(b) METHYL-VIOLET METHOD.

Add to 5 cc of vinegar 5 or 10 cc of water; after mixing well, add 4 or 5 drops of an aqueous solution of methyl-violet (one part of methyl-violet 2B in 10,000 parts of water). The occurrence of a blue or green color indicates the presence of a free mineral acid.

16. Determination of Free Mineral Acids.

(a) HILGER'S METHOD.

Exactly neutralize 20 cc with half-normal alkali, using sensitive neutral litmus paper as indicator. Evaporate to one-tenth of its volume in a porcelain dish, add a few drops of methyl-violet (see sec. 15, preceding), dilute with 3 or 4 cc of water if necessary to secure a clear solution, bring to boiling, and titrate with half-normal sulphuric acid until a green or blue color begins to appear. The difference, in cubic centimeters, between the half-normal alkali and the acid added, multiplied by the factor 0.1225, expresses the percentage of mineral acid present in terms of sulphuric acid (H2SO,).

(b) HEHNER'S METHOD.

To a weighed quantity of the sample add excess of tenth-normal alkali, evaporate to dryness, incinerate, and titrate the ash with tenth-normal acid, using methyl-orange as indicator. The difference between the number of cubic centimeters of alkali added in the first place and the number of cubic centimeters of acid needed to titrate the ash represents the free mineral acid present.

17. Reducing Sugar After Inversion.

Determine after inversion as directed under "XIII. Wine," page 87, except that it is not necessary to evaporate to remove alcohol.

18. Polarization.

Polarize in a 400 mm tube, preparing solution as directed for reducing sugars, under "VI. General Methods," page 40.

19. Detection of Dextrin.

Dextrin is often found in glucose vinegar, and is precipitated from the concentrated vinegar upon addition of three or four volumes of strong alcohol; the precipitate may be identified by its physical properties and the color reaction with iodin solution. Dextrin is generally present.

20. Detection of Coloring Matters.

The principal coloring matter used for tinting imitation vinegars in America is caramel. To detect this use Amthor's method as given under XV. Distilled Liquors," page 101.

A further test for caramel may be made by boiling the aqueous solution of a portion of the precipitate obtained by Amthor's method, with Fehling's solution; caramel has a reducing action.

In the case of wine vinegars, a test for foreign red colors may be made according to the methods given under "XXVIII. Coloring Matter," page 190.

21. Lead Acetate Precipitate.

Add a few drops of neutral lead acetate to 10 cc of a vinegar. Failure to obtain a precipitate proves that it is not a cider vinegar.

22. Detection of Foreign Pungent Materials.

Exactly neutralize a portion of the vinegar (the residue from determination of total acidity may be used), evaporate part of the water, and test the concentrated solution by taste for pungent substances; agitate the liquid with ether in a separatory funnel, remove and evaporate the ethereal layer, and taste the residue. The identification of the specific substance is rarely possible.

23. Heavy Metals.

Evaporate from 200 to 500 cc to dryness. In case of cider, malt, and other vinegars rich in solids, add a little sodium hydroxid and potassium nitrate and incinerate. Dissolve the ash thus obtained, or the solids themselves, and proceed as directed under “IX. Canned Vegetables," page 61.

24. Detection of Preservatives.

Proceed as directed under "XXVII. Food Preservatives," page 179.

7328-No. 107-07-9

XVII. METHODS FOR THE ANALYSIS OF MEAT AND MEAT

PRODUCTS.

MEAT.

1. Identification of Species.-Provisional.

The percentage of glycogen, added to the percentage of reducing sugar, is often of value in detecting horse meat. Certain results obtained in the examination of the fat also afford valuable data. Among the factors which are of value for this purpose may be mentioned the iodin number, melting point, congealing point, index of refraction, and to a less extent the specific gravity, acetyl number, and Maumené value. The meat from embryonic animals and from animals killed before they are suitable for food may often be detected by its moist, clammy nature and high water content. The subject of the determination of the species of animal from which meat is taken is well treated in works on meat inspection and is not discussed here.

2. Injurious and Poisonous Products."-Provisional.

The ordinary foods of man are liable to become unwholesome or poisonous from any of the following causes: (1) Trichinæ in pork, (2) metals, and (3) bacterial products.

(a) TRICHINÆ.

Examine immediately for trichinæ pork, or sausage containing pork, which has caused sickness.

(b) POISONOUS METALS.

Examine for arsenic, antimony, tin, lead, copper, and zinc. For the determination of these metals proceed as directed under " IX. Canned Vegetables," page 61.

(c) BACTERIAL PRODUCTS.

As bacteria are the most common cause of poisonous meat, the examination should primarily be made from that point of view. Given a poisonous meat, the first procedure is to examine for trichinæ. If they are not found, the bacteriological examination should next be undertaken and the chemical examination reserved until the last.

The bacteriological examination should first consist in feeding a number of different species of animals the larger the number the better-for a day or two exclusively upon the food. White mice, house mice, white rats, young dogs,

The material under this heading was originally prepared by Dr. E. C. Noty, of Ann Arbor, Mich.

Fishchöder, Leitfaden der praktischen Fleischbeschau; Ostertag, Handbuch der Fleischbeschau; Walley, A Practical Guide to Meat Inspection.

cats, rabbits, or guinea pigs may be used. If the animals sicken and die, they are to be subsequently examined for the presence of pathogenic bacteria. It may happen that none of the animals thus fed will be injured by the food, which fact would not exclude, however, the presence of a germ requiring a specially susceptible animal for a subject.

Another set of animals should be injected with a cold extract of the meat made with sterile water. If the animals die, they are to be examined for pathogenic bacteria. A third set of animals should receive similar injections, though of larger portions, of this aqueous extract which has been previously filtered through sterile porcelain. If the animals die from such injections, the same as with unfiltered solutions, it is evident that a soluble bacterial chemical poison is present.

The identification of the toxin produced by the germ is wholly out of the question. The most that can be done satisfactorily is to obtain, as above, a germ-free solution of the poison. It is wholly unnecessary to devote any space in this connection to the detection of the basic bacterial products, the ptomaines, since these bodies are mere cleavage products produced by some and not by other bacteria. Moreover, they are usually but very feebly poisonous, and therefore are not considered to be as important as formerly.a

A bacteriological examination proper should be made of the original poisonous meat and of all the animals that died either from eating the meat or from the injections of the aqueous extracts. The organism present in the animal, if any, must be isolable directly from the meat. If it happens, as it sometimes has, that the dead animals contain no germs, it is proof that they were killed by a toxin elaborated by a germ in the meat previous to the injection. Cultures from the meat will then reveal the germ, and the effects of its pure cultures should correspond to those observed with the poisonous meat.

To prepare the cultures from the original food, the latter should be cut out with a sterile knife and material should be taken from the inside, thus avoiding all chances of contamination. Several sets of beef-tea tubes and agar plates should be made. One set should be set aside in a Novy anaerobic jar at room temperature; a second similar set should be placed at a temperature of 37° C. A third set should be grown in the presence of air at room temperature, and a like set at a temperature of 37° C.

The full details of bacteriological methods must obviously be omitted in this connection. Such work requires a special laboratory and special drill. Those who may be further interested are referred to the works of Abbott, Novy, and Sternberg.

3. Preparation of Sample for Chemical Examination.-Provisional.

In the case of fresh meat, separate the sample as completely as possible from the bones and pass it rapidly and repeatedly through a sausage mill until thorough mixture and complete maceration are obtained. The sample must be kept on ice to prevent decomposition, and all of the determinations should be begun as soon as practicable after the sample is prepared. In the case of canned meats, pass the entire contents of a can through a sausage mill as directed above. Remove sausage from the casings and mix by repeated grinding in a sausage mill. Dry that portion of the sample which is not needed for analysis, extract with gasoline which boils below 60° C., allow the gasoline to evaporate spontaneously, and expel the last traces by heating for a short time on the steam bath. Neither the meat nor the separated fat should be heated longer than

For detailed methods see Vaughan and Novy, "Cellular Toxins," 4th edition, 1902.

necessary, owing to the tendency of the latter to decompose. Reserve the fat for examination according to the methods given under "XIX. Edible Oils and Fats," page 129. Fat must be kept in a cool place and the examination finished before it becomes rancid.

4. Moisture.-Provisional.

Proceed as directed under "VI. General Methods," page 38.

5. Ash.-Provisional.

Proceed as directed under "VI. General Methods," page 38.

6. Ether Extract or Crude Fat.-Provisional.

Proceed as directed under " VI. General Methods," page 39.

7. Nitrogenous Substances.—Provisional.

(a) TOTAL NITROGEN.

Employ either the Kjeldahl or the Gunning method (as given under “I. Fertilizers," p. 5) using about 2 grams of the fresh sample. The digestion with sulphuric acid should be continued at least four hours.

(b) INSOLUBLE PROTEIDS.

Thoroughly exhaust 2 grams of the sample with cold water after extraction with ether, filter, and determine nitrogen in the insoluble residue as directed under "(a) Total nitrogen." Multiply the percentage of nitrogen so obtained by 6.25 for the percentage of meat fiber or insoluble proteids. (In case the connective tissue is determined, a corresponding correction must be made in the percentage of insoluble proteids.)

(c) CONNECTIVE TISSUE.

Extract 10 grams with cold water as directed above, then boil the exhausted residue repeatedly with about 100 cc of water until the total extract amounts to approximately 1 liter. Filter, concentrate by evaporation, and determine the nitrogen content. Multiply the nitrogen so obtained by 5.55 to obtain the percentage of nitrogenous substances of connective tissue.

(d) COAGULABLE PROTEIDS.

(For uncooked meat only.)

Almost neutralize the filtrate from the insoluble proteids, leaving it still faintly acid, boil until the globulins are coagulated, filter, wash, transfer the filter paper and contents to a Kjeldahl flask, and determine nitrogen as directed above under "(a) Total nitrogen." Multiply the percentage of nitrogen obtained by 6.25 to obtain the percentage of coagulable proteid.

(e) PROTEOSES, PEPTONES, AND GELATIN.

Heat the filtrate from albumen and globulins, add a slight excess of tannic acid and a few drops of a saturated solution of alum, allow to cool, filter, and wash with cold water. Heat the filtrate from the tannic-acid precipitate almost