CEM U a ARNDT A OUCH LUI
Dea AS NATH NRA

 

THESIS FOR DEGREE OF M8.
ARNOLD AWOTIN

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A STUDY CF TIE ELECTROLYTIC ETHODS FOR
DETEAINILG LEaD IN BAsIVG PCYDERS.

thesis for Degree of kh. 5S.
arnold awotin

Lay, L9O1L7T.
The author wishes to acknowledge
the kindly suggestions of ur. D. T.
kwing whose Supervision has been of

great essistance in this investication.

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Table of Contents.

introduction and purpose.

Literature review.

juethods.

veparation of lead from retals electrolytically.

baking powders.

A Comparative study of some Jifferent wethods.
&@e wveposition of lead in nitric acid solution.
be Veposition of lead in hydrolyzed starch solution.
0. Leposition of lead in sucrose solution.
a. incineration of baking powder.
ee uodification of the Vorper Lethod.
f, luodifiecation of the i/ichnann uethod.

General discussion.

pummary °

9. wsLiterature cited.

 
introduction and Purpose.

baking powders have no food value in themselves but are
substances which by chemical reactions bring about, under cer-
tain conditions, the comparatively quick liberation of gas and
the consequent aeration of biscuit, bread, and cake. No sub-
stance that comes within tne domain of food inspection is the
subject of so much controversy as baking powder. Unless &
law forbids the use of a particular ingredient or class of in-
gredients, or in some manner regulates the labelling of the
package, no baking powder of any ..ind cén be considered adulter-
atec under the food law, unless it can be proved to be injurious
to health, or unless it conteins inert end useless mineral] metter.

the maximum emount of lead permissible in @ baking powder
is 2u parts per million, beceuse the lead salts are injurious to
health. she intention of the autnor is to find some accurate
electrolytic wetnod for aetcrisining lead in baxing powders.

This method ¢nould be oi coiisercisfl use.

Literature .tevicw.

Very little nes been cone in fle ueterninetion cf lead in
beking powders. The Bureau cr vunemistry, vashington, 3.C.,
Sterted this rroblen. in 1915. Lead wes ceteriined quantitative-
ly by gravimetric method in c:mparatively simple solutions and
the results were saticfectory. In 1916, the szeferee on Baking
Powders of Bureau of Chenistry continued the stucy of the aeter-

inination of leed in béexin;; powders. The Sauples consisted of

 
a synthetic baking powder nixed from ingredients in which the
lead contents had been previously cetermined. Kach s&auple
weighed 10C grems and consisted of 56 gm. mono=calcium phosphate,
25.5 grams of sodium bi-carponate, and 18.5 grams starch. The
lead content of the b&éx«ing sowder, caleulated trom the determina-
tions on the individauel inz,reaients as tude by wr. Seeker and
lir, Chittick, was 7 parts per million, or U.OCO? grams in each
1CO grem sanuple.

the methods used in the collaboration were the Axner and the

Wichmann rmethods. The following results were obtained by differ-

ent collaborators:

\ kxner i.ethod wWich:ann wethod
Collaborator
and (Analyst) wee of Lead : Parts per ug. of Lead : Parta per
per 100 g. : million per 100 g¢. : million
ne E. Stallings £20 20 1.4 14
Jel Sl Ue8 8
(J. O. Clarke ) , 0.6 6
U4 4
ved 3}
GC. B. hiorey 0.0 O 0.0 Q.0
(L. F. Hoyt) 0.0 QO 0.0 0.0
Tt. J. Bryan 12 le Ud 5
(J. Ke Davies) 164 14 1.0 10
re E. Doolittle 1.8 18 UA 4
(A. L. Burns) 140 Lv 1.2 12
Ke Re Lyman veO O 0.0 C
0.0 O

rom an examination of the above tuedle it will be seen that
the results very greatly, not only as a@ whole, but in duplicate
Samples determined by the same analyst. the results with the
Exner method run about twice as high as those with the Yichmann

method and about twice the actual lead content. The average of
the results with the “Wichmann method agrees fairly well with the
actual content of lead in the sa.ple but due to wide variations
in individual results the average cennot be considered of much
importance. The time consumed varies ¢reatly, that of Exner
method is from two to trree times that of Viechmann method.

the following table shows the inaccurate results which were
obtained in the ceterminetion of lead in bekinz powders by Seeker-

Cleyton, semington, and =xner methods:

Solutions contained 4CO mz. of lead per liter.

we thod leéad in milligrams rer liter of sciution
cOlution a D U
peeker-vla;ton 448 S20 384
74 192 194
xernington 410 L79 LUZ
597 58 140
Exner 157 121 513
281 £94

Solutions conteined £0 parts ot leed per million.

Method Polution «a DB U

seeker-Uleyton 35 16 19
£2 1 10

xemington 2k Y 5
£0 2 7

uxner 7 6 16
14 15

ihe remington modification uetnod shows a much closer egree-
ment of results than the reeker-Clayton. vith this method the
lerger weight of semple taken \1CO grams) reduces the error in

welgning. Still closer agreexent is found in the results with

 

the mxner method. {
ah wo

the ceposition of lead in baking powder by electrolysis
offers a means of shortening the determination. vr. bryan has
submitted a modification of the Corper method for electrolytic
deterrination of lead which he has found very satisfactory when
applied to phosphate beking powcers. at wes recorrmended that
this ethod be studied during 1916 and 1917.

A few experiments were nade by Lr. Patten on both clear
Solutions containing xnown quantities of lead, and upon solutions
of baking powders themselves. in clear synthetic solutions by
cepositing lead peroxide from nitric acid solution upon the anode
no deposit was obtained from lower quantities than 24 parts per
million, with 24 parts per million in solution, 60% of total lead
was deposited after 18 hours electrolysis with & U.ly(g,=1.8 A.
From dilute phosphoric acid solution, containing 50 parts per mil-
lion of lead, 95% of the total amount wes ceposited over night
with a GeDy UQzve’ tie

by adding dilute phosphoric acid to baking powder a pasty
mixture was obtained, trom woich with verying currents lead was
not deposited. Upon addition of a small emount of nitric acid
which partly hyarolyzed the starch, a deposit was obtained. wvhis
was so crusted over with starch and salts that it could not be
handled. When baking powder was completely neutralized with
nitrie acid and the starch hydrolyzed until a clear solution was
Obtained, no deposit was secured upon the anode with prolonged
electrolysis ena verying the current density.

further suggestions were meae by Dr. siske. ne states
thet the temperature of the solution during electrolysis should

not exceed 6U°G, and the time of electrolysis should exceed 7
hours, 14 to 15 hours used preferebly. 1o eliminate starch,
ur. tiske prefers the vatlin method, in which the beking powder
is ignited witn a strong solution of nefnesium nitrate and nitric

acid instead of the hydrolysis with hydrochloric acid.

wethods.

the gravimetric methods for uetermination of lead in baking
powders sre found in "Journal of association of vufficial agricul-
turel vhemists", seb. 1917. whe metnodas ere as tollows:
le veeker-vlevyton method.
26 remington wodification ot the seexer-vlayton wetunod,

oe mxner iuethod.

4. wiehmann wethod.

Neparetion of Leac from .wetals Llectrolytically.

~~ 6

she preciritation of lead es dioxide upon anode affords a
good rethod by which to separate it from otncr metals.

lhe electrolytic separation of lead is ecsily obtained from
the following retals: owperivm, strontium, valcium, uefnesiun,
the elxkeli metels, peryllium, vedmium, vhromium, ircn, Ureniun,
Zirconium, sinc, wickel, and Vobalt. in this case the solution
Should be made strongly acid, by sdding 20 ¢c.c.e of concentrated
nitric acid, Spe gre 1.35 = 1.58, to 100 c.c. of solution, with
anperage of 1.5 to 1.7, and voltae Of 2.5U - 2.5. Chlorides
must be absent.

veperation of Lead from vopper.= this separation is made

in the presence of free nitric acid.
peparation of Lead from mercury.- wy electrolyzing ae solu-
tion of these two metals in evujy nitric acid solution the separa-
tion mey be obtained.

weparation of Lead from sluminum.-= the seperation may be
made by uSing ecby nitric acid solution,becsuse aluninum is not
precipiteted electrolytically from a nitric acid solution.

weparation of Leed from arsenic.= the electrolytic separa-
tion of these two metals is not known.

peparation of Lead trom 4Antimony.- A purely electrolytic
separation is at present not known. this separation may be ob-
teined so: JUissolve beac and antimony in nitrie acid (4 e.c.),
water 15 c.c., lu grarns tartaric acid, add sulphuric seid (4 e.c.),
dilute to 25v c.c. un filtering from tre lead sulpnate, which
nee sepereted, the filtrete will contain ell the Antimony. ‘he
lead sulphete snovla be Cisested for 6 few minutes with ammonia

Ter. A.d to the lead hyuroxide nitric acid end electrolyze.

a
a9

separation of Lead from 1ine=- the gravimetric seperation
of the two tsetals is rrefereble.

wead méeéy be obtsinec as etal On céethoce by electrolyzing
Solutions of double oxalates, the acetate, the oxide in sodium
hyaroxiae, or the phosphate dissolved in the latter reagent or
in phosphoric acid of 1.7 Sp. gre while the retal separates
well trom either of those solutions, diitficulty is experienced
in drying the aeposit, tne most metel almost invariably suffers
& pertial oxidation, thus rendering the results high. it may
be dried in atmosphere of hydrogen, but this is e:pensive and
tedious.

rhosphoric ecid, mercury, arsenic, vhlorides, and Manganese

interfere with the deposition of leéd electrolytically, these
metals should be removed gravimetrically before electrolyzing

lesa solution.

viasses of baking srowder.

baking powders are divided naturally into three main
clecses, with reterence to the ec1da principle.
le sartrate powders, wherein the acid principle is bitartrate
of potassium or tertéeric acid, typified by the following reactions.
(a) KHC,HyO,g + MAHCO, = KiieC,H,O, + COp + HoO
(bd) HoC,H,O, + 2TBHCO, = ManC,H,0,-2H:0 + 2005

In tartrate powders available carbon dioxide is about 12.6%.
Ze Phosphosphete rowdcers, in which calcium acid phosphate is
the acid principle:

Cal, (PO, )o + 2TeHCO, = CaHPO, + HanHPO, + 2005 + 2H,0

This baking powder contains about 13% available carbon
dioxide.
3 Alum powders, wherein the acidity is due wholly or in part
to Sulphate of aluminum as it occurs in potash or ammonia alun,
or in the double sulphate of aluminum and sodium.

The reaction should be as follows:

Ky Alo (S0g)g + 6IBHCOg = 2AL(OH)z + SlagS0, + K_S0g + 6C0p

Available carbon dioxide is about 8%

Naturally many baking powders of complex composition are

met with, embodying various mixtures of the above classes.
Composition of Verious Baking Powders.

Followin; are analyses of typical bakin, powders of the

above classes:

Cream of Tartar Baking Powder:

 

Total carbon dioxide, COs 13 621
sodium oxide, th50 13.28
Potassium oxide, K,0 14.93
Calcium oxide, Cad 0.18
Tartarioc acid, C4H,0, 41.60
Sulphuric acid, SQ, 9.42
Starch 7.42
Water of combination and |
association by difference 8.98
100.00
Phosphate Baking Powder:
Total carbon dioxide, CO, 13 247
Sodium oxide, Mao0 12.66
Potassium oxide, H,0 0,31
Calcium oxide, Cad 10.27
Phosphoric acid, Pp0- 21.83
Starch 26.41
Water of combination and |
association by difference 15.05

 

100.00
=9 ww

Alum Baking Powder:

 

Total carbon dioxide, COs 9.45
Sodium oxide, Ta 20 2.52
Aluminum oxide, Al 20 3.73
Ammonia, Wz 1.07
Sulphuric acid, 50, 10.71
Starch 43.25
Water of combination ana |
association by difference 22627
100.00

Mixed Powders:

Total carbon dioxide, CO. 10.68

Sodium oxide, Ne o0 14,04
Calcium oxide, Cao 1.29
Aluminum oxide, Alp0z 4.59
Ammonia, Ws 1 £13
Phosphoric acid, Po05 3.38
Sulphuric acid, 50g 11.57
Starch 42,95

Water of combination and
association by difference 10.39

100.00
=] Ou

A Comparative Study of Some Different Methods,

The necessary apperatus is shown on next page and con-

sists of a storage battery, the potential of the current

at the battery is 664 volts. For measuring the current

a voltmeter and ammeter, graduated to 0.1 volts and 0.1

amperes respectively, is used. The resistence box is used

for varying the current. A deposition bath consists of

platinum dish which at the same time is anode, the cathode

consists of platinum electrode. The electrode is supported

in the proper position by ringsteand and clamps, The plat-
inum dish is sup.orted by ringstand so thet it may be heated

by a Bunsen burner. Connections are wace to the platinum

dish, electrode, resistance box, and ammeter, as shown in

the accompanying diefran. The temperature durin: elec-

trolysis wes 50=-60°C,.
+ é,
\-
o< @ “~~
oe ; .
e
@ :
WG t
°
A aA~
1. oOtorase battery of three cells, cepscity = «
and 6.4 volts.
<. Resistance box.
3. Platinum dish for anode.
4, Platinin electrode for cathode.
5. Ringestend with astestusp and copper tri+:.gle.
6. Bunsen burner,
7 Anmeter and voltmeter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E.

  

 

 

Wire connections.

 

 

el,

4.2,
=12=

Deposition of Lead in Mitrie Acid Solution.

Prepare a lead nitrate solution containing Ook gm. and

0» OL em. of lead per liter. Measure 50 c. Ce of each solution,

add 10 c.c. concentrated nitric acid sp. gr. 1. 54 and elec-
trolyze for three hours with CDs oo” le 6 and a voltage of about
42. The temperature of the bath should be from 50-60°C.

Upon completion of the electrolysis the solution is siphoned

out with constant acding of distilled water. The platinum

dish is washed and dried for two hours in oven at a temperature
from 200-210°C. The lead is weighed as lead peroxide and
multiplied by factor 0.8661 to obtain the weight of lead,

Results:

Wte of lead in solution Wt. of lead found

0.01 gm. 0.01 gm.
0,005 gm. 0. 008 em.

This experiment proves that all lead can be deposited as

PbO. during 3 hours at 50-60°C and with 1.5 amperes.

Deposition of Leaa in Hydrolyzed Starch Solutions.

A 10 gram sample of starch is weighed out, 20 c.c. of

concentrated nitric acid and 40 c.c. of water are added, the

Solution is heated until the starch is hydrolyzed; it is fil-

tered and lead nitrate solution added in different amount.

The solution is made up to 100 a.c. The experiment is run

for 3 hours with 1.5 amperes and 4. & volts at temperature from

50~60°C,. The lead is deposited as peroxide on anode.
~13-

The following results were obtained:
Grars of lead found.

Grems of lead added Parts per

to 10 gm. starch solution. million.
0.001 10 0.0
0-005 50 0.0
0.01 100 00
0.02 200 0.0
004 400 0.0
008 800 0.0

The experiment was further carried out by adding to 0.5 gm.

of hydrolyzed starch solution 0.008 gm., 0.004 em., 0.001 en.,
0.0005 em., and 0.0001 em. Of lead as lead nitrate, the solu-

tion was made up to 100 c.c. and electrolyzed as in the pre-

ceding experiment.

results:

Grams of starch Grams of lead Grars of lead found
in solution. added, after 3 hours,

0.5 0.008 0.0011

Od 0,004 0.0003

O05 0-001 0.OCC1

05 0.0005 0.0

0.5 0.-O0C01L 0.0

The above two tables show thet hydrolyzed starch inter-
feres with the deposition of lead as peroxide on anode; if
the amount of it in the solution is high, as in this case
10 gm. of starch in 100 c.c. of solution, no deposit of lead

peroxide is obtained, although the solution may have 1000

parts of lead per million. smaller amounts of hydrolyzed

starch retard the complete deposition, but some lead peroxide

can be obtained on the anode,
wl4—

Deposition of Lead in Sucrose Solution.

The experiment was repeated with sucrose solutions,
Five grans of sucrose are dissolved in distilled water, 0,001 ¢n.,

0.0025 gm., 0.02 gem., and 0.08 gm. of lead added as lead nitrate,
20 c.ce of concentrated nitric acid added, the solution is made

up to 100 c.c. and electrolyzed for 3 hours with 1,5 amperes and

4,2 volts. The temperature of the bath is 50-60°C. The wash-

ing, drying, and weighing of lead peroxide were done as in the

preceding experiments.
results:

Grams of gucrose Grams of lead Grams of Pb found.
in solution. added.

5 0.001 0.0

5 0.0025 0.0

5 0.020 0.0

5 0.080 0.0

The following data were obtained by electrolyzing lead

nitrate in 1% sucrose solution.
Grams of lead. Grams of lead

Grans of sucrose
in 100 c.c. Solution. found,
l gm. 0.0250 0.0091
1 * 0.0005 0v0
1 * 0.0010 0.0
1 * 0.0035 0,0

The avove two tables prove that sucrose, like invert

sugar (hydrolyzed starch), interferes with the deposition of
No deposit is obtained in 5% sucrose solution, although

leede
In 1% sucrose

the cuantity of lead is 800 parts per million.

solution a slight deposit is obtained when the content of lead

is 250 parts ver million.
~15—

Incineration of Bakin: Powder to Ashes,

Weigh out 100 grams of bakin: powder into a casserole,
add 50 o.c. concentrated nitrie acid and 20 c.ce concentreted
Sulphuric acid, heat in hood on small flame to avoid spattering;
heat until dry, place in a furnece at 600°C and heat to light
redneSSe The lead will be in tne form of svulphete. Leach
the ash in hot satureted ammonium acetate solution (several
leachings are necessary), filter, neutralize filtrete with am-
monia, and pass hydrogen sulphide until saturation, allow to
settle, filter and dissolve the rrecipitate in hot 20% nitric
ecid. Klectrolyze the solution in weighed platinum dish, using
platinum dish es anode and electrode és cathode. The tempera-
ture of beth is kept from 50-60°C. The current is run for 5
hours with ampcrage of 1.5.

after electrolysis, remove the liquid with a siphon tube
in the usual rianner. Dry and weigh.

vith this method no deposit was securec upon the anode.
The quantity of asn is large and bulky, and practically impos-
Sible to extract the lead sulphate with ammonium acetate. This
method seeus to give very low results, sometimes no deposit was

detected.

Modification of the Corper Method,

The depositing electrode, anode, is made of a piece of
platinum foil (2 inches in diameter) welded to a platinum wire
about 6 inches long, the cathode is made of platinum wire wound
into a spiral. The beaker used for electrolysis is a 400 c.c.

Jena beaker with lip.
~16-

In use the two electrodes are brought close together (the
anode above the spiral cathode 1 om. apart) and within 2 cm,
from the bottom of the beaker. Siphon tube is essential for
removing the liquid after electrolysis is complete and consists
of a bent glass tube. The apraratus iS arrérged as on diagram
on pege ll.

A100 ;-rem Sample ot baking powder is weighed out into a
400 c.c.e beaker and 55 c.c. of concentreted nitric acid carefully
eadea, the peaxer is heated in the weter pdeth until the starch
is hydrolyzed. The solution is diluted to 550 c.c. end elec-
trolyzed for 6 hours with ampereze of about 1.5 CD; o9 and volte
age 664. ‘he temperature oi the bath is xe pt from 50-60°C,
The platinum electrode, anoce, is removed, washed in distillea
weter, dried in oven at 200°C, and weij;hed cs lead peroxide.

Wo cevosit wes secured upon the anode with six hour elec-
trolysis. The experiment wes repeatec by adcing to the hydro-
lyzed baking powder solution different cuantities of lead

nitrate, but all the results were rnegetive.

Data:
Grams of tveking powder Grams of rb Grams of lead
in solution. added. found.
100 EUS e 0.001 UeO
" " 0.005 0.0
m " Ovl00 0.0
0.0

" " e200
luodification of the iichmann kiethod.

100 grams of beking powder are weighed out into a 1.2 liter
beaker and 80 c.c. Of hydrochloric acid (50 c.c. concen. + 30
water) added in small portions with constant stirring to avoid
frotning. whe mixture of acid and baking powder is heated until
the starch is hydrolyzed end the solution is quite limpid. After
cooling, 200 c.c. 50% ammonium citrate solution ere added, ‘The
soluticn is kept cola while @ Slight excess of ammonia is slowly
ena carefully added. if a precipitate forms, svificient ammonium
citrate is added to dissolve it. 15 c.ce Of LUo mercuric
chioride ere added and tne solution diluted to abont 1000 c.c,
The solution is saturatea with hydrogen sulphide end set aside.
The precipitate settles repialy end cen be readily filtered,
There is no need of standing, over nisht as the heavy mereuric
Sulphide will carry down the lead sulphide. If the solution
stands over night a precipitate of celeium citrate is apt to form,

The filter paper and sulphides ere placed in a small cas-
serolie. 1U ec.ce Of concentrated nitric acid end 2 a.c. of
concentrated sulphuric acid are added. The nitric acid is
evaporated and the sulphuric acid slowly fumed off. The
casserole is heated on a wire gauze to a light redness. The
mereury Salts will vaporize end any ferric sulphate present
will be broken up to the oxide. after cooling, add about
20 @.ce Of Saturated ammonium acetate solution, heet on water
bath ana filter by decantation, repeat this three times. ‘Yash
the filtrate with hot water. The filtrate is made neutral or

Slightly alkaline with ammonia and wermed, hydrogen sulphide
is passed till precipitation is complete, the precipitate is
allowec to settle End is then filtered.

Dissolve the precipitate in 20% nitric acid solution
(10 c.c. concen. HNO, + 5U c.ce weter ) ana hyérelyie for 4
hours with smperagse or 1.5 CDy 09 and 4.2 volts. ‘The tempera-
ture should be 50-60°C. | siphon out the Solution properly.

Dry in oven at 220°C for 2 hours, weigh as lead sverozide and

multiply the wei, nt by f.ctor vu.-8661 to obtain the weight of

leade
pata;
beking rowders Grams of Pb per Parts per
1C0 § [5 e of being Million.
powdere '
Lream of VTartrete v.0CO5S 5
Phosphate 0.0012 12
Alum 0.0010 LO
luixed povders 0.0009 9
0.0008 8

The eferee on Bekin; Powder sent six samples of baking
powder for collaborative work:
woe 1702, iionocalecium Phosphate Beking Powder.

No. 1712, Sodium Aluminum Sulphate Baking Fowder.

Wo. L722, Sodium aluminum Sulprate and lLionocalcium
: Fhosphate Bakin: Fowaer.

No. 1711, Sodium Aluminum Sulphate Baking Powder.

No. 1721, Combination Fhosppate and Sodium Aluminum
Baking Fowder.

No. 1701, WMonocalcium Phosphate Baking Powder,
~19={

The leaa was determined by ‘jichmann iJodified kethod and

the following results were obtained:

baking Powder. Gms. of Pb per 100 ge. Parts per
‘ Billion,

lon 1702 0.0048 48
060057 07
Loe L71E 0.0081 Sl
Us0080 80
oe L722 0.0084 84
: Ue0085 85
No. 1711 0.0 0
Woe 1721 0.0 8)
0.0 0

Oe L7OL 0.0 OQ

General Discussion,

The deposition of leed in bakins powder by electrolysis
makes the determination Shorter and more eccurate,. The pre-
GQipitation of lead as dioxide upon anode affords an excellent
method by weich to separate it trom the other netals. Only
three netals ere ceposited on the anode: lesd, manganese and
thallium; but strong nitric acid solution prevents the deposi-
tion of tne last two. starch and sugars interfere with the
aeposition of lead. The author's intention is to remove starch
gravimetrically ana deposit the leuu a&s peroxide upon the anode.
He selected Vichmann's iethod and modified it by reprecipitating
the lead acetate with hydrogen sulphide, dissolving PbS in 2Uo

nitric acid and electrolyzing the solution.
=o Uae

she deposition of lead as metal is not desirable, the

drying is impossible due to rapid oxidation of lead by oxygen,

tne results will be usually higher. Lead as metal does not

adhere firmly to the electrode. he deposit is spongy end

may easily be washe« away. where may be carried uvon the

cathode other metals if they are present.

the method is not very accurate. The complete removal

of arsenic, tin, and zine is not possible. the experiment

cannot be accomplished in one day. the method is not accurate

for commercial use.

Summary .

the gravimetric determination of leed in baking powders
is very unsatisfectory; the results vary greatly, not only as
&2 whole but in durlicete ceternminations.

the xemington modification method shows much closer check-
ing than the Seeker-VUlayton. The Exner method is very tedious
and long and gives great veriation in duplicate samples by the

Same analyst. The averese of the results with Vichmann method

egrees fairly well with actual content of lead in the Sample,
but due to wide variations in individual results the everage
cannot be considerec of much importance.
he Bryan modification of the Corper method hes been
found very satisfactory when applied to phosphate baking powders.
A few experiments were made by Dr. Patten upon determina-

tion of lead in bakin; powders electrolytically, but the results

were unsatisfactory.
Me deposition of lead as dioxide uvon anode affords a
good rethod by which to separate it from other metals.

The deposition of lead as metal is not desirable, the
results will be usually higher due to rapid oxidetion of lead
in drying.

Sterches and sugars interfere with the derosition of lead
upon tne anode and should be removed gravimetrically.
"Incineration of pexin, rowder" and

The two rethodas,

"odification ot tne VCorver wetnou", are undesirable. 40

lead was detected by these i.ethocs.
The autnor's modificetion of the ‘jichnann method gives

the results of cuplicete Sennles fairly setisfectory.

Literature Cited.

etcrminetion of Lead end zeferences to the Literature.
Edgar ¥. Smith, #lectro sanelysis, Sth ed. (1911) pe. 1C4.

Go

Separation of iwetals -— Lead.
Edgar if. coith, blectro dAnalysis, Sth ed. p. 233.

The Lead Voltsmeter.
Ae G. Betts « E. i. Korn: Trens. Am. Electrocher.

Soc., 6, 67 (1904).

tlectrolytic Precipitation of bead from acetate Solutions.
ie Ce. Snowdon: Ibid., 9, 223 (1906).

Electrolytic Deposition of Lead and Zine as affected by the

Addition of Certain Crganic vompounds.
S. A. Tucker « E. G. Thomsen: Ibid., 15, 477 (1909).

Effect of Addition Substances in lead Flating Baths.

F. C. Mathers « O. Xalph Uvernan: Ibid., 21, 513 (1912).

Electrodeposition of Lead.
F, C. Mathers: Ibid., 23, 153 (1913).

Solid, thick Deposits of Lead from Iead Acetate Solutions.
F. C. Mathers: Ibid., 24, 315 (1913).
Electrodeposition of lead from Lead Acetete Solutions.
fF. C. Mathers: Ibid., £5, 99 (1914).

Electrodeposition of Smooth Solid Lead from Lead litrate Solutions
F. C. Liathers « d4sa woKinney: Thid., 27, 131 (1915).

Some lew Features in the Electrolytic Determination of Lead,
Je Ge Fairchild: Jd. ind. Eng Chen, 3, 90.

Blectrolytic Determination of Lead in Large end smell Amounts
Using a Gauze Cylinder Electrode.
Be Woiciechowski : et. Chem. Eng, LO, 108.

Electrolytic Determination of Lead.
E. List: Ibid., 10, 1355.

Conditions for Lead Determination.
Alexander Classen: Quantitative Cherical Analysis by

itlectrolysis.

 
 

 
 

    

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