CANNED MEAT
If in preparing canned meat only fresh meat is used, there is little need for the use of preservatives, but as considerable smoked and cured meat is thus used, preservatives may find their way into canned meat.
The same preservatives should be looked for as in fresh and smoked meat and the same test made for each.
Heavy Metals
A. H. Allen’s Method.—About 25 grams of the substance is mixed slowly with enough strong, pure sulfuric acid to just moisten the mass, avoiding an excess. Heat on a water-bath for a short time, then raise the temperature gradually, and maintain till the chlorids seem to be decomposed. It must not be hot enough, however, to volatilize the sulfuric acid. Then add 1 cc. of strong nitric acid and heat till red fumes are given off. Freshly ignited magnesia in the proportion of 0.5 gram for each cc. of sulfuric and nitric acid previously used is now stirred into the mass and the whole ignited at a dull red heat. This is best done in a gas-muffle. When cool, moisten the ash with nitric acid and gently re-ignite, repeating this treatment till the carbon is entirely consumed. Treat the residue with 8 or 10 drops of strong sulfuric acid, heat till fumes are given off, cool, boil with water, dilute to about 100 cc. and saturate with hydrogen sulfid, filter, examine as follows:
| Zinc and iron may be in solution. Add bromine water to destroy hydrogen sulfid and to oxidizethe iron, boil and add ammonium hydrate in excess, boil again and filter. | Lead, tin, copper, and calcium, if present, will be in the precipitate and residue. Fuse the massin a porcelain crucible for at least ten minutes with 2 grams each of potassium and sodium carbonates and half as much sulfur. Aftercooling, boil with water and filter. | ||
| The precipitate will contain the iron and the phosphates. | Filtrate, when blue, proves the presence of nickel. | Residue. Add hydrochloric acid and boil as long as hydrogen sulfid is given off. A few drops ofbromine water will complete the oxidation of the copper sulfid. Filter, and add ammonium hydroxid in excess to the filtrate. When thefiltrate is blue, it indicates the presence of copper. Acidify the filtrate with acetic acid and test for lead by adding potassiumchromate, a yellow precipitate being formed when it is present. | The filtrate may contain tin. Acidify with acetic acid, and if tin is present a yellow precipitateof stannic sulfid will form. |
| I. Heat to boiling and add potassium ferrocyanid. A white precipitate or turbidity indicateszinc. | |||