Transcriber’s notes:
Italics in the original work are here represented _between underscores_,
bold face text is represented =between equal signs=. Small capitals from
the original work are here represented by ALL CAPITALS.
More Transcriber’s Notes may be found at the end of this text.
Detection of the Common
Food Adulterants
BY
EDWIN M. BRUCE
INSTRUCTOR IN CHEMISTRY, INDIANA STATE NORMAL SCHOOL
LONDON
ARCHIBALD CONSTABLE & CO., LTD.
10 ORANGE STREET, LEICESTER SQUARE, W.C.
1907
_Copyright, 1907_
BY D. VAN NOSTRAND CO.
PREFACE
Because of the recent agitation of the pure food question throughout the
country, health officers, food-inspectors, and chemistry teachers and
students are constantly called upon to test the purity of various foods.
And this usually involves nothing more than making simple qualitative
tests for adulterants. In view of the fact that there is now no text or
manual devoted exclusively to the qualitative examination of foods, this
little book is offered to those who are interested in this work.
Its aim is to bring together in one small book the best and simplest
qualitative tests for all the common food adulterants. It contains a
brief statement of the adulterants likely to be found and the reason for
their use. It is hoped that it will be specially valuable to chemistry
teachers in furnishing excellent supplementary work in qualitative
analysis. But it is hoped that it will find its greatest usefulness in
contributing something toward the great pure food reform.
It is impossible to make due mention of all the sources from which these
various tests have been collected, but where possible, the author’s name
has been associated with the test.
TERRE HAUTE, IND.
_March 25, 1907._
TABLE OF CONTENTS
CHAPTER I PAGE
DAIRY PRODUCTS 1
=Milk=--Adulterations of--Coloring matters--Annatto--Caramel--
Coal-tar colors--Preservatives--Formaldehyde--Boric acid--Salicylic
acid--Gelatin--Starch.
=Butter=--Adulterations of--Coloring matter--Preparation of sample
--Annatto--Coal-tar colors--Saffron--Turmeric--Marigold--Process or
renovated butter--Oleomargarine--Cottonseed oil.
CHAPTER II
MEATS AND EGGS 8
Adulterations of--Fresh and smoked--Preservatives--Potassium
nitrate--Boric acid--Sulfurous acid--Salicylic acid--Benzoic acid--
Canned--Preservatives (same as those of fresh and smoked meat)--
Heavy metals--Coloring matter (see under sausages, etc.)--Fish,
salt, dried and oysters--Preservatives--Boric acid (same under
smoked and fresh meat)--Coloring matter--Aniline red and cochineal-
carmine--In sausages, chopped meat, preparations and corned meat--
Starch--In sausages, deviled meat and similar products--Diseased
meats--Horse-flesh in sausages and in mince-meat.
=Eggs=--Test for age.
CHAPTER III
CEREAL PRODUCTS 16
=Flour=--Adulteration of--Alum--Copper sulfate--Substituted flours
--General test--Corn meal in wheat flour--Wheat flour in rye flour
--Ergot in rye flour.
=Bread=--Adulterations of--Alum--Copper sulfate.
=Ginger Cake=--Adulterations of--Stannous chlorid.
CHAPTER IV
LEAVENING MATERIALS 20
=Baking Powders=--Adulterations of--Tartaric acid (free or
combined)--Tartaric acid (free)--Sulfates (calcium, etc.)--Gypsum--
Ammonium salts--Alum.
=Cream of Tartar=--Adulterations of--Tartaric acid (free or
combined)--Aluminium salts--Ammonia--Earthy materials.
CHAPTER V
CANNED AND BOTTLED VEGETABLES 24
Adulterations of--Preservatives--Preparation of sample--
Formaldehyde--Sulfurous acid and the sulfites--Salicylic acid--
Saccharin--Benzoic acid--Coloring matter--Cochineal--Coal-tar dyes
--Copper salts--In green pickles, beans, peas, etc.--Turmeric--In
mixed pickles--Heavy metals (other than copper, same as under
meats)--Soaked vegetables--Peas, beans and corn--Alum--In pickles--
Examination of the can or box.
CHAPTER VI
FRUITS AND FRUIT PRODUCTS 33
Adulterations of--Preservatives--Preparation of sample--Salicylic
acid--Benzoic acid--Saccharin--Coloring matter--Coal-tar dyes--
Cochineal--Acid magenta--Apple juice in jellies made from small
fruits--Detection (see test for starch)--Starch--In jellies, jams
and such products--Gelatin--In jellies--Agar agar--Heavy metals--
Arsenic.
CHAPTER VII
FLAVORING EXTRACTS 42
=Lemon Extract=--Lemon oil--Citral--Oil of citronella--Tartaric or
citric acid--Methyl alcohol--Coloring matter--Turmeric--Coal-tar
colors.
=Vanilla Extract=--Adulterations of--Preliminary test--Alkali--
Foreign resins--Caramel--Tannin--Coumarin.
CHAPTER VIII
SACCHARINE PRODUCTS 49
=Honey=--Adulterations of--General observations--Cane sugar--
Commercial glucose syrup--Gelatin.
=Maple Syrup=--Adulterations of--General examination--Glucose.
CHAPTER IX
SPICES 51
=Mustard=--Adulterations of--Flour--Coloring matter--Turmeric--
Martius yellow or analogous coal-tar coloring matter--Cayenne
pepper.
=Pepper=--Adulterations of--General test--Ground olive stones--
Cayenne pepper.
CHAPTER X
VINEGAR 55
Adulterations of--Preparation of sample--General observations--
Free mineral acids--General tests--Sulfuric acid--Hydrochloric acid
(free)--Malic acid--Coloring matter--Caramel--Coal-tar colors--In
wine vinegar--Free tartaric acid--In wine vinegar.
CHAPTER XI
FATS AND OILS 60
=Lard=--Adulterations of--Cottonseed oil--Cottonseed stearin--Beef
stearin.
=Olive Oil=--Adulterations of--General test--Cottonseed oil--Peanut
oil--Sesame oil--Rape oil.
CHAPTER XII
BEVERAGES 65
=Coffee=--Adulterations of--General test--Coloring matter--
Imitation coffee beans--Chicory.
=Tea=--Adulterations of--Foreign leaves--Exhausted tea leaves--Lie
tea--Facing--Catechu.
PURE FOOD TESTS
CHAPTER I
DAIRY PRODUCTS
MILK
Milk is adulterated by watering, removing the cream or by adding some
foreign substance. Formaldehyde, boric acid or salicylic acid may be
added to preserve the milk. Annatto, caramel or some coal-tar dye is
added, sometimes to improve the color of the milk, and at other times to
cover up traces of watering. Gelatin and starch are added for the same
purpose, though they are not frequently used.
ARTIFICIAL COLORING MATTER
ANNATTO
Add acid sodium carbonate to a sample of the milk until it shows a
slight alkaline reaction. Immerse a piece of filter-paper and leave it
in for 12 or 15 hours. If annatto is present, there will be a
reddish-yellow stain on the paper.
CARAMEL
_Leach’s Method._--Warm 150 cc. of the sample and add 5 cc. of acetic
acid, then continue heating it nearly to the boiling point, stirring
while it is being heated. Separate the curd by gathering it with the
stirring rod or by pouring through a sieve. Press out all the whey from
the curd and macerate the latter for several hours (10 to 12 hours) in
50 cc. of ether. It is best to do this in a tightly corked flask,
shaking it frequently. If the milk was uncolored or colored with annatto
the curd when thus treated will be white. If the curd is a dull brown
color caramel was probably used to color the milk. Confirm its presence
by shaking a portion of the curd with concentrated hydrochloric acid
(sp. gr. 1.20) and gently heating. If the acid solution turns blue while
the curd does not change its color, caramel was used to color the milk.
(Remember that the ether-extracted curd must be brown.)
COAL TAR COLORS
_Lythgoe’s Method._--Mix in a porcelain vessel about 15 cc. each of the
sample of milk and hydrochloric acid (sp. gr. 1.20) and break up the
curd into coarse lumps by shaking gently. If an azo-color was used to
color the milk this curd will be pink, but the curd of normal milk will
be white or yellowish.
STARCH
The presence of starch in milk may be detected by heating a small
quantity of the milk to boiling. When it has cooled add a drop of iodin
in potassium iodid, and if starch is present there will be a blue
coloration.
GELATIN
_A. W. Stokes’ Method._--Dissolve 1 part by weight of mercury in 2 parts
of nitric acid (sp. gr. 1.42). Add 24 times this volume of water. Mix
equal volumes (about 10 cc.) of this reagent and the milk or cream,
shake well and add 20 cc. of water. Shake again and, after standing 5
minutes, filter. When a great quantity of gelatin is present the
filtrate will be opalescent instead of perfectly clear. To a little of
this filtrate in a test tube add the same volume of a saturated aqueous
solution of picric acid. If much gelatin is present a yellow precipitate
is produced, smaller amounts produce a cloudiness. If the filtrate is
perfectly clear gelatin is absent and picric acid may be added without
producing any noticeable effect.
PRESERVATIVES
FORMALDEHYDE
_Hehner’s Sulfuric Acid Test._--Put 10 cc. of the suspected milk in a
wide test tube and pour carefully down the side of the inclined tube
about 5 cc. commercial sulfuric acid so that it forms a separate layer
at the bottom. A violet coloration at the union of the two liquids
indicates the presence of formaldehyde. If the commercial acid is not
available, the pure acid may be used, but a few drops of ferric chloride
must be added. Sometimes the charring effect of the acid makes it
advisable to use the following test:
_Hydrochloric Acid Test._--2 cc. of 10 per cent ferric chloride is added
to one liter of commercial hydrochloric acid sp. gr. 1.2 (or any
quantity in this proportion). To 10 cc. of this mixture add 10 cc. of
the milk to be tested. Heat the mixture slowly nearly to the boiling
point, in an evaporating dish, but agitating it all the while to prevent
the curd collecting in one mass. If formaldehyde is present, there will
be a violet coloration. It is said that by this test as small a
quantity of formaldehyde as 1 part in 250,000 parts of milk can be
detected. It is not so sensitive in sour milk.
BORIC ACID
_Turmeric Paper Test._--Incinerate some of the milk, and acidulate the
ash with a very few drops of dilute hydrochloric acid and afterwards
dissolve it in a few drops of water. Place a strip of turmeric paper in
this solution for a few minutes, then remove and dry it. If boric acid
either free or combined is present, the turmeric paper will be turned to
a cherry-red color.
_Another way of making this test._--U. S. Dep. of Agr., Div. of Chem.,
Bul. 65, p. 110: Make strongly alkaline with lime water, 25 grams of the
milk, and evaporate to dryness on the water bath. Destroy the organic
matter by igniting the residue. Dilute with 15 cc. of water and acidify
with hydrochloric acid. Then add 1 cc. of the concentrated acid. Dip a
piece of delicate turmeric paper in the solution; and if borax or boric
acid is present, it will have a characteristic red color when dry.
Ammonia changes it to a dark blue green, but the acid will restore the
color.
(Turmeric paper may be prepared by dipping pieces of smooth, thin filter
paper in a solution of powdered turmeric in alcohol.)
SALICYLIC ACID
(This is not often used as a preservative of milk.)
_Leach suggests the following method for its detection._--Dissolve one
gram of mercury in 2 grams of nitric acid (sp. gr. 1.42) and then add to
the solution the same volume of water. Add 1 cc. of this reagent to 50
cc. of the milk to be tested, and shake and filter. The perfectly clear
filtrate is shaken with ether and the ether extract evaporated to
dryness. Then add a drop of ferric chlorid solution, and a violet color
will be produced if salicylic acid is present.
BUTTER
Butter is often colored with annatto, saffron, turmeric, marigold or
coal-tar colors. By a certain process, stale or old butter is sometimes
worked over and made to appear fresh for a time. This is sold under the
name of “process” or “renovated” butter. Foreign fats like cottonseed
oil, sesame oil, or oleomargarine may be substituted for or added to
pure butter.
COLORING MATTER
_Martin’s Test._--Add 2 parts of carbon bisulfid, a little at a time and
with frequent shaking, to 15 parts of alcohol. Shake 25 cc. of this
solution with 5 grams of the butter, and let stand for some time. The
carbon bisulfid dissolves out the fatty matter and settles to the
bottom. The alcohol remains on top and will dissolve out any artificial
colors that may be present. If only a little coloring matter is present
use more of the butter.
ANNATTO
Evaporate a portion of the extract to dryness and add sulfuric acid to
the residue. If annatto is present a greenish-blue color forms. Should a
pink tint result the presence of a coal-tar color is to be suspected.
COAL-TAR COLORS
These colors will dye wool or silk if pieces of the fiber are boiled in
the diluted alcoholic extract, which has first been acidified with
hydrochloric acid. The normal butter coloring matter will not dissolve
when thus treated.
_Geisler’s Method._--To a few drops of the clarified fat on a porcelain
surface, add a very little fullers’ earth. If a pink to violet-red
coloration is produced in a short time the presence of an azo-color is
indicated.
SAFFRON
When saffron is present, nitric acid colors the alcoholic extract green,
and hydrochloric acid colors it red.
TURMERIC
Add ammonia to the alcoholic extract, and if it turns brown it indicates
the presence of turmeric.
MARIGOLD
Add silver nitrate to the extract, and if it turns black the presence of
marigold is indicated.
PROCESS OR RENOVATED BUTTER
Heat a little of the suspected butter in a spoon or dish, and if it is
process butter it will sputter, but not foam much. Make the test also
with some butter known to be pure and fresh.
_Hess and Doolittle Test._--Melt some of the butter (say 40 grams) at
about 50° C. If the butter is pure and fresh the melted fat will clear
up almost as soon as it is melted, while the fat of process butter
remains turbid for quite a while. After most of the curd has settled,
decant as much as possible of the fat. Pour the remainder on a wet
filter. Add a few drops of acetic acid to the water that runs through
from the filter, and boil. If it was ordinary butter this filtrate will
become milky, but if process butter a flocculent precipitate will form.
OLEOMARGARINE
Immerse a test tube, containing some of the filtered fat, in boiling
water for 2 minutes. Make a mixture of 1 part glacial acetic acid, 6
parts ether, and 4 parts alcohol. Add to 20 cc. of this mixture in a 50
cc. test tube, 1 cc. of the heated fat which may be transferred by means
of a hot pipette. Stopper the tube and shake it well. Immerse in water
at 15° or 16° C. Pure butter when thus treated remains clear for quite a
while. There will be only a very little deposit after standing an hour,
but oleomargarine gives a deposit almost immediately, and in a few
minutes there will be a copious precipitate.
When the oleomargarine in butter is in about the proportion of 1 : 10,
it will not separate much short of 15 minutes.
COTTONSEED OIL
The presence of this oil may be detected by Halpen’s test, which is
given under lard, page 60.