001-0-100 A bove 0 1 0 0

0-001 per cent.

1 percent, o f mean

0-002 per cent.

Gas oils 0-001-0-300

A bove 0-300

0-003 per cent.

0-006 per cent.

M E T H O D C (T U R B ID IM E T R IC ) A P P A R A T U S

16. (a) A s in S ection 2.

(b) Turbidim eter, o f an y con ven ien t type.

(c) S tan dard D ipper, for m easuring a standard q uan tity o f approxim ately 0-3 g. o f the barium ch lorid e crystals.

(d ) N essler Jars, having a graduation corresp ond ing to the standard volu m e (N o te 9).

R E A G E N T S

17.. (a) 0-99—1 0 1 TV H ydroch loric A cid.

(b) 0-25/7 Sodium C arbonate Solution, con taining 13-25 g. o f anhydrous sod ium carbon ate m ade up to 1 litre w ith d istilled water.

(c) Bromine in Sodium H y d ro x id e Solution, con tain in g 10 g. o f brom ine and 10 g. o f sod ium hydroxide m ade up to 1 litre with d istilled w ater. T h e sulphate con ten t o f the brom ine m ust not be greater than 0-005 per cent, by w eight.

(15)

(d) Aqueous Sodium H yd ro x id e Solution, con taining 20 g. o f sodium h ydroxide in 100 m l.

(e) Phenolphthalein Indicator, con taining 0-2 g. o f p henolp hth alein in 60 m l. o f 90 p e r c e n t, ethyl a lc o h o l and m ade up to 100 m l. with d istilled w ater.

( / ) A lcohol-G lycerol Solution, con taining 3 3 -3 4 per cent, by vol.

o f glycerol o f A .R . quality, in eth yl a lcoh ol. T he alco h o l need not be anhydrous, but m ust be free from im purities, including traces o f hydrocarbon, w hich cause a p recipitate w hen the solu tion is mixed w ith th e test solution.

(g) Barium Chloride C rystals, BaCI2.2H 20 , passing a 20-m esh B.S. sieve and retained on a 30-m esh B.S. sieve.

(It) A c id Sodium Chloride Solution, con sistin g o f a 1-OAT-aqueous solu tion o f sodium ch loride con tain in g 200 m l. o f 1-OA-hydrochloric acid per litre.

(i) S tan dard Sodium Sulphate Solution, con taining 4-4375 ± 0-001 g. o f sodium sulphate m ade up to 1 litre w ith distilled water.

T his solu tion is used in preparing solu tion s con taining 0-02 mg.

per m l. o f sulphur for standardizing th e turbidim eter.

O') D istille d W ater, free from sulphate.

(k) E th y l Alcohol, ab solute, con taining less than 0-00005 per cent, w t. o f sulphur.

(/) D iluent.— A lk ylate, petroleum spirit, /.rooctane or other volatile p etroleum p roduct, o f lo w and know n sulphur content.

18. (a) C alibration o f Turbidim eter, (i) D ilu te a m ixture o f 15 m l. o f the standard acid sodium ch loride so lu tio n and an appro-, priate volu m e o f the standard sod ium sulphate solu tion with distilled w ater to the standard quantity (N o te 9) required for the turbidi

m eter.

(ii) A dd the- standard volu m e o f a lc o h o l-g ly c er o l solution, mix w ith the “ p o lice m a n ,” and, after allow in g the air bubbles to clear, determ ine th e in itial turbidity. A dd 0-3 g. o f barium chloride crystals, u sing the standard dipper, and m ix w ith the “ p olicem an ” until the crystals are dissolved. A fter th e lapse o f a standard tim e (N o te 9) rem ove any air bubbles adhering to the sides o f the cell and measure the final turbidity.

(iii) Vary the volu m e o f sod ium sulphate solu tion used to enable the entire w orking range o f th e instrum ent to b e covered.

(iv) M ak e a blank determ ination on the reagents used for calibra

tion and m ake the necessary allow an ce w hen drawing the calibration curve. S elect the scale so that the curve covers the range 0-0 to

1 -0 m g. and the sulphur con ten t can be read to th e nearest 0 001 m g.

Note 9.—The standard conditions vary with the make o f turbidimeter. In the case o f one instrument which is known to be satisfactory for this work the standard volum e chosen for the test solution prior to the addition o f the alcoh ol- glycerol is 100 ml. The volum e o f alcohol-glycerol used is 20 ml. and the standard time for precipitation is 10 minutes. An instrument should be chosen

SULPHUR BY THE LAMP METHOD (i.P .— 107/45) 15

(16)

16 SULPHUR BY THE LAMP METHOD ( l.P .— 107/45)

such that the scale subdivisions correspond to approxim ately 0 01 mg. sulphur, and so that 0-001 mg. sulphur can be obtained by interpolation.

(ib) Prepare an d assem ble th e apparatus as in S ection 3.

(c) P ip ette 20 m l. o f the sod iu m carbon ate so lu tion in to the absorber, retaining th e last few drops in th e p ip ette. A d d these to the D rech sel b ottle, to w hich a lso add approxim ately 30 m l. o f d istilled w ater.

(d ) In the case o f liquid sam ples con tain in g tetraethyl lead, rem ove the lead as in N o te 6. Charge th e lam ps as in S ection 5.

, (e) Light th e burners or lam ps as in S ection 4.

i f ) P roceed as in S ection 8 (e), excep t that the distilled w ater need n o t be neutral.

(g) P ip ette 10 m l. o f the 1 per cent, brom ine in sod ium hydroxide solu tion and fo llo w by 15 m l. o f th e 1 -ON hydroch loric acid (this m ay be added from a burette) in to the beaker con tain in g th e test solu tion . C over the beaker w ith a w atch-glass and b o il to expel brom ine and to reduce th e solu tion to less than the standard volu m e (N o te 9).

(/i) A llo w th e solu tion to co o l, add a few drops o f p henolphthalein and render alk alin e by ad d ition o f th e 20 per cent, sod ium hydroxide solu tion. N eu tralize w ith, and add 3 m l. excess of, 1 -ON h ydrochloric acid.

(i) F ilter th e so lu tio n co ld through a 12-5-cm. N o . 44 W hatm an filter paper in to a N essler jar. W ash any so lu tion rem aining o n the beaker and rod in to th e filter w ith d istilled water. A fter the filter has drained, w ash w ith d istilled w ater in to th e N essler jar, and m ake the volu m e up to a standard quantity (N o te 9). M ix the con ten ts o f th e N essler jar w ith th e stirring rod and transfer to the turbidim eter cell.

( k) A dd th e standard quantity (N o te 9) o f a lc o h o l-g ly c er o l solu tion by m eans o f a p ip ette and m ix w ith the “ p olicem an .” A llo w the air bubbles to clear and m easure the in itial turbidity. A d d 0-3 g.

o f barium ch loride crystals, using th e standard dipper, and m ix w ith th e “ p olicem an ” u n til th e crystals are dissolved. A fter th e lapse o f a standard tim e (N o te 9) m easure the final turbidity.

19. (a) D ed u ce th e w eigh t o f sulphur p recipitated as barium su lph ate from th e difference in turbidity bfcfore and after precipitation by reference to the calibration curve. I f the d eterm ination w as m ade on an aliq u ot p ortion o f the test so lu tio n , m ultip ly th e w eigh t o f sulphur fou n d in th e a liq u o t by th e appropriate factor.

( b) C alcu late th e sulphur con ten t by m eans o f th e fo llow in g fo r m u la :

Sulphur, per cent. w t. == x

w here A — w eigh t o f sulphur in m g. ob tain ed from the sam ple, B = w eight o f sulphur in mg. ob tain ed from th e blank, and W = w eigh t in g. o f sam ple burned.

(17)

SULPHUR BY THE LAMP METHOD (i.P .— 107/45) 17 (c) R ep ort th e result to the nearest 0 0001 as the sulphur con ten t o f th e sam ple, and indicate that the determ ination w as m ade in accordance w ith M eth od C, e .g . :—

Sulphur con ten t (I.P .— 107/45 (T) M ethod C) = . . . per cent. w t.

20. T est results sh ould n ot differ from the m ean by m ore than the fo llo w in g a m o u n ts:

»

Product. Sulphur,

per cent.

apparatus).'

Reproducibility (Different operators

and apparatus).

Gases, liquefied gases, volatile liquids and kerosines

0-0001-0-0050 A b ove 0-0050

0-0002 per cent.

0-0004 per cent.

G as oils 0-0001-0-0150

A b ove 0 0 1 5 0

0-0006 per cent.

0-0012 per cent.

(18)

Pr i n t e d i n Gr e a t Br i t a i n b y Ri c h a r d Cl a y a n d Co m p a n y, Lt d.,

Bu n g a y, Su f f o l k.