Pour upon two ounces of the suspected bread, half a pint of boiling distilled water; boil the mixture for a few minutes, and filter it through unsized paper. Evaporate the fluid, to about one fourth of its original bulk, and let gradually fall into the clear fluid a solution of muriate of barytes. If a [Pg 109]copious white precipitate ensues, which does not disappear by the addition of pure nitric acid, the presence of alum may be suspected. Bread, made without alum, produces, when assayed in this manner, merely a very slight precipitate, which originates from a minute portion of sulphate of magnesia contained in all common salt of commerce; and bread made with salt freed from sulphate of magnesia, produces an infusion with water, which does not become disturbed by the barytic test.
Other means of detecting all the constituent parts of alum, namely, the alumine, sulphuric acid, and potash, so as to render the presence of the alum unequivocal, will readily suggest itself to those who are familiar with analytical chemistry; namely: one of the readiest means is, to decompose the vegetable matter of the bread, by the action of chlorate of potash, in a platina crucible, at a red heat, and then to assay the residuary mass—by means of muriate of barytes, for sulphuric acid; by ammonia, for alumine; and by muriate of platina, for potash[46]. The above method of detecting [Pg 110]the presence of alum, must therefore be taken with some limitation.
There is no unequivocal test for detecting in a ready manner the presence of alum in bread, on account of the impurity of the common salt used in the making of bread. If we could, in the ordinary way of bread making, employ common salt, absolutely free from foreign saline substances, the mode of detecting the presence of alum, or at least one of its constituent parts, namely, the sulphuric acid, would be very easy. Some conjecture may, nevertheless, be formed of the presence, or absence, of alum, by assaying the infusion of bread in the manner stated, p. 109, and comparing the assay with the results afforded by an infusion of home-made or household bread, known to be genuine, and actually assayed in a similar manner.
Other means of detecting all the constituent parts of alum, namely, the alumine, sulphuric acid, and potash, so as to render the presence of the alum unequivocal, will readily suggest itself to those who are familiar with analytical chemistry; namely: one of the readiest means is, to decompose the vegetable matter of the bread, by the action of chlorate of potash, in a platina crucible, at a red heat, and then to assay the residuary mass—by means of muriate of barytes, for sulphuric acid; by ammonia, for alumine; and by muriate of platina, for potash[46]. The above method of detecting [Pg 110]the presence of alum, must therefore be taken with some limitation.
There is no unequivocal test for detecting in a ready manner the presence of alum in bread, on account of the impurity of the common salt used in the making of bread. If we could, in the ordinary way of bread making, employ common salt, absolutely free from foreign saline substances, the mode of detecting the presence of alum, or at least one of its constituent parts, namely, the sulphuric acid, would be very easy. Some conjecture may, nevertheless, be formed of the presence, or absence, of alum, by assaying the infusion of bread in the manner stated, p. 109, and comparing the assay with the results afforded by an infusion of home-made or household bread, known to be genuine, and actually assayed in a similar manner.
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