^rio. Dcpt.

Issued March 9, 1910.

United States Department of Agriculture,

BUREAU OF CHEMISTRY— Circular No. 53.

H. W. WILEY, Chief of Bureau.

SUGGESTED MODIFICATION OF THE WINTON LEAD NUMBER,
ESPECIALLY AS APPLIED TO MIXTURES OF MAPLE AND CANE
SUGAR SIRUPS.

By S. H. Ross,
Acting Chief, Omaha Food and Drug Inspection Laboratory.

APPLICATION OF THE ORIGINAL METHOD TO KNOWN MIXTURES.

The lead number as originally devised by A. L. Winton a was in-
tended to distinguish pure maple sirup from mixtures containing cane
sugar sirup. The practice of adopting a standard lead number for
pure maple sirups and then calculating the percentage present in a
given mixture or compound sirup from the lead number obtained
thereon is questionable. The value of the lead number for this pur-
pose can be readily determined by tests made on mixed sirups of
known composition.

At the suggestion of Doctor Winton, a preliminary test was made
by the writer in the Chicago laboratory. The lead number was
determined on two sirups: A, an alleged pure maple sirup, and B,
a mixture of 50 per cent by weight of A and 50 per cent by weight
of a cane sugar sirup of the same specific gravity. The lead number
on A was 0.90 and on B only 0.29, instead of the theoretical 0.45.
The apparent percentage of the maple sirup A in this mixed sample
was, therefore, approximately 32 per cent instead of 50 per cent,
which was actually present. The following study of this point was
made at the Chicago laboratory:

Sirups C and D, containing 65 per cent of solids, were made from
two supposedly pure samples of maple sugar. Another sirup, S,

a J. Amer. Chem. Soc., 1906, 28 : 1204.
24490— Cir. 53—10

was made to contain 65 per cent of cane sugar. Mixtures were made
of C one part, 8 one part; C one part, 8 three parts; D one part,
S one part ; D one part, S three parts, all by weight. The lead num-
bers were then determined on the sirups C and D and on the mixtures
in the usual manner, with the following results:

,—

Winton lead numbers on known mixtures (Hendrickson).

Sirup. ^

Lead number.

Maple sirup content.

Actual.

Calcu-
lated.

Appar-
ent.

Actual.

C..

1.20
.52
.08
1.22
.55
.19

Per cent.

Per cent.
100
50
25
100
50
25

C-S

0.60
.30

43.3
6.7

c-s...

D.

D-S. . .

.01
.31

45.1
15.6

D-S

ERROR INTRODUCED BY CARBON DIOXID IN DISTILLED WATER.

Winton a determines the standard of the lead subacetate solution
in 25 cc by the lead sulphate method in the same way as in the test
itself. On diluting 25 cc of the lead subacetate solution to 100 cc,
precipitation of the lead occurs which varies from an opalescence to
a decided turbidity, depending upon the quality of the distilled water.
The distilled water used in the following experiments was either freshly
boiled and the containing vessel connected with a soda lime tube
while cooling, or redistilled from caustic potash. The water pre-
pared by either method gave an opalescence or slight turbidity in
the blank test, which turbidity appeared within five minutes after
making the dilution but did not materially increase on standing in a
stoppered flask for three hours. This time was adopted as the mini-
mum, since one hour failed to give uniform results. To ascertain the
amount of lead precipitated in the blank or standard, determinations
were made upon 10 cc aliquots before and after filtering, with the
following results:

Weight of lead sulphate from 10 cc —

Unfiltered...

Filtered. .

Gram.

0. 1673
.1676
.1645
.1645

This difference is not so important on pure maple sirups, but on
mixtures, especially those containing small percentages of maple, the
error arising in the determination of the lead number is very marked

. Amer. Chem. Soc., 1906, 28: 1205.

[Cir. 53]

and gives zero or negative results, as indicated by the following com-
parisons of lead numbers on two series of sirups calculated from both
unfiltered and filtered standards.

Comparison of lead numbers on two series of known mixtures, using unfiltered and filtered

standards.

Maple sirup content.

Lead number.

Unfiltered.

Filtered.

Unfiltered.

Filtered.

Per cent.
100

1.073
.438
.133
.042

0.997
.362
.057
— .034

1.521
.673
* .221
.062

1.444
.597
.145
— .013

50

25. . . . .

10

On another lead subacetate solution the standard was obtained in
three ways. First, on the unfiltered blank; second, on the filtered
blank; and, third, on a blank to which 25 grams of a cane sugar sirup
were added prior to the addition of the 25 cc of lead subacetate solu-
tion. The weights of lead sulphate obtained from 10 cc aliquots were
respectively 0.1701 gram, 0.1660 gram, and 0.1685 gram. If the
filtered blank is taken as the standard, one would apparently obtain
more lead from the cane sugar sirup blank than was actually added,
which discrepancy is corrected by the use of the unfiltered blank.
To avoid the possibility of obtaining an incorrect aliquot on the
turbid unfiltered blank, add 5 cc of 10 per cent acetic acid to the
blank flask prior to the addition of the 25 cc of lead subacetate
solution, which insures a clear blank for the determination of the
standard.

Acetic acid should be added only to the blank, since this reagent
dissolves the maple lead precipitate. Otherwise the procedure was the
same as given by Winton with the exception that after addition of
lead subacetate the mixture was allowed to stand three hours prior
to filtering; 2 cc of 20 per cent sulphuric acid were used to precipitate
the lead. The results were calculated by subtracting the weight of
the lead sulphate obtained from 10 cc of the clear filtrate from that
obtained from 10 cc of the acidified blank or standard. The re-
mainder expressed in grams multiplied by 27.325 a equals the lead
number or percentage of lead precipitated by the sirup.

FURTHER STUDY OF KNOWN MIXTURES, USING THE ACID BLANK.

The lead number was determined on four straight sirups, and on
four series of mixtures made by combining with each sirup various
percentages by weight of S (cane sugar sirup, 66 per cent sucrose

« This factor is obtained by dividing the lead factor (0.68312) by the number of
grams of sirup in the 10 cc used (2.5 grams) and multiplying by 100.
[Cir. 53]

content). The first three samples (E, Ohio; F, Vermont; and G,
Canada) were authentic. The fourth sample (H) was unknown, but
was used to illustrate the variation of the lead numbers obtained on
mixtures made from a sirup having a low lead number. All of the
results given in the following tables are on the basis of the acid
blank:

Winton lead numbers on known mixtures, using the acid blank.

Simp.

Lead number^

Maple sirup content.

Actual.

Calculat-
ed.

Appar-
ent.

Actual.

E...

1.424

Per cent.

Per cent.
100
75
50
25
10

100
75
50
25
10

ion

5,)
10

10Q

5)
IT)
11

E-S . . .

1.005
.601
.221
.044

1.322

1.068
.712
.356
.142

70.5
42.2
15.5
3.1

E-S

E-S..

E-S

F.

F-S...

.959
.604
.235
.057

1.521

.991
.661
.331
.132

72.5

45.7
17.8
4.3

F-S

F-S

F-S. .

G ..

G-S

.673
.221
.062

1 073

.761
.380
.152

44.2
14.5
4.0

G-S ..

G-S

II

H-S...

.438
.133
.042

.537
.268
.107

40.8
12.4
3.9

H-S . . .

H-S

These results show conclusively that the lead number thus
obtained is not proportional to the amount of maple sirup present
in a mixture. Theoretically a pure maple sirup, which gives a
copious precipitate when treated in the usual manner, should yield
one- tenth the volume of the original precipitate if it is first diluted
with 90 per cent of inert cane sugar sirup. But in several instances
it was observed that these 10 per cent maple content sirups gave no
precipitate or at most an opalescence, which would be reported as
"no precipitate" or "slight precipitate," and the sirup would be
declared ordinarily to contain little or no maple sirup.

INFLUENCE OF SUCROSE AND LEAD SUB ACETATE ON THE MAPLE

LEAD PRECIPITATE.

As a deduction from these experiments, it was inferred that the
nonproportional result obtained on a mixed maple and cane sugar
sirup was due to the solvent action of the sugar solution which par-
tially inhibited the formation of the maple lead precipitate. Doo-
little and Seeker a judged that this discrepancy was due to a great

«U. S. Dept. Agr., Bureau of Chemistry Bui. 122, p. 198.

[Cir. 53]

excess of basic lead acetate. To determine the relative effect of the
sucrose and the excess of basic lead acetate in the formation of the
maximum maple lead precipitate, five series of determinations were
made, using less lead in each successive series. In the first deter-
mination of each series 25 grams of a pure maple sirup were used.
In the second determination of each series 5 grams of the same pure
maple sirup plus 20 grams of a pure cane sugar sirup were us*ed. In
the third determination of each series 5 grams only of the maple
sirup were used. In the second and third determinations there were
present, therefore, equal amounts of maple sirup, and the difference
in the amount of the precipitate formed was due to the solvent action
of the 20 grams of cane sugar sirup present in the second but omitted
in the third.

Method of Procedure and Results.

Introduce the quantity of sirup, maple or both maple and cane
sugar sirup as indicated in the table, into a 100 cc volumetric flask;
add distilled water, leaving room for subsequent addition of the lead
subacetate solution, which then add in the amount indicated; make
up to the mark, shake well and allow to stand three hours. Filter,
and determine the amount of lead in 10 cc of the clear filtrate by the
usual lead sulphate method. Standardize the lead solution in tne
same way but omit the sirup and add 5 cc of 10 per cent acetic acid
(see p. 3).

The lead subacetate solution was introduced into the flasks from
25, 20, 15, 10, and 5 cc pipettes. In a given series the same amount
was added to each subtest but, since the pipettes were not calibrated
exactly or standardized among themselves, the quantity (25 cc) of
lead solution introduced into A was approximately but not abso-
lutely five times the quantity (5 cc) introduced into E, which ex-
plains the apparent slight discrepancy in the column giving the
amounts of lead added.

Since the flasks were filled with water, leaving only sufficient room
for the addition of the lead subacetate solution, of the strength
specified by Winton, the results are comparable with those of Doo-
little and Seeker, who added smaller amounts of lead by first diluting
the strong solution and then adding 25 cc of the dilute solution.

Each determination was made in duplicate, the average result
only being given. The maximum difference in the weight of the
lead sulphate on duplicates was 0.5 mg and the minimum 0.0 mg;
mean difference on 20 sets, 0.2 mg. x

[Cir. 53]

6

Determinations showing the relative effect of the sucrose and the excess of lead subacetate in
the formation of the maximum maple lead precipitate.

Series. '

Sub-
test.

Maple
sirup.

Cane
sugar
sirup.

Lead
subac-
etate.

Ratio of
lead to
sirup. a

Lead-metal in 100 cc flask.

Lead number.

Added.

Precip-
itated.

Apparent ex-
cess.

Empir-
ical, b

Ac-
tual, c

A

(>

1 3

1 2
1 3

11
1!
11

grams.
25-
5
5

25
5
5

25
5
5

25
5

5

25
5
5

grams.
0
20
0

0
20
0

0
20
0

0
20
0

0
20
0

cc.
25
25
25

20
20
20

15
15
15

10
10
10

5
5
5

1:1
1:1
1:0.2

1:1.25
1:1.25
1:0.25

1:1.66
1:1.66
1:0.33

1:2.5
1:2.5
1:0.5

1:5
1:5
1:1

grams.
1. 1825
1. 1825
1. 1825

.9461
.9461
.9461

.7077
.7077
.7077

.4755
.4755
.4755

.2309
.2309
.2309

grams.
0. 3682
.0342
.0697

.3757
.0417
. 0779

.3497
.0526
.0799

.2849
.0594
.0861

.1441
.0601
.0833

grams.
0. 8143
1. 1483
1.1128

.5704

.9044
.8682

. 3580
. 6551
.6278

.1906
.4161
.3894

.0868
.1708
.1476

percent.
221.1
3, 357. 6
1,596.6

151.8
2, 168. 8
1,114.5

102.4
1.245.4

785.7

66.9
700.5
452.3

60.2

284.2
177.2

1.473

.684
1.394

1.503
.834
1.558

.399.
.052
.598

.140
.188
1.722

.576

1.202
1.666

1.473
.137

B

1.503
.167

c

1.399
.210

D

1.140
.238

.576
.240

E

« Volume (cc) of lead to weight (grains) of total sirup.

b Per cent of lead precipitated by the maple sirup, i. e., the weight of lead in grams precipitated by 100
grams of the maple sirup under conditions given.

c Per cent of lead precipitated by the total sirup, i. e., the weight of lead in grams precipitated by 100
grams of the total sirup under conditions given.

The relative effect of the sucrose and the excess of lead subacetate
iji the formation of the maple lead precipitate may readily be seen by
referring to the following summaries from the main table:

Comparison of empirical lead numbers on subtests 2 and 3 showing differences due to the

solvent action of the sugar.

Empirical lead num-

ber on —

Series.

Lead sub-
acetate
added.

Subtest 2
(5 grams of
maple and
20 grams of

Subtest 3
(5 grams of
maple sirup

Difference.

cane sugar

only).

sirup).

cc.

A

25

0.684

1.394

0.710

B...

20

.834

1.558

.724

C

15

1.052

1.598

.546

D

10

1. 188

1.722

.534

E

5

1.202

1.666

.464

Comparison of empirical lead numbers on series A and E, showing differences due to the
solvent action of an excess of lead subacetate.

Subtest.

Empirical lead num-
ber on —

Difference.

Series A
(25 cc lead
added).

Series E
(5 cc lead
added).

2

0.684
1.394

1.202
1.666

0.518
.272

3

[Cir. 5.3]

Discussion of Results.

It is evident that while both the sucrose and the lead subacetate
had a marked effect, that of the sugar was greater. By reducing the
amount of lead subacetate solution from 25 cc to 5 cc it was not
possible to attain on subtest 2 the empirical lead number 1.473 or
1.503 obtained on the straight maple sirup in tests A-l and B-l,
respectively, which numbers should have been very closely ap-
proached to permit the quantitative use of the Winton lead number.

In the writer's modification, given on page 8, the solvent action
of the sugar appears to be satisfied in preventing the precipitation
of the lead sulphate, which would naturally precipitate on the addi-
tion of the lead subacetate solution subsequent to the addition of
the potassium sulphate solution. The maple lead compound is then
free to precipitate and under the conditions specified appears to give
proportional results.

In the determination of the actual lead number on 25 grams of
the straight maple sirup the maximum number (1.503) was obtained
in series B, in which there was present in the filtrate 151.8 per cent
excess of lead. The corresponding lead number in series C was 1.399
with 102.4 per cent apparent excess of lead. In the latter case
0.7077 gram of lead was added and, using the weight (0.3757 gram)
precipitated in series B as the basis for calculation, there was present
88.4 per cent excess of lead, yet a decidedly low result was obtained.
It would therefore appear that to obtain the maximum precipitation
on straight sirups at least 150 per cent excess of lead should remain
in the filtrate.

When 5 grams only of maple sirup were used, i. e., subtest 3, a
maximum precipitation was obtained in series D, in which an empi-
rical lead number 1.722 was obtained with 452.3 per cent excess of
lead. In E-3 a lead number 1.666 was obtained with 177.2 per cent
excess of lead, which was a slight drop from the previous test and
w,ould further indicate that at least 150 per cent excess of lead should
be present for maximum precipitation.

On the mixed sirup in test D-2 the ratio of lead to sirup was 1:2.5
and an actual lead number 0.238 was obtained with 700.5 per cent
excess of lead. In E-2 the ratio was 1 : 5 and an actual lead number
0.240 was obtained with 284.2 per cent excess of lead. With a reduc-
tion of 416 per cent excess of lead the increase in the actual lead
number is scarcely perceptible, and, from the results obtained on the
straight sirup, it would not seem that a further reduction in the excess
of lead would give a further increase in the actual lead number on
mixed sirups.

With respect to the desired excess of lead it appears that on all
sirups, both straight maple and mixed cane sugar and maple sirups,

[Cir. 53]

8

at least 150 per cent excess of lead is required to obtain the maximum
precipitation and, further, that 250 per cent excess of lead has prac-
tically a negligible effect in preventing the maximum precipitation.

In analyzing a series of unknown sirups it would be impracticable
to ascertain by preliminary trial the desirable amount of lead to be
added and then to introduce these varying amounts into each test;
furthermore, proportional values are not obtained even by varying
the amounts of lead. The modified method, however, as given in
the following section appears to give satisfactory proportional results
on sirups of varying composition.

PROPOSED MODIFICATION.

To overcome the solvent or disturbing action of the sugar, it
occurred to the writer that the addition of a precipitant, such as
potassium sulphate solution, would allow a more complete formation
of the maple lead precipitate and give proportionate results. Sev-
eral series of experiments were made to ascertain the amount of
potassium sulphate which should be added to correct the solvent
action of the sugar, and the following method was adopted:

Transfer 25 grams of the sirup to a 100 cc flask, using about 25 cc of distilled water,0
add 10 cc of potassium sulphate solution (7 grams per liter); then 25 cc of lead sub-
acetate solution of the strength specified by Winton. Make up to the mark, shake
thoroughly and allow to stand three hours. Filter, rejecting the first portion of the
filtrate. Pipette off 10 cc of the clear filtrate into a 250 cc beaker, dilute to 50 cc, add
2 cc of 20 per cent sulphuric acid and 100 cc of 95 per cent alcohol. Let stand over
night; filter off the lead sulphate on an ignited, weighed Gooch crucible, wash with
95 per cent alcohol, dry, ignite at low redness for three minutes in a muffle or over a
burner, taking care to avoid reducing cone of the flame, and weigh. Run a blank in
exactly the same way substituting 25 grams of a pure cane sugar sirup (66 per cent
sucrose content) in place of the sirup to be tested, b Subtract the weight of the lead
sulphate, obtained from 10 cc of the sirup test filtrate, from that obtained from 10 cc
of the cane sugar sirup blank filtrate. The remainder, expressed in grams and
multiplied by 27.325 gives the modified Winton lead number.

The precipitate formed in the blank was very slight, little more
than an opalescence, while in the mixed sirups the volume of pre-
cipitate was proportional and a marked flocculent precipitate was
observed in the 10 per cent maple content sirup. The flasks should
be rotated gently when water is added to make up to mark, otherwise
the sugar solution becomes too weak. When water is floated on the
contents of the flask a slightly increased precipitation of lead sulphate
is produced, which is not redissolved on subsequent agitation.

The lead number's obtained in this way on straight maple sirups are
somewhat higher than by the original method, 1.8 to 3 instead of 1.2

« Freshly boiled distilled water should be used throughout.

& Do not use acetic acid in this blank; acidified blank is suggested for use only with
original Winton method.
[Cir. 53]

to 2.5, but the results obtained on the mixtures are proportional and
more dependence can be placed on a fractional part of a higher con-
stant. The modified lead number was determined on ten authentic
samples a of maple sirup and also on each sample after adding 50 per
cent, by weight, of a cane sugar sirup (66 per cent sucrose content)
with the following results :

Modified lead numbers on authentic samples and mixtures containing 50 per cent of cane

sugar sirup.

Source.

Modified lead number.

Apparent
content of
maple sirup
in 50 per
cent
mixtures.

Actual
on 100
per cent.

Calculated
on 50 per
cent.

Actual
on 50 per
cent.

New York

2.44
2.47
2.74
2.08
2.73
2.30
2.17
2.47
2.99
2.52

.22
.235
.37
.04
.365
.15
.085
.235
.495
.26

1.21
1.20
1.48
1.01
1.36
1.15
1.15
1.26
1.64
1.29

Per cent.
49.6
48.6
54.0
48.6
49.8
50.0
53.0
51.0
54.8
51.2

Vermont.

Do

Massachusetts .

Do

New York

Do

Ohio

Do

New Hampshire. .

Average ., •

2.49

1.245

1.275

51.1

In this work the effect of the addition of cane sirup or brown sugar
sirup, which is very pronounced, has not been considered, only the
determination of the maple content of sirups made by the admixture
of cane sugar sirup. The points which the writer wishes to emphasize
are the use of an unfiltered or acidified blank when following the
original Winton method and the advantage of the proposed modified
method in that it affords proportionate results on mixtures.

« Samples furnished by A. H. Bryan, Sugar Laboratory, Bureau of Chemistry.
[Cir. 53]

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