and insoluble in water; if dilute hydrochloric acid dissolves entirely these particles with the evolution of carbonic acid, carbonate of lime or carbonate of magnesia are present. To distinguish between them, burn a sample of the flour to a white ash on a foil of platinum, dissolve the residue in dilute hydrochloric acid, and filter; finally, add to the filtered fluid ammonia and phosphate of soda; the occurrence of a crystalline precipitate will be a proof that the amorphous particles seen with the microscope, consist partly if not entirely of carbonate of magnesia. If no crystalline precipitate be formed, to another sample of the original solution add ammonia and oxalic acid, the appearance of a precipitate insoluble in acetic acid will show the presence of lime. If the co-existence of lime and magnesia or their carbonate be suspected in flour, the ashes of the incinerated meal, being dissolved in weak hydrochloric acid, are tested first with ammonia and carbonate of ammonia, which throws down all the lime in the form of carbonate of lime; the fluid filtered from this precipitate is now mixed with phosphate of soda and more ammonia, when the magnesia will be precipitated in the crystalline combination known as the phosphate of ammonia and magnesia. To determine the amount of lime and magnesia contained in the ashes of a weighed quantity of adulterated flour, the analyst must proceed as directed for the qualitative analysis just described; the lime and magnesia precipitates are to be collected on separate filters, and subsequently burnt and weighed. This method does not yield chemically exact results, they can only be considered as approximations, but will suffice for all practical purposes. 1100 parts of the burnt magnesia, precipitate › Phosphoric acid, 63.36. or pyrophosphate of magnesia, contain. Magnesia, 36.64 100.00 Bone dust, or phosphate of lime.-For the detection of this adulteration a knowledge of the structure of bonetissue and a microscope may suffice; in case the reader should not be acquainted with microscopical physiology, he may again call in aid chemical analysis, and by a very short and easy process detect the adulteration; this is done by burning the suspected flour to a white ash, a portion of which is subsequently treated with water, and filtered; if the substance on the filter dissolves by the addition of dilute hydrochloric acid, without the evolution of carbonic acid; and if in this solution, neutralised with ammonia, oxalic acid produces a granular precipitate, insoluble in acetic acid, and molybdate of ammonia with nitric acid, a yellow precipitate when the mixture is heated, the foreign substance is proved to consist of phosphate of lime. Another short method is alluded to in the synoptical table of the adulterations of flour. (See page 22.) Sulphate of lime.-When sulphate of lime (gypsum, or plaster of Paris) has been added to flour, the operator is first led to suspect the fraud by the appearance under the microscope of small amorphous particles having no organized structure, and mixed with the starch corpuscles; if the addition of hydrochloric acid does not decompose them, with evolution of carbonic acid, these molecules consist of sulphate of lime, or silica (sand). A sample of the flour is now burnt on a charcoal support, mixed with a little carbonate of soda and borax, and fused. The fused mass being placed upon a clean silver surface, say a bright shilling, and a drop of water being added, if sulphate of lime is present a black stain will be produced on the shilling, with the evolution of sulphuretted hydrogen. On washing the silver, the spot becomes evident. Silica (sand) may exist in flour from its being added with the view of adulterating the meal, or perhaps being detached accidentally from the millstone. Its presence can be detected, along with that of clay, by the occurrence of small particles in the field of the microscope mixed with the starch corpuscles, and which, by the application of the above-mentioned tests, are not found to consist of bone dust, carbonate or sulphate of lime, and carbonate of magnesia. A better means, however, for discovering the existence of silica in flour is to fuse a sample of the ashes of the farina with a small quantity of microcosmic salt (phosphate of soda and ammonia), and then expose the mixture to the blowpipe flame on a platina wire, a bead will thus be formed, remaining perfectly transparent if no silica be present, and exhibiting opaque specks if it should exist therein, even in the smallest quantity. (Plattner, On the Use of the Blowpipe,' p. 239.) . Clay, or Silicate of alumina.-The presence of this adulteration may be detected by treating the ashes of the flour with water; an insoluble residue will thus be obtained, which, when placed on the charcoal support, moistened with nitrate of cobalt, and exposed to the blowpipe flame, assumes a beautiful sky-blue colour. As a further proof, let the insoluble residue be tested with microcosmic salt in the blowpipe flame, for the detection of silica. Alum (sulphate of alumina and potash, or sulphate of alumina and ammonia) is very often employed for the adulteration of flour, with the view of increasing the white appearance of the bread, and its power of retaining water. As alum is soluble in water, its presence is to be looked for in an aqueous extract of flour. If a sample of the meal be mixed with water, the fluid expressed through a cloth, and allowed to stand for some hours, a comparatively clear liquor is obtained. A small quantity of the fluid being decanted, if a precipitate is induced therein by ammonia and chloride of ammonium, with the application of heat, alum is very probably present; for a confirmatory test, the precipitate may be collected on a filter, dried, and burnt on a charcoal support with the blowpipe flame; a few drops of a solution of nitrate of cobalt are added to the substance, which, being again heated with the blowpipe, exhibits a blue colour if alumina be present. For sake of practical convenience, I have condensed the methods of analysis, for the detection of the adulterations of flour, into the following synoptical table— SYNOPTICAL TABLE, showing how to analyse Flour with the view of detecting its Adulterations. Gluten. Nature determined by drawing into threads. Alum (adulteration), precipitated by the addition of ammonia and chloride of ammonium, with the applica- Sugar. Gives an orange-coloured precipitate with sulphate of copper and potash. Carbonate of [tion of heat. Microscopical examination-Small amorphous specks. ammonia. Microscopical examination-Small amorphous specks. Bone-dust Microscopical examination-Small amorphous particles. Microscopical examination-Large amorphous particles, of Chemical examination-Insoluble in hydrochloric acid; an opaque bead when ashes of flour are fused in blowpipe flame with microcosmic salt. Microscopical examination-Amorphous particles. Chemical examination-A blue colour produced when ashes are treated with nitrate of cobalt and fused with blowpipe. |