1. Alum:—a. (Robine and Parisot.) About 1⁄4 lb. of the suspected bread (somewhat stale or dry) is reduced to crumbs, macerated for 2 or 3 hours in cold water, and then squeezed through a clean piece of white linen. The liquid is next evaporated to dryness at a steam-heat, the residuum redissolved in a little hot water, and the solution filtered. Liquor of ammonia or a solution of sal-ammoniac, and a solution of chloride of barium added to the filtered liquid, give a white precipitate when ALUM is present.

When nearly the whole of the alum has suffered decomposition in the loaf, as is frequently the case, the following process is required:—

b. (M. Kuhlman.) 4 or 5 oz. of bread are reduced to ash, which is powdered and treated with nitric acid, the mixture evaporated to dryness, and about 1 oz. of hot water added. A little caustic potassa is added to the last solution (unfiltered), the whole boiled a few minutes, and passed through a filter. The filtrate is next tested with a solution of sal-ammoniac, and the whole again boiled for 2 or 3 minutes. If a precipitate forms it is alumina; every 50 gr. of which are equivalent to 332 gr. of crystallised alum.

c. The suspected sample is wetted with a weak solution of logwood, or, preferably, of cochineal. Pure bread is only slightly stained by this solution; bread containing alum strikes a lavender, lilac, or purple colour, according to the quantity of the adulterant present. If it acquires a pearl-grey or bluish tint, some alkali (potash, soda, or ammonia) is present.

d. (J. A. Wanklyn.) 100 grams of bread are incinerated in a platinum dish, capable of holding the whole quantity at once. The incineration is managed at a comparatively low temperature, and takes some four or five hours; the platinum dish being heated by means of a large Bunsen burner, abundantly supplied with air. It is well to continue the ignition until the bread-ash is nearly completely burnt, and it is advisable to weigh the dish containing the ash. The weight of the ash should not sensibly exceed 2 grams. The ash having been obtained is then moistened with 3 c. c. of pure strong hydrochloric acid, and then some 20 to 30 c. c. of distilled water is added, and the whole is boiled, filtered, and the precipitate washed several times with boiling water. In this manner a precipitate consisting of a silica, together with some unburnt carbon, is left on the filter, whilst the filtrate contains the phosphates. The precipitate, which, after being burnt, consists of silica, is weighed. The filtrate is mixed with 5 c. c. of ammonia (sp. gr. 0·880), whereby it is rendered powerfully alkaline and opaque, owing to the precipitation of the phosphates. It is finally mixed gradually with some 20 c. c. of strong acetic acid, and as the acid is being poured in, it is to be observed that the liquid is alkaline and opaque, until some 5 c. c. of the acid have been added; that when about 10 c. c. have been added the liquid is acid and much clearer, and that at least 10 c. c. of strong acetic acid are added after the establishment of a distinctly acid reaction. The liquid is then boiled and filtered, and the precipitates, consisting of phosphates of alumina and iron, well-washed with boiling water, ignited and weighed. The last step is the determination of the iron in the weighed precipitate, and this is accomplished either by reduction and titration with standard solution of permanganate in the well known manner, or else by a colour process, viz., by trituration with ferrocyanide of potassium. Having ascertained the amount of iron in the precipitate of mixed phosphates, it is only necessary to calculate it into phosphate of iron, and to subtract the weight of phosphate of iron from the total weight of the mixed phosphates, and the difference is the phosphate of alum yielded by 100 grams of the bread. The following results have been obtained by applying the above-described process to samples of bread presumed to be free from alum:—

From 100 grams of Bread.


Bread-ash.
Silica.		Precipitate
insoluble in
acetic acid.
Grams.Grams.Grams.
A1·408...0·010
B1·378...0·006
C1·7300·0180·010
D1·6200·0320·014
E......0·012
(1)F1·3830·0300·012
(2)F1·3240·0250·014

The precipitate insoluble in acetic acid contained in every instance a large proportion of iron, but in some cases at least did not wholly consist of phosphate of iron. On deducting the quantity of phosphate of iron from the total phosphates insoluble in acetic acid, there remains a residue of some five or six milligrams. It would therefore appear that unalumed

bread is liable to contain a minute trace of alumina, which, expressed as phosphate of alumina (Al2O3PO5), equals five or six milligrams per 100 grains of bread, or 0·005 per cent. If the alum corresponding to this phosphate be calculated, it will be seen that 100 grams of unalumed bread may appear to contain 0·022 grams of alum; or expressed on the 4-lb. loaf, there may appear to be 6 grams of alum in it. This agrees very fairly with Dr Dupré’s observation.

e. (J. C. Thresh.) The author states that this process requires only a few hours, and quotes experiments, showing the accuracy of the results:—