CHEMISTRY.
Fraudulent uses of Sulphuric J3cid.—ByH. Letheby, M.B., London,
Lecturer on Chemistry at the Medical College of the London Hospital.
—Sulphuric acid and the sulphates are not uncommonly employed as
sophisticating agents; for example, alum and sulphuric acid are used
for the purpose of increasing the acidity of wines and vinegar ; sulphu-
ric acid is employed in the manufacture of a saccharine compound,
which is used in the adulteration of cane sugar ; and alum, plaster
of Paris, and sulphate of copper are frequently resorted to for the pur-
pose of whitening and increasing the sponginess of bad bread. All these
adulterations are matters of very serious moment both to you and the
public,and the discussion of them is, in my opinion, very properly
suited to this course of lectures. I shall, therefore, direct your atten-
tion to them in a very pointed manner.
Ml the Vinegars of English commerce contain free sulphuric acid,
inasmuch as the vinegar manufacturers are permitted by law to employ
a certain portion, viz : the one-thousandth part by weight of oil of
vitriol, for the purpose of checking the putrefaction to which the
gluten of the liquid is subject: but, as Dr. Ure very properly remarks,
“ this is a miserable shift, or pretended necessity, in the present ad-
vanced state of organic chemistry- It offers, besides, an easy source of
fraud, since neither the retailers nor consumers of the article are com-
petent to distinguish how much of the sourness is derived from the mild
fermented acid, and how much from the corrosive mineral. All the
pickles in which our bourgeoisie so much delight are polluted by the
same sophistication. Not long ago,” continues Dr. Ure, “a sample of
vinegar was submitted to me for examination, said to be that supplied
by contract to the British Navy. I found it to contain little more
than half the fair amount of proof vinegar, with much gluten, and a
copious supplement of oil of vitriol.” Here, also, is a sample ofcheap
vinegar, which I have just obtained from one of the retailers in this
neighborhood, and you will notice that it yields a copious precipitate
with a soluble salt of baryta; it contains, in fact, as much as 0-fi5 per
cent, of sulphuric acid, and a fluid ounce of it yields very neatly nine
grains and a half of sulphate of baryta, in place of one grain and four-
teen hundredths which are allowed by law.
On the Continent, also, manufacturers are accustomed to adulterate
vinegar, and many varieties of low red wines, with alum or sulphuric
acid ; and the fraud has become so serious, that chemists have thought
it necessary to inquire into the matter, in the hope of being able to
point out a ready mode of detectingthe imposition. To this end Orfila
directs that the suspected liquid should be agitated with ether; and,
after standing for a short time, the etherial solutionis to be decanted
and tested for free sulphuric acid. It does not appear, however, that
this mode of proceeding is a very satisfactory ■ one; for, as I have
already informed you, upon the authority of Dr. Christison, ether will
not remove sulphuric acid from an aqueous solution. Guibourt, in
fact, has put this to the test of actual experiment in the case of one
of the liquids in question, and he has drawn from Orfila an admission
that ether will only take up a trace of the poison. Lassaigne, also,
states that, in an examination conducted by MM. Ossian Henri, Bayard,
and himself it was not possible to separate, by the action of sulphuric
ether, four or five-thousandths of sulphuric acid added to red wine,
and, consequently, that this method of operating would not answer for
the detection of the impurity.
In the London Pharmacopceia, it is directed that the quantity of sul-
phate of baryta precipitated from a fluid ounce of vinegar by the addi-
tion of a soluble salt of baryta should not exceed 1.14 grains. But this
rule, however applicable it may be to the composition of malt vinegar,
cannot be applied either to wines, or the vinegars obtained therefrom;
for grape juice contains very variable proportions of alkaline and
earthy sulphates,—salts which will be sure to vitiate the results of the
inquiry. It is necessary, therefore, under these circumstances, to pro-
ceed in a different manner.
MM. Lassaigne, Ossian Henri, and Bayard, inform us that they have,
after many failures, been enabled to decide on a re-action, which is so
delicate, that it will discover the presence of a one-thousandth and a
half of free sulphuric acid in red wine. They say that when a piece
of paper which has been touched with pure wine is dried at a gentle
heat, the spotted portion is unaltered ■ whereas, paper which has been
moistened with wine, to which a very small quantity of sulphuric acid
has been added, reddens, and becomes brittle and friable between the
fingers, when slightly rubbed, before the white paper becomes at all
coloured.
Pure wine, to which nothing has been added, leaves by spontaneous
evaporation a violet blue spot; whereas, wine to which a very small
quantity of sulphuric acid has been added, (two to three thousandths)
gives by drying a rose-colored spot.
On examining into the sensibility of this simple process, the authors
found that they were enabled to detect, by its means, one thousandth
of sulphuric red wine.
The paper most proper for the experiment is common glazed paper,
containing starch or fecula. This kind of paper is well known in
commerce, and it is easy to discover it by the blue color which it as-
sumes when moistened with an aqueous solution of iodine.
Now, although the re-action is a very delicate one, yet I prefer to
operate in the following manner. Take a given portion of the sus-
pected fluid (wine or vinegar,) evaporate it in a water-bath until it ac-
quires a syrupy consistency, then treat it with strong spirit of wine,
filter it; and precipitate the sulphuric acid contained therein by means
of chloride of barium and a little nitric acid. In the course of this
operation the alcohol will take up the free sulphuric acid, and will
leave the neutral sulphates untouched.
Another, but not equally successful mode of operating is the follow-
ing. Take two equal portions of the suspected liquid. Precipitate the
sulphuric acid contained in one of them, and weigh the product. Eva-
porate the other portion to dryness, ignite it, re-dissolve the residue
in water, filter it, and precipitate as before. The weight of this pro-
duct indicates the amount of combined sulphuric acid present, while
the weight of the former represents the entire quantity of acid (free
and combined) which existed in the liquid. Upon subtracting, there-
fore, the weight of the one from that of the other, we can easily de-
termine how much sulphuric acid had been fraudulently added to the
liquid.
Again : Bread is often adulterated with metallic and earthy sulphates
for the purpose of making it look white and spongy. Upon the Con-
tinent, especially in the north of France and in Belgium, public atten-
tion has been long called to the fact, that bakers are accustomed to
employ a solution of blue vitriol (sulphate of copper) for this purpose ;
and M. Kuhlman, formerly Professor of Chemistry, at Lille, has collect-
ed a great number of facts which bear upon this subject. They were
published under the direction of the Central Council of Salubrity of
the Department du Nord; and although I think it right to allude'to
them here, yet I shall postpone their consideration until we come to
treat of the metal which constitutes the chief ingredient of the poison.
From Kuhlman’s researches it appears, that sulphate of copper exerts
a very energetic and peculiar action on the fermentation of bread.
He states that the addition of one grain of this salt to three pounds of
dough will cause it to rise to a much greater extent than it would
otherwise do, and thereby make the bread look white and more ve-
sicular.
Alum is known to operate upon dough in a similar manner ; for {<it
keeps water and rises well,” as bakers express it, and so enables them
to set off a very inferior and otherwise unsaleable flour. In the “En-
cyclopaedia Britannica,” and in the Dictionaries published by Dr. Ure,
I find the following statement:
“ In London, where the goodness of bread is estimated entirely by its
whiteness, it is usual with those bakers who employ flour of an infe-
rior quality, to add as much alum as common salt to the dough ; or, in
other words, the quantity of salt added is diminished one half, and the
deficiency supplied by an equal weight of alum. This improves the
look of the bread very much, rendering it whiter and firmer.” “Now,”
says Dr. Urie, “we may hence infer, that the full allowance here
assigned of two and a quarter pounds of alum for every two pounds
and a quarter of salt, will be adopted in converting a sack of flour into
loaves. But as a sack of flour weighs 280 pounds, and furnishes, on an
average, 80 quartern loaves, we have 2| pounds divided by 80,—that is,
197 grains as the quantity of alum present in a quartern loaf. And as
I need hardly tell you, it is a very serious thing for a gentleman or
lady of sedentary habits, or infirm constitution, to have the digestive
process daily vitiated by damaged flour, whitened with 197 grains of
alum per quartern loaf. Acidity of stomach, indigestion, flatulence,
headaches, palpitation, costiveness, and urinary calculus, may be the
probable consequences of the habitual introduction of so much acidu-
lous and acescent matter.”
My own experience is quite confirmatory of another observation
made by Dr. Ure, who says, “I have made many experiments on
bread, and have found the proportion of alum very variable. Its quan-
tity seems to be proportional to the badness of the flour; and hence,
when the best flour is used, no alum need be introduced.
Plaster of Paris is another agent which is sometimes used for the
sophistication of bad flour. I here show you a specimen of ship-
biscuit, furnished by a cheap baker to a trading captain. It contains
5-5 per cent, of sulphate of lime, which has, doubtless, been introduced
far the purpose of increasing the weight and improving the appearance
of a bad article.
All these adulterations may be recognized by digesting the bread
after it has become very stale, in distilled water, and testing the solution
with nitric acid and baryta for sulphuric acid. Good bread scarcely
affords a cloudiness with this re-agent, and the precipitate so obtained
is too small to be weighed. Again, the last-named adulteration may
be discovered by igniting the bread and weighing the residue. Good
flour or bread will not yield more than two per cent, of ash, the greater
portion of which is soluble in about ten drops of water.
The last point to which I shall direct your attention before I leave
this subject, is the fact, that cane sugars are frequently adulterated with
a low kind of saccharine product, obtained by the action of dilute sul-
phuric acid on starch. This sugar, which is identical in composition
with grape sugar, is recognized by its granular or powdery appearance.
In fact, it does not possess a crystalline structure ; and hence it is devoid
of that sparkling character which is possessed by cane, maple, and beet
root sugars. I am not prepared to tell you that the substance in question is
positively hurtful to the human body, but I am in a condition to say,
that the purpose to which it is commonly applied is injurious to the
fair dealer, and is a gross fraud upon the public. Several chemical
reactions have, from time to time, been referred to as a means of distin-
guishing the presence of glucose in the sugars of commerce, but in my
opinion there are but two of them which possess any practical value:—
1st. It was noticed by Mr. Moore, and his observation has been veri-
fied by Chevalier and others, that starch or granular sugar acquires a
deep brown color when it is boiled with liquor potassae, a reaction
which is not manifested by any other species of saccharine matter. To
employ this test, therefore, you take about ten grains of the suspected
sugar, and heat it in a drachm of liquor potassae; if the liquor acquire
a deep coffee brown color, it indicates the presence of this adulterating
agent.
The second reaction was first noticed by M. Trommer. It is
dependent on the property which glucose or starch sugar has of reducing
the hydrated oxide of copper; and, to make this reaction manifest, you
proceed as follows:—Take about ten grains of the suspected sugar, and
pour upon it a liquid consisting of six drops of a saturated solution of
sulphate of copper, and 3ij. of liquor potassae. Heat this mixture in a
test tube ; and, if granular or starch sugar be present, the solution will
instantly acquire a bright orange color at the point where the flame
touches the tube ; and gradually, as the heat is propagated through the
liquor, the whole contents of the tube will change color, and ultimately
become of a deep brown tint.
Starch sugar, also, frequently contains a considerable portion of
plaster of Paris, the residue of the materials employed in its manufac-
ture ; hence, if you digest such a sugar in strong alcohol, the saccharine
matter will be taken up, and the sulphate of lime left behind in the form
of a white powder.
By adopting one or other of lhese means you will have no difficulty
in discovering the fraud in question.—Med. Times.