Vinegar
Analyst, iii, 1878, p. 268; i, 1877, p. 105.
Ann. d’Hyg. et Méd. Lég. 2 sér. t. xii.
Pharm. Journ., Jul. 3, 1875.
Within the last few years the subject of food-adulteration has been so prominently brought before the public that, in many instances, the various State Boards of Health have commissioned their chemists to furnish reports on this subject. These may be found in the annual publications of the same, notably in the volumes issued by the Massachusetts, Michigan, New Jersey, and New York State Boards of Health. It may also be mentioned in this connection that the Sanitary Engineer of New York, the Analyst of London, the Zeitschrift für Untersuchung von Lebensmitteln, Eichstatt, and the Zeitschrift gegen Verfälschung der Lebensmittel, Leipzig, are journals devoted to the consideration of adulterations and the more recent methods employed for their detection.
J. P. B.
Footnotes
A The degrees of temperature given in the text refer to the centigrade Thermometer; their equivalents on the Fahrenheit scale can be obtained by means of the formula:
9/5 C° + 32 = F°.
—Trans.
B The sulphur, usually accompanying the precipitate of sulphide of arsenic, is insoluble in ammonia.—Trans.
C The fusing of the point of the tube is also prevented by platinizing it. The tube is drawn out, its end roughened by filing, and then immersed in solution of bichloride of platinum, so that a drop or two of the fluid adheres. The point, upon heating, now acquires a fine metallic lustre, and by repeating the operation a few times a good coating of platinum is produced both on the exterior and interior of the tube.—Trans.
D The addition of a few drops of solution of bichloride of platinum to the mixture of zinc, water and sulphuric acid is advisable.—Trans.
E The effervescence of the mixture is prevented by slowly adding the arsenical solution to the generating flask. In order to avoid loss of arsenetted hydrogen, the cold dish should be directly applied to the flame even before the introduction of the suspected solution, and its position changed at short intervals, so as to allow the deposit to be formed on different parts.—Trans.
F Owing to the impurities often occurring in zinc, the use of distilled magnesium in Marsh’s apparatus has also been suggested. This metal is now to be obtained in a state of great purity; it is, however, sometimes contaminated with silicium, which body likewise gives rise to a metallic deposit, but one that is readily distinguished from arsenical spots by its insolubility in nitric acid, aqua regia, and in hypochlorite of soda. The presence of magnesium causes the precipitation of the non-volatile metals possibly contained in the fluid tested for arsenic.—Trans.
GThe omission in the text of Reinsch’s test should be supplied. This test is based upon the fact that when solutions of arsenious acid or an arsenide are acidulated with hydrochloric acid and boiled with metallic copper, the latter becomes covered with a film consisting largely of metallic arsenic: it is extensively employed in chemico-legal examinations. The materials to be examined are completely disintegrated by boiling with hydrochloric acid, and the fluid filtered. Some pure copper gauze or foil, having a polished surface, is then immersed in the boiling solution, and notice taken of the formation of a grey deposit. If a coating be formed, fresh pieces of the metal are added, so long as they become affected. The copper is then withdrawn from the solution, thoroughly washed with water, and dried, either by means of the water-bath or by pressing between bibulous paper. It is next introduced into a dry tube, and heated over a spirit lamp. The arsenic present volatilizes and is oxidized to arsenious acid which forms a deposit, consisting of octahedral crystals, on the cold part of the tubes. These are subsequently tested by means of the reactions distinctive of arsenious acid. It need hardly be added that the absolute purity of both the hydrochloric acid and of the copper is to be carefully established. The deposit obtained in the above operation was formerly regarded as pure arsenic, but it has been proved to be an alloy consisting of 32 per cent. arsenic, and 68 per cent. copper. Reinsch’s test possesses the advantage of requiring but little time for its execution, of being applicable to complex organic mixtures, and of effecting the detection of a very minute trace of the poison.—Trans.
H Ferrocyanides and ferricyanides—non-poisonous compounds—likewise, evolve hydrocyanic acid when distilled with a strong acid. Their presence is indicated by stirring a small portion of the materials with water, filtering the fluid, acidulating the filtrate with hydrochloric acid, and testing two portions: one with sesquichloride of iron, the other with protosulphate of iron. If either of the above salts be present, a blue precipitate is produced.—Trans.
I Baryta and strontia dissolve in alcohol, but only when they are anhydrous and the alcohol is absolute, which is not the case here.
J The so-called “chloride of lime” is probably either a mixture of chloride and hypochlorite of calcium or an oxydichloride of the metal; “Eau de Javelle” is the corresponding potassium compound.—Trans.
K If an insoluble residue remains by the treatment with nitric acid, it may consist of tin. In this case, it is dissolved in aqua regia, the metal precipitated by immersing a plate of zinc in the solution and then re-dissolved in boiling hydrochloric acid. Upon adding chloride of gold to the solution so obtained, a purple precipitate is formed. Sulphuretted hydrogen produces a brown precipitate, soluble in sulphide of ammonium, in presence of tin.
L Colchicine, picrotoxine and digitaline.
M The necessity of decanting etherial and other solutions is advantageously obviated by the use of a pipette.—Trans.
N Cinchonine, when sublimed, condenses in minute brilliant needles.—Trans.
O An alkaline solution of tartrate of copper, employed in the examination of sugar, urine, and wine.—Trans.
P Most of the substances here enumerated are rarely, if ever, used for the adulteration of flour in this country. The analyst should, however, give attention to the examination for such salts as alum, sulphate of copper, plaster, kaolin, etc.—Trans.
Q It may be added, as a distinguishing property, that granules of potato starch, when viewed in polarized light by aid of a Nicol’s prism, present a well-defined black cross, corresponding to the hilum; wheaten-starch fails to exhibit this phenomenon.—Trans.
R If the detection of alum in bread is desired, a portion of the crumb is incinerated in a platinum dish, the ash is treated with concentrated hydrochloric acid, the filtered solution evaporated to dryness, and the residue treated with hydrochloric acid, which now leaves the silica present undissolved. The acid solution is then filtered, nearly neutralized with carbonate of soda, and an alcoholic solution of potassa added in excess. The earthy phosphates present are now precipitated, alumina remaining in solution. The use of aqueous potassa in this case—as well as in the case mentioned in the text—is not advisable, as it is seldom entirely free from alumina. Upon slightly acidulating the alkaline filtrate with hydrochloric acid, and adding carbonate of ammonia, the alumina present is precipitated, and may be dried and tested by means of the reaction with nitrate of cobalt before the blow-pipe.
In the quantitative estimation of alumina, the phosphoric acid usually present in the precipitate should be removed. This is done by dissolving the precipitate in nitric acid and immersing a piece of metallic tin in the boiling solution: phosphoric acid is thrown down as a mixture of stannic oxide and phosphate, and the alumina is then precipitated as usual by carbonate of ammonia.—Trans.
S According to Wagner, if the ash, obtained by incinerating the adulterated bread, is washed with water, shining spangles of metallic copper are separated.—Trans.
T The British Society of Public Analysts regard the following as the minimum proportions of constituents in unadulterated milk:
| Fat | 2.5 | per cent. |
| Solids, not fat | 9. | ″ ″ |
| Total | 11.5 | ″ ″ |
| Water | 88.5 | ″ ″ |
—Trans.
U Fragments of nerves, and other organic structures, are frequently observed in this examination.—Trans.
V Cotlini (Ann. du genie civil, No. 3, 1873) states that the following reactions occur when artificially colored wines are heated with potassa:
| Pure wine | no precipitate | greenish hue | |
| Elderberry | violet | ″ | |
| Beet-sugar | red | ″ | |
| Logwood red | violet-red | ″ | |
| Privet | violet-blue | ″ | |
| Turmeric | light-blue | ″ |
According to M. de Cherville (Quar. Jour. Sc.), a bright violet coloration is produced in the above test, if litmus be present.
Fuchsin is separated by treatment with subacetate of lead and addition of amylic alcohol (Jour. de Ph. et de Ch. Mar. 1873).
—Trans.
W Tralles alcoholmeter is almost exclusively employed in this country.—Trans.
X Fresh gluten, gum arabic, and caseine also cause the blue coloration.—Trans.
Y Menstrual blood is recognized by the presence of epithelial cells.—Trans.